On Oct 14, 4:59=A0pm, dagmargoodb...@yahoo.com wrote:> On Oct 14, 2:41=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > > > > On Oct 13, 10:13=A0pm, dagmargoodb...@yahoo.com wrote: > > > On Oct 13, 6:30=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > On Oct 13, 5:13=A0pm, Phil Hobbs wrote: > > > > > On 10/13/2011 12:39 PM, George Herold wrote: > > > > > > > This is a continuation of the 50kHz VCO thread I started last w=eek. =A0I> > > > > > tried the stepped sine wave idea as suggested by James A, and P=hil> > > > > > H. > > > > > > The circuit clocks a MC14017 at 10x(F) to make a stepped sine w=ave at> > > > > > frequency (F). =A0The ten outputs from the 4017 are sent throug=h> > > > > > appropriate resistors and into the summing junction of an opamp=.> > > > > > Here=92s a =91scope shot of the stepped output overlaid with a =sine> > > > > > wave. > > > > > > >http://imageshack.us/photo/my-images/560/tek0024.png/ > > > > > > > The resistor values were chosen to intersect the sine wave at e=ach new> > > > > > phase. =A0(R(n) =3D 1/sin^2(n*18degrees)) > > > > > > > Approximate values, R0=3Dopen, R1=3DR9=3D105k, R2=3DR8=3D28.9k,=R3=3DR7=3D15.3k,> > > > > > R4=3DR6=3D11k, R5=3D10k. =A0all 1% resistors. > > > > > > > Here=92s the spectrum as recorded by an SRS770 spectrum analyze=r.> > > > > > >http://imageshack.us/photo/my-images/839/stepsin.png/ > > > > > > > The 2nd harmonic is only down by 50dB. =A0I don=92t understand =why it=92s so> > > > > > big. =A0Is there some way to do better than this? =A0The 9th an=d 11th> > > > > > harmonics are big and then the 19th and 21st. > > > > > > 50 dB is only 0.3%, which isn't too bad. =A0 That might easily be=due to> > > > > the output impedances of the 4017 drivers, or to the resistor > > > > > tolerances. =A0Does it get better or worse when you change VDD? ==A0If so,> > > > > it's probably the output impedance. > > > > > Yeah, I was thinking about the output impedance. (I didn't looked a=t> > > > the outputs from the 4017). =A0When I decreased the supply voltage =the> > > > 2nd harmonic was roughly constant while everything else went down. ==A0I> > > > added a tweaker on the lowest resistance output and got everything > > > > below the 9th close to 60 dB down. =A0 Which is almost beer time, e=xcept> > > > it's only at 1kHz. > > > > I posted (and Google lost) a long post, the gist of which was: > > > > (view in fixed font) > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0desired, > > > G.H. =A0 =A0desired, =A0 scaled to =A0George's > > > values theoretical 'scope =A0 =A0 actual > > > (volts) (volts) =A0 =A0(div) =A0 =A0 =A0(div) > > > 0.000 =A0 0.000 =A0 =A0 =A0 0.2 =A0 =A0 =A0 =A00.2 > > > 0.093 =A0 0.079 =A0 =A0 =A0 0.93 =A0 =A0 =A0 1.0 > > > 0.323 =A0 0.287 =A0 =A0 =A0 2.82 =A0 =A0 =A0 2.8 > > > 0.577 =A0 0.545 =A0 =A0 =A0 5.17 =A0 =A0 =A0 5.2 > > > 0.768 =A0 0.753 =A0 =A0 =A0 7.07 =A0 =A0 =A0 7.05 > > > 0.832 =A0 0.832 =A0 =A0 =A0 7.8 =A0 =A0 =A0 =A07.8 > > > > (1rst column is the expected outputs based on your resistor values) > > > > So, the outputs are loaded, but you've tweaked the resistors from the > > > reported values to compensate. =A0That's device-dependent. =A0Might w=anna> > > up the resistances or switch to 'HC. > > > > The actual waveform looks pretty good. =A0Some of the steps look a > > > little mis-matched, e.g. 2-8 and 3-7 > > > Hi James, =A0Yeah I was loading down the output of the 4017. =A0I measu=red> > an output impedance of ~180 ohms. =A0I put this number in and > > recalcualted values, =A0and then selected them to ~0.1% with a DMM. =A0=The> > result.... I've got all the harmonics below the 9th down by ~70dB! =A0I > > don't know how repeatable the the output imedance is? =A0I put in a few > > different 4017's and say no difference, but these were all from the > > same order, so... > > > Here's a plot from the SRS770.http://imageshack.us/photo/my-images/7/vc=o2.png/> > Beautiful, and well worth the resistors, right? =A0Compared to the cost > and complexity of extra hardware, it's a bargain.Yeah, I was hoping for 60dB. When I crank up the frequency capacitance is going to start to byte me, but now I've got dB's to spare.> > For each half-wave, I'd analyze this as the sum of three impulses, one > inside the other, added together. =A0The phasing and amplitude of those > impulses is critical to canceling harmonics. > > =A0 =A0 =A0 =A0 .---. > =A0 =A0 =A0.--' =A0 '--. > =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > =A0 =A0.-' =A0 =A0 =A0 =A0 '-. > ___| =A0 =A0 =A0 =A0 =A0 =A0 |___ > =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 | > =A0 -' =A0 =A0 =A0 =A0 =A0 =A0 '- > > My gut wants to say--but I'm too lazy to prove right now--that having > the same voltages repeated symmetrically on either side of each peak > is critical to harmonic rejection.Hmm you're suggesting that matching between equal value resistors is more important than hitting some exact number. I think, that might be true.... or does matching effect the odd harmonics and absolute value the even? George H.> > Where the voltage is unequal on either side, you introduce a new > impulse with a magnitude equal to the difference in voltages. It's > easy to *introduce* a 2nd harmonic component that way. =A0For example, > taking the middle impulse: > > =A0 =A0.-----. > =A0 =A0| =A0 =A0 '----. > =A0 =A0| =A0 =A0 =A0 =A0 =A0| > =A0 =A0| =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > ___|__________|_________|__ > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > =A0 =A0 =A0 =A0 =A0 =A0 =A0 |____ =A0 =A0 | > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'----' > > My original thinking was to have an up/down counter, a single homemade > DAC, cycle up and down through the same (sine-weighted) values, then > invert (externally) for the negative swing. =A0That gets you 4x as many > steps and automatic symmetry, but it's not nearly as cute as Phil's > 4017. > > > Now I've got to get it off the white proto-board and crank up the > > frequency. > > > George H. > > -- > Cheers, > James Arthur- Hide quoted text - > > - Show quoted text -
Stepped sine wave
Started by ●October 13, 2011
Reply by ●October 15, 20112011-10-15
Reply by ●October 15, 20112011-10-15
On Oct 14, 8:07=A0pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> On 10/14/2011 03:41 PM, George Herold wrote: > > > > > > > On Oct 13, 10:13 pm, dagmargoodb...@yahoo.com wrote: > >> On Oct 13, 6:30 pm, George Herold<gher...@teachspin.com> =A0wrote: > > >>> On Oct 13, 5:13 pm, Phil Hobbs wrote: > >>>> On 10/13/2011 12:39 PM, George Herold wrote: > > >>>>> This is a continuation of the 50kHz VCO thread I started last week.==A0I> >>>>> tried the stepped sine wave idea as suggested by James A, and Phil > >>>>> H. > >>>>> The circuit clocks a MC14017 at 10x(F) to make a stepped sine wave =at> >>>>> frequency (F). =A0The ten outputs from the 4017 are sent through > >>>>> appropriate resistors and into the summing junction of an opamp. > >>>>> Here s a scope shot of the stepped output overlaid with a sine > >>>>> wave. > > >>>>>http://imageshack.us/photo/my-images/560/tek0024.png/ > > >>>>> The resistor values were chosen to intersect the sine wave at each =new> >>>>> phase. =A0(R(n) =3D 1/sin^2(n*18degrees)) > > >>>>> Approximate values, R0=3Dopen, R1=3DR9=3D105k, R2=3DR8=3D28.9k, R3==3DR7=3D15.3k,> >>>>> R4=3DR6=3D11k, R5=3D10k. =A0all 1% resistors. > > >>>>> Here s the spectrum as recorded by an SRS770 spectrum analyzer. > > >>>>>http://imageshack.us/photo/my-images/839/stepsin.png/ > > >>>>> The 2nd harmonic is only down by 50dB. =A0I don t understand why it=s so> >>>>> big. =A0Is there some way to do better than this? =A0The 9th and 11=th> >>>>> harmonics are big and then the 19th and 21st. > > >>>> 50 dB is only 0.3%, which isn't too bad. =A0 That might easily be du=e to> >>>> the output impedances of the 4017 drivers, or to the resistor > >>>> tolerances. =A0Does it get better or worse when you change VDD? =A0I=f so,> >>>> it's probably the output impedance. > > >>> Yeah, I was thinking about the output impedance. (I didn't looked at > >>> the outputs from the 4017). =A0When I decreased the supply voltage th=e> >>> 2nd harmonic was roughly constant while everything else went down. ==A0I> >>> added a tweaker on the lowest resistance output and got everything > >>> below the 9th close to 60 dB down. =A0 Which is almost beer time, exc=ept> >>> it's only at 1kHz. > > >> I posted (and Google lost) a long post, the gist of which was: > > >> (view in fixed font) > >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 desired, > >> G.H. =A0 =A0desired, =A0 scaled to =A0George's > >> values theoretical 'scope =A0 =A0 actual > >> (volts) (volts) =A0 =A0(div) =A0 =A0 =A0(div) > >> 0.000 =A0 0.000 =A0 =A0 =A0 0.2 =A0 =A0 =A0 =A00.2 > >> 0.093 =A0 0.079 =A0 =A0 =A0 0.93 =A0 =A0 =A0 1.0 > >> 0.323 =A0 0.287 =A0 =A0 =A0 2.82 =A0 =A0 =A0 2.8 > >> 0.577 =A0 0.545 =A0 =A0 =A0 5.17 =A0 =A0 =A0 5.2 > >> 0.768 =A0 0.753 =A0 =A0 =A0 7.07 =A0 =A0 =A0 7.05 > >> 0.832 =A0 0.832 =A0 =A0 =A0 7.8 =A0 =A0 =A0 =A07.8 > > >> (1rst column is the expected outputs based on your resistor values) > > >> So, the outputs are loaded, but you've tweaked the resistors from the > >> reported values to compensate. =A0That's device-dependent. =A0Might wa=nna> >> up the resistances or switch to 'HC. > > >> The actual waveform looks pretty good. =A0Some of the steps look a > >> little mis-matched, e.g. 2-8 and 3-7 > > >> -- > >> Cheers, > >> James Arthur- Hide quoted text - > > >> - Show quoted text - > > > Hi James, =A0Yeah I was loading down the output of the 4017. =A0I measu=red> > an output impedance of ~180 ohms. =A0I put this number in and > > recalcualted values, =A0and then selected them to ~0.1% with a DMM. =A0=The> > result.... I've got all the harmonics below the 9th down by ~70dB! =A0I > > don't know how repeatable the the output imedance is? =A0I put in a few > > different 4017's and say no difference, but these were all from the > > same order, so... > > > Here's a plot from the SRS770. > >http://imageshack.us/photo/my-images/7/vco2.png/ > > > Now I've got to get it off the white proto-board and crank up the > > frequency. > > > George H. > > Cool! =A0 4017s rule--they're dead useful and just complicated enough tha=t> the anti-555 fascists don't notice. :) > > I use them for things like getting guaranteed break-before-make from > 74HC4016-style analogue switches. =A0Of course, I've also used PALs as > analogue components, so I have no shame whatever. > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal Consultant > ElectroOptical Innovations LLC > Optics, Electro-optics, Photonics, Analog Electronics > > 160 North State Road #203 > Briarcliff Manor NY 10510 > 845-480-2058 > > hobbs at electrooptical dot nethttp://electrooptical.net- Hide quoted tex=t -> > - Show quoted text -Oh, Thank you Phil! I'm not above anything that gets the job done. George H.
Reply by ●October 15, 20112011-10-15
On Oct 14, 4:59=A0pm, dagmargoodb...@yahoo.com wrote:> On Oct 14, 2:41=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > > > > On Oct 13, 10:13=A0pm, dagmargoodb...@yahoo.com wrote: > > > On Oct 13, 6:30=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > On Oct 13, 5:13=A0pm, Phil Hobbs wrote: > > > > > On 10/13/2011 12:39 PM, George Herold wrote: > > > > > > > This is a continuation of the 50kHz VCO thread I started last w=eek. =A0I> > > > > > tried the stepped sine wave idea as suggested by James A, and P=hil> > > > > > H. > > > > > > The circuit clocks a MC14017 at 10x(F) to make a stepped sine w=ave at> > > > > > frequency (F). =A0The ten outputs from the 4017 are sent throug=h> > > > > > appropriate resistors and into the summing junction of an opamp=.> > > > > > Here=92s a =91scope shot of the stepped output overlaid with a =sine> > > > > > wave. > > > > > > >http://imageshack.us/photo/my-images/560/tek0024.png/ > > > > > > > The resistor values were chosen to intersect the sine wave at e=ach new> > > > > > phase. =A0(R(n) =3D 1/sin^2(n*18degrees)) > > > > > > > Approximate values, R0=3Dopen, R1=3DR9=3D105k, R2=3DR8=3D28.9k,=R3=3DR7=3D15.3k,> > > > > > R4=3DR6=3D11k, R5=3D10k. =A0all 1% resistors. > > > > > > > Here=92s the spectrum as recorded by an SRS770 spectrum analyze=r.> > > > > > >http://imageshack.us/photo/my-images/839/stepsin.png/ > > > > > > > The 2nd harmonic is only down by 50dB. =A0I don=92t understand =why it=92s so> > > > > > big. =A0Is there some way to do better than this? =A0The 9th an=d 11th> > > > > > harmonics are big and then the 19th and 21st. > > > > > > 50 dB is only 0.3%, which isn't too bad. =A0 That might easily be=due to> > > > > the output impedances of the 4017 drivers, or to the resistor > > > > > tolerances. =A0Does it get better or worse when you change VDD? ==A0If so,> > > > > it's probably the output impedance. > > > > > Yeah, I was thinking about the output impedance. (I didn't looked a=t> > > > the outputs from the 4017). =A0When I decreased the supply voltage =the> > > > 2nd harmonic was roughly constant while everything else went down. ==A0I> > > > added a tweaker on the lowest resistance output and got everything > > > > below the 9th close to 60 dB down. =A0 Which is almost beer time, e=xcept> > > > it's only at 1kHz. > > > > I posted (and Google lost) a long post, the gist of which was: > > > > (view in fixed font) > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0desired, > > > G.H. =A0 =A0desired, =A0 scaled to =A0George's > > > values theoretical 'scope =A0 =A0 actual > > > (volts) (volts) =A0 =A0(div) =A0 =A0 =A0(div) > > > 0.000 =A0 0.000 =A0 =A0 =A0 0.2 =A0 =A0 =A0 =A00.2 > > > 0.093 =A0 0.079 =A0 =A0 =A0 0.93 =A0 =A0 =A0 1.0 > > > 0.323 =A0 0.287 =A0 =A0 =A0 2.82 =A0 =A0 =A0 2.8 > > > 0.577 =A0 0.545 =A0 =A0 =A0 5.17 =A0 =A0 =A0 5.2 > > > 0.768 =A0 0.753 =A0 =A0 =A0 7.07 =A0 =A0 =A0 7.05 > > > 0.832 =A0 0.832 =A0 =A0 =A0 7.8 =A0 =A0 =A0 =A07.8 > > > > (1rst column is the expected outputs based on your resistor values) > > > > So, the outputs are loaded, but you've tweaked the resistors from the > > > reported values to compensate. =A0That's device-dependent. =A0Might w=anna> > > up the resistances or switch to 'HC. > > > > The actual waveform looks pretty good. =A0Some of the steps look a > > > little mis-matched, e.g. 2-8 and 3-7 > > > Hi James, =A0Yeah I was loading down the output of the 4017. =A0I measu=red> > an output impedance of ~180 ohms. =A0I put this number in and > > recalcualted values, =A0and then selected them to ~0.1% with a DMM. =A0=The> > result.... I've got all the harmonics below the 9th down by ~70dB! =A0I > > don't know how repeatable the the output imedance is? =A0I put in a few > > different 4017's and say no difference, but these were all from the > > same order, so... > > > Here's a plot from the SRS770.http://imageshack.us/photo/my-images/7/vc=o2.png/> > Beautiful, and well worth the resistors, right? =A0Compared to the cost > and complexity of extra hardware, it's a bargain. > > For each half-wave, I'd analyze this as the sum of three impulses, one > inside the other, added together. =A0The phasing and amplitude of those > impulses is critical to canceling harmonics. > > =A0 =A0 =A0 =A0 .---. > =A0 =A0 =A0.--' =A0 '--. > =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > =A0 =A0.-' =A0 =A0 =A0 =A0 '-. > ___| =A0 =A0 =A0 =A0 =A0 =A0 |___ > =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 | > =A0 -' =A0 =A0 =A0 =A0 =A0 =A0 '- > > My gut wants to say--but I'm too lazy to prove right now--that having > the same voltages repeated symmetrically on either side of each peak > is critical to harmonic rejection.Hmm you're suggesting that matching between equal value resistors it more important than hitting exact values?> > Where the voltage is unequal on either side, you introduce a new > impulse with a magnitude equal to the difference in voltages. It's > easy to *introduce* a 2nd harmonic component that way. =A0For example, > taking the middle impulse: > > =A0 =A0.-----. > =A0 =A0| =A0 =A0 '----. > =A0 =A0| =A0 =A0 =A0 =A0 =A0| > =A0 =A0| =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > ___|__________|_________|__ > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > =A0 =A0 =A0 =A0 =A0 =A0 =A0 |____ =A0 =A0 | > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'----' > > My original thinking was to have an up/down counter, a single homemade > DAC, cycle up and down through the same (sine-weighted) values, then > invert (externally) for the negative swing. =A0That gets you 4x as many > steps and automatic symmetry, but it's not nearly as cute as Phil's > 4017. > > > Now I've got to get it off the white proto-board and crank up the > > frequency. > > > George H. > > -- > Cheers, > James Arthur- Hide quoted text - > > - Show quoted text -
Reply by ●October 15, 20112011-10-15
On Oct 14, 11:25=A0pm, George Herold <gher...@teachspin.com> wrote:> On Oct 14, 4:59=A0pm, dagmargoodb...@yahoo.com wrote: > > On Oct 14, 2:41=A0pm, George Herold <gher...@teachspin.com> wrote:> > > Hi James, =A0Yeah I was loading down the output of the 4017. =A0I mea=sured> > > an output impedance of ~180 ohms. =A0I put this number in and > > > recalcualted values, =A0and then selected them to ~0.1% with a DMM. ==A0The> > > result.... I've got all the harmonics below the 9th down by ~70dB! ==A0I> > > don't know how repeatable the the output imedance is? =A0I put in a f=ew> > > different 4017's and say no difference, but these were all from the > > > same order, so... > > > > Here's a plot from the SRS770.http://imageshack.us/photo/my-images/7/=vco2.png/> > > Beautiful, and well worth the resistors, right? =A0Compared to the cost > > and complexity of extra hardware, it's a bargain. > > > For each half-wave, I'd analyze this as the sum of three impulses, one > > inside the other, added together. =A0The phasing and amplitude of those > > impulses is critical to canceling harmonics. > > > =A0 =A0 =A0 =A0 .---. > > =A0 =A0 =A0.--' =A0 '--. > > =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > > =A0 =A0.-' =A0 =A0 =A0 =A0 '-. > > ___| =A0 =A0 =A0 =A0 =A0 =A0 |___ > > =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 | > > =A0 -' =A0 =A0 =A0 =A0 =A0 =A0 '- > > > My gut wants to say--but I'm too lazy to prove right now--that having > > the same voltages repeated symmetrically on either side of each peak > > is critical to harmonic rejection. > > Hmm you're suggesting that matching between equal value resistors it > more important than hitting exact values?I'm suggesting the possibility, but that's only a suspicion--I showed one example below. OTOH, I also just installed a virtual caterpillar grommet backwards in another thread. :-) As a practical matter, Phil's 'HC4017 with precision resistors seems best.> > Where the voltage is unequal on either side, you introduce a new > > impulse with a magnitude equal to the difference in voltages. It's > > easy to *introduce* a 2nd harmonic component that way. =A0For example, > > taking the middle impulse: > > > =A0 =A0.-----. > > =A0 =A0| =A0 =A0 '----. > > =A0 =A0| =A0 =A0 =A0 =A0 =A0| > > =A0 =A0| =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > > ___|__________|_________|__ > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 |____ =A0 =A0 | > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'----' > > > My original thinking was to have an up/down counter, a single homemade > > DAC, cycle up and down through the same (sine-weighted) values, then > > invert (externally) for the negative swing. =A0That gets you 4x as many > > steps and automatic symmetry, but it's not nearly as cute as Phil's > > 4017.FWIW, here's what I'd imagined, where v0-v7 encode a half-wave: 'HC4051 .-----. v7-----|0 | v6-----|1 | v5-----|2 | v4-----|3 Y|---- v3-----|4 | v2-----|5 | v1-----|6 | v0-----|7 | | ABC | '-----' ||| .---. |XOR|<-. '---' | ||| .-' ||| | .------. | ABC D| 16x clk -|> | 4-bit Counter | | '------' This logic walks up and down through 8 voltages, which, since they are reused from the same source, are duplicated exactly on each side of the peak. That does not guarantee symmetry about zero, though. Another possibility is to make v0-v7 encode a quarter-wave, then multiply by +/-1 afterwards in analog, ensuring full symmetry. Mine's three chips, minimum, to Phil's one. My original goal was to ease filtering by maximizing steps. I'm not ultimately sure this is any better w.r.t. even harmonics--that could be resistor-precision limited...I haven't done the math. -- Cheers, James Arthur
Reply by ●October 15, 20112011-10-15
On Oct 15, 9:31=A0am, dagmargoodb...@yahoo.com wrote:> On Oct 14, 11:25=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > > > > On Oct 14, 4:59=A0pm, dagmargoodb...@yahoo.com wrote: > > > On Oct 14, 2:41=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > Hi James, =A0Yeah I was loading down the output of the 4017. =A0I m=easured> > > > an output impedance of ~180 ohms. =A0I put this number in and > > > > recalcualted values, =A0and then selected them to ~0.1% with a DMM.==A0The> > > > result.... I've got all the harmonics below the 9th down by ~70dB! ==A0I> > > > don't know how repeatable the the output imedance is? =A0I put in a=few> > > > different 4017's and say no difference, but these were all from the > > > > same order, so... > > > > > Here's a plot from the SRS770.http://imageshack.us/photo/my-images/=7/vco2.png/> > > > Beautiful, and well worth the resistors, right? =A0Compared to the co=st> > > and complexity of extra hardware, it's a bargain. > > > > For each half-wave, I'd analyze this as the sum of three impulses, on=e> > > inside the other, added together. =A0The phasing and amplitude of tho=se> > > impulses is critical to canceling harmonics. > > > > =A0 =A0 =A0 =A0 .---. > > > =A0 =A0 =A0.--' =A0 '--. > > > =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > > > =A0 =A0.-' =A0 =A0 =A0 =A0 '-. > > > ___| =A0 =A0 =A0 =A0 =A0 =A0 |___ > > > =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 | > > > =A0 -' =A0 =A0 =A0 =A0 =A0 =A0 '- > > > > My gut wants to say--but I'm too lazy to prove right now--that having > > > the same voltages repeated symmetrically on either side of each peak > > > is critical to harmonic rejection. > > > Hmm you're suggesting that matching between equal value resistors it > > more important than hitting exact values? > > I'm suggesting the possibility, but that's only a suspicion--I showed > one example below. =A0OTOH, I also just installed a virtual caterpillar > grommet backwards in another thread. :-) > > As a practical matter, Phil's 'HC4017 with precision resistors seems > best. > > > > > > > > Where the voltage is unequal on either side, you introduce a new > > > impulse with a magnitude equal to the difference in voltages. It's > > > easy to *introduce* a 2nd harmonic component that way. =A0For example=,> > > taking the middle impulse: > > > > =A0 =A0.-----. > > > =A0 =A0| =A0 =A0 '----. > > > =A0 =A0| =A0 =A0 =A0 =A0 =A0| > > > =A0 =A0| =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > > > ___|__________|_________|__ > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 |____ =A0 =A0 | > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'----' > > > > My original thinking was to have an up/down counter, a single homemad=e> > > DAC, cycle up and down through the same (sine-weighted) values, then > > > invert (externally) for the negative swing. =A0That gets you 4x as ma=ny> > > steps and automatic symmetry, but it's not nearly as cute as Phil's > > > 4017. > > FWIW, here's what I'd imagined, where v0-v7 encode a half-wave: > > =A0 =A0 =A0 =A0 =A0'HC4051 > =A0 =A0 =A0 =A0 =A0.-----. > =A0 v7-----|0 =A0 =A0| > =A0 v6-----|1 =A0 =A0| > =A0 v5-----|2 =A0 =A0| > =A0 v4-----|3 =A0 Y|---- > =A0 v3-----|4 =A0 =A0| > =A0 v2-----|5 =A0 =A0| > =A0 v1-----|6 =A0 =A0| > =A0 v0-----|7 =A0 =A0| > =A0 =A0 =A0 =A0 =A0| ABC | > =A0 =A0 =A0 =A0 =A0'-----' > =A0 =A0 =A0 =A0 =A0 =A0||| > =A0 =A0 =A0 =A0 =A0 .---. > =A0 =A0 =A0 =A0 =A0 |XOR|<-. > =A0 =A0 =A0 =A0 =A0 '---' =A0| > =A0 =A0 =A0 =A0 =A0 =A0||| .-' > =A0 =A0 =A0 =A0 =A0 =A0||| | > =A0 =A0 =A0 =A0 =A0.------. > =A0 =A0 =A0 =A0 =A0| ABC D| > 16x clk -|> =A0 =A0 | 4-bit Counter > =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0| > =A0 =A0 =A0 =A0 =A0'------' > > This logic walks up and down through 8 voltages, which, since they are > reused from the same source, are duplicated exactly on each side of > the peak. =A0That does not guarantee symmetry about zero, though. > > Another possibility is to make v0-v7 encode a quarter-wave, then > multiply by +/-1 afterwards in analog, ensuring full symmetry.Ha, following your bipolar idea, I was wondering if I could program the 4017 for 1/2 a sine wave and use the carry output to flip a +/-1 opamp down stream. I guess that means another chip.> > Mine's three chips, minimum, to Phil's one. =A0My original goal was to > ease filtering by maximizing steps. =A0I'm not ultimately sure this is > any better w.r.t. even harmonics--that could be resistor-precision > limited...I haven't done the math.Oh don't do any math on my account. And thanks for the ideas! Doubling the number of steps doubles the clock frequency, which seems to suggest that capacitance will get you at some lower output frequency. I'm assuming that rounding off the nice sharp steps will screw things up. George H.> > -- > Cheers, > James Arthur- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -
Reply by ●October 15, 20112011-10-15
On Oct 15, 3:43=A0pm, patricia herold <pmdher...@gmail.com> wrote:> On Oct 15, 9:31=A0am, dagmargoodb...@yahoo.com wrote: > > > > > > > On Oct 14, 11:25=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > On Oct 14, 4:59=A0pm, dagmargoodb...@yahoo.com wrote: > > > > On Oct 14, 2:41=A0pm, George Herold <gher...@teachspin.com> wrote: > > > > > Hi James, =A0Yeah I was loading down the output of the 4017. =A0I=measured> > > > > an output impedance of ~180 ohms. =A0I put this number in and > > > > > recalcualted values, =A0and then selected them to ~0.1% with a DM=M. =A0The> > > > > result.... I've got all the harmonics below the 9th down by ~70dB=! =A0I> > > > > don't know how repeatable the the output imedance is? =A0I put in=a few> > > > > different 4017's and say no difference, but these were all from t=he> > > > > same order, so... > > > > > > Here's a plot from the SRS770.http://imageshack.us/photo/my-image=s/7/vco2.png/> > > > > Beautiful, and well worth the resistors, right? =A0Compared to the =cost> > > > and complexity of extra hardware, it's a bargain. > > > > > For each half-wave, I'd analyze this as the sum of three impulses, =one> > > > inside the other, added together. =A0The phasing and amplitude of t=hose> > > > impulses is critical to canceling harmonics. > > > > > =A0 =A0 =A0 =A0 .---. > > > > =A0 =A0 =A0.--' =A0 '--. > > > > =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > > > > =A0 =A0.-' =A0 =A0 =A0 =A0 '-. > > > > ___| =A0 =A0 =A0 =A0 =A0 =A0 |___ > > > > =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 | > > > > =A0 -' =A0 =A0 =A0 =A0 =A0 =A0 '- > > > > > My gut wants to say--but I'm too lazy to prove right now--that havi=ng> > > > the same voltages repeated symmetrically on either side of each pea=k> > > > is critical to harmonic rejection. > > > > Hmm you're suggesting that matching between equal value resistors it > > > more important than hitting exact values? > > > I'm suggesting the possibility, but that's only a suspicion--I showed > > one example below. =A0OTOH, I also just installed a virtual caterpillar > > grommet backwards in another thread. :-) > > > As a practical matter, Phil's 'HC4017 with precision resistors seems > > best. > > > > > Where the voltage is unequal on either side, you introduce a new > > > > impulse with a magnitude equal to the difference in voltages. It's > > > > easy to *introduce* a 2nd harmonic component that way. =A0For examp=le,> > > > taking the middle impulse: > > > > > =A0 =A0.-----. > > > > =A0 =A0| =A0 =A0 '----. > > > > =A0 =A0| =A0 =A0 =A0 =A0 =A0| > > > > =A0 =A0| =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 | > > > > ___|__________|_________|__ > > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 | =A0 =A0 =A0 =A0 | > > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 |____ =A0 =A0 | > > > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'----' > > > > > My original thinking was to have an up/down counter, a single homem=ade> > > > DAC, cycle up and down through the same (sine-weighted) values, the=n> > > > invert (externally) for the negative swing. =A0That gets you 4x as =many> > > > steps and automatic symmetry, but it's not nearly as cute as Phil's > > > > 4017. > > > FWIW, here's what I'd imagined, where v0-v7 encode a half-wave: > > > =A0 =A0 =A0 =A0 =A0'HC4051 > > =A0 =A0 =A0 =A0 =A0.-----. > > =A0 v7-----|0 =A0 =A0| > > =A0 v6-----|1 =A0 =A0| > > =A0 v5-----|2 =A0 =A0| > > =A0 v4-----|3 =A0 Y|---- > > =A0 v3-----|4 =A0 =A0| > > =A0 v2-----|5 =A0 =A0| > > =A0 v1-----|6 =A0 =A0| > > =A0 v0-----|7 =A0 =A0| > > =A0 =A0 =A0 =A0 =A0| ABC | > > =A0 =A0 =A0 =A0 =A0'-----' > > =A0 =A0 =A0 =A0 =A0 =A0||| > > =A0 =A0 =A0 =A0 =A0 .---. > > =A0 =A0 =A0 =A0 =A0 |XOR|<-. > > =A0 =A0 =A0 =A0 =A0 '---' =A0| > > =A0 =A0 =A0 =A0 =A0 =A0||| .-' > > =A0 =A0 =A0 =A0 =A0 =A0||| | > > =A0 =A0 =A0 =A0 =A0.------. > > =A0 =A0 =A0 =A0 =A0| ABC D| > > 16x clk -|> =A0 =A0 | 4-bit Counter > > =A0 =A0 =A0 =A0 =A0| =A0 =A0 =A0| > > =A0 =A0 =A0 =A0 =A0'------' > > > This logic walks up and down through 8 voltages, which, since they are > > reused from the same source, are duplicated exactly on each side of > > the peak. =A0That does not guarantee symmetry about zero, though. > > > Another possibility is to make v0-v7 encode a quarter-wave, then > > multiply by +/-1 afterwards in analog, ensuring full symmetry. > > Ha, =A0following your bipolar idea, I was wondering if I could program > the 4017 for 1/2 a sine wave and use the carry output to flip a +/-1 > opamp down stream. =A0I guess that means another chip. > > > > > Mine's three chips, minimum, to Phil's one. =A0My original goal was to > > ease filtering by maximizing steps. =A0I'm not ultimately sure this is > > any better w.r.t. even harmonics--that could be resistor-precision > > limited...I haven't done the math. > > Oh don't do any math on my account. =A0And thanks for the ideas! > Doubling the number of steps doubles the clock frequency, which seems > to suggest that capacitance will get you at some lower output > frequency. =A0I'm assuming that rounding off the nice sharp steps will > screw things up. > > George H. > > > > > > > -- > > Cheers, > > James Arthur- Hide quoted text - > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text -- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text -Opps, that wasn't my wife responding. George H.
Reply by ●October 15, 20112011-10-15
On 10/15/2011 03:51 PM, George Herold wrote:> On Oct 15, 3:43 pm, patricia herold<pmdher...@gmail.com> wrote: >> On Oct 15, 9:31 am, dagmargoodb...@yahoo.com wrote: >> >> >> >> >> >>> On Oct 14, 11:25 pm, George Herold<gher...@teachspin.com> wrote: >> >>>> On Oct 14, 4:59 pm, dagmargoodb...@yahoo.com wrote: >>>>> On Oct 14, 2:41 pm, George Herold<gher...@teachspin.com> wrote: >>>>>> Hi James, Yeah I was loading down the output of the 4017. I measured >>>>>> an output impedance of ~180 ohms. I put this number in and >>>>>> recalcualted values, and then selected them to ~0.1% with a DMM. The >>>>>> result.... I've got all the harmonics below the 9th down by ~70dB! I >>>>>> don't know how repeatable the the output imedance is? I put in a few >>>>>> different 4017's and say no difference, but these were all from the >>>>>> same order, so... >> >>>>>> Here's a plot from the SRS770.http://imageshack.us/photo/my-images/7/vco2.png/ >> >>>>> Beautiful, and well worth the resistors, right? Compared to the cost >>>>> and complexity of extra hardware, it's a bargain. >> >>>>> For each half-wave, I'd analyze this as the sum of three impulses, one >>>>> inside the other, added together. The phasing and amplitude of those >>>>> impulses is critical to canceling harmonics. >> >>>>> .---. >>>>> .--' '--. >>>>> | | >>>>> .-' '-. >>>>> ___| |___ >>>>> | | >>>>> -' '- >> >>>>> My gut wants to say--but I'm too lazy to prove right now--that having >>>>> the same voltages repeated symmetrically on either side of each peak >>>>> is critical to harmonic rejection. >> >>>> Hmm you're suggesting that matching between equal value resistors it >>>> more important than hitting exact values? >> >>> I'm suggesting the possibility, but that's only a suspicion--I showed >>> one example below. OTOH, I also just installed a virtual caterpillar >>> grommet backwards in another thread. :-) >> >>> As a practical matter, Phil's 'HC4017 with precision resistors seems >>> best. >> >>>>> Where the voltage is unequal on either side, you introduce a new >>>>> impulse with a magnitude equal to the difference in voltages. It's >>>>> easy to *introduce* a 2nd harmonic component that way. For example, >>>>> taking the middle impulse: >> >>>>> .-----. >>>>> | '----. >>>>> | | >>>>> | | | >>>>> ___|__________|_________|__ >>>>> | | >>>>> | | >>>>> |____ | >>>>> '----' >> >>>>> My original thinking was to have an up/down counter, a single homemade >>>>> DAC, cycle up and down through the same (sine-weighted) values, then >>>>> invert (externally) for the negative swing. That gets you 4x as many >>>>> steps and automatic symmetry, but it's not nearly as cute as Phil's >>>>> 4017. >> >>> FWIW, here's what I'd imagined, where v0-v7 encode a half-wave: >> >>> 'HC4051 >>> .-----. >>> v7-----|0 | >>> v6-----|1 | >>> v5-----|2 | >>> v4-----|3 Y|---- >>> v3-----|4 | >>> v2-----|5 | >>> v1-----|6 | >>> v0-----|7 | >>> | ABC | >>> '-----' >>> ||| >>> .---. >>> |XOR|<-. >>> '---' | >>> ||| .-' >>> ||| | >>> .------. >>> | ABC D| >>> 16x clk -|> | 4-bit Counter >>> | | >>> '------' >> >>> This logic walks up and down through 8 voltages, which, since they are >>> reused from the same source, are duplicated exactly on each side of >>> the peak. That does not guarantee symmetry about zero, though. >> >>> Another possibility is to make v0-v7 encode a quarter-wave, then >>> multiply by +/-1 afterwards in analog, ensuring full symmetry. >> >> Ha, following your bipolar idea, I was wondering if I could program >> the 4017 for 1/2 a sine wave and use the carry output to flip a +/-1 >> opamp down stream. I guess that means another chip. >> >> >> >>> Mine's three chips, minimum, to Phil's one. My original goal was to >>> ease filtering by maximizing steps. I'm not ultimately sure this is >>> any better w.r.t. even harmonics--that could be resistor-precision >>> limited...I haven't done the math. >> >> Oh don't do any math on my account. And thanks for the ideas! >> Doubling the number of steps doubles the clock frequency, which seems >> to suggest that capacitance will get you at some lower output >> frequency. I'm assuming that rounding off the nice sharp steps will >> screw things up. >> >> George H. >> >> >> >> >> >>> -- >>> Cheers, >>> James Arthur- Hide quoted text - >> >>> - Show quoted text -- Hide quoted text - >> >>> - Show quoted text -- Hide quoted text - >> >> - Show quoted text -- Hide quoted text - >> >> - Show quoted text - > > Opps, that wasn't my wife responding.Here we were thinking what a talented woman she must be, jumping straight in on topic like that. ;) Cheers Phil Hobbs> > George H.-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●October 15, 20112011-10-15
Phil Hobbs wrote:> > On 10/15/2011 03:51 PM, George Herold wrote: > > On Oct 15, 3:43 pm, patricia herold<pmdher...@gmail.com> wrote: > >> On Oct 15, 9:31 am, dagmargoodb...@yahoo.com wrote: > >> > >> > >> > >> > >> > >>> On Oct 14, 11:25 pm, George Herold<gher...@teachspin.com> wrote: > >> > >>>> On Oct 14, 4:59 pm, dagmargoodb...@yahoo.com wrote: > >>>>> On Oct 14, 2:41 pm, George Herold<gher...@teachspin.com> wrote: > >>>>>> Hi James, Yeah I was loading down the output of the 4017. I measured > >>>>>> an output impedance of ~180 ohms. I put this number in and > >>>>>> recalcualted values, and then selected them to ~0.1% with a DMM. The > >>>>>> result.... I've got all the harmonics below the 9th down by ~70dB! I > >>>>>> don't know how repeatable the the output imedance is? I put in a few > >>>>>> different 4017's and say no difference, but these were all from the > >>>>>> same order, so... > >> > >>>>>> Here's a plot from the SRS770.http://imageshack.us/photo/my-images/7/vco2.png/ > >> > >>>>> Beautiful, and well worth the resistors, right? Compared to the cost > >>>>> and complexity of extra hardware, it's a bargain. > >> > >>>>> For each half-wave, I'd analyze this as the sum of three impulses, one > >>>>> inside the other, added together. The phasing and amplitude of those > >>>>> impulses is critical to canceling harmonics. > >> > >>>>> .---. > >>>>> .--' '--. > >>>>> | | > >>>>> .-' '-. > >>>>> ___| |___ > >>>>> | | > >>>>> -' '- > >> > >>>>> My gut wants to say--but I'm too lazy to prove right now--that having > >>>>> the same voltages repeated symmetrically on either side of each peak > >>>>> is critical to harmonic rejection. > >> > >>>> Hmm you're suggesting that matching between equal value resistors it > >>>> more important than hitting exact values? > >> > >>> I'm suggesting the possibility, but that's only a suspicion--I showed > >>> one example below. OTOH, I also just installed a virtual caterpillar > >>> grommet backwards in another thread. :-) > >> > >>> As a practical matter, Phil's 'HC4017 with precision resistors seems > >>> best. > >> > >>>>> Where the voltage is unequal on either side, you introduce a new > >>>>> impulse with a magnitude equal to the difference in voltages. It's > >>>>> easy to *introduce* a 2nd harmonic component that way. For example, > >>>>> taking the middle impulse: > >> > >>>>> .-----. > >>>>> | '----. > >>>>> | | > >>>>> | | | > >>>>> ___|__________|_________|__ > >>>>> | | > >>>>> | | > >>>>> |____ | > >>>>> '----' > >> > >>>>> My original thinking was to have an up/down counter, a single homemade > >>>>> DAC, cycle up and down through the same (sine-weighted) values, then > >>>>> invert (externally) for the negative swing. That gets you 4x as many > >>>>> steps and automatic symmetry, but it's not nearly as cute as Phil's > >>>>> 4017. > >> > >>> FWIW, here's what I'd imagined, where v0-v7 encode a half-wave: > >> > >>> 'HC4051 > >>> .-----. > >>> v7-----|0 | > >>> v6-----|1 | > >>> v5-----|2 | > >>> v4-----|3 Y|---- > >>> v3-----|4 | > >>> v2-----|5 | > >>> v1-----|6 | > >>> v0-----|7 | > >>> | ABC | > >>> '-----' > >>> ||| > >>> .---. > >>> |XOR|<-. > >>> '---' | > >>> ||| .-' > >>> ||| | > >>> .------. > >>> | ABC D| > >>> 16x clk -|> | 4-bit Counter > >>> | | > >>> '------' > >> > >>> This logic walks up and down through 8 voltages, which, since they are > >>> reused from the same source, are duplicated exactly on each side of > >>> the peak. That does not guarantee symmetry about zero, though. > >> > >>> Another possibility is to make v0-v7 encode a quarter-wave, then > >>> multiply by +/-1 afterwards in analog, ensuring full symmetry. > >> > >> Ha, following your bipolar idea, I was wondering if I could program > >> the 4017 for 1/2 a sine wave and use the carry output to flip a +/-1 > >> opamp down stream. I guess that means another chip. > >> > >> > >> > >>> Mine's three chips, minimum, to Phil's one. My original goal was to > >>> ease filtering by maximizing steps. I'm not ultimately sure this is > >>> any better w.r.t. even harmonics--that could be resistor-precision > >>> limited...I haven't done the math. > >> > >> Oh don't do any math on my account. And thanks for the ideas! > >> Doubling the number of steps doubles the clock frequency, which seems > >> to suggest that capacitance will get you at some lower output > >> frequency. I'm assuming that rounding off the nice sharp steps will > >> screw things up. > >> > >> George H. > >> > >> > >> > >> > >> > >>> -- > >>> Cheers, > >>> James Arthur- Hide quoted text - > >> > >>> - Show quoted text -- Hide quoted text - > >> > >>> - Show quoted text -- Hide quoted text - > >> > >> - Show quoted text -- Hide quoted text - > >> > >> - Show quoted text - > > > > Opps, that wasn't my wife responding. > > Here we were thinking what a talented woman she must be, jumping > straight in on topic like that. ;)Or that he used a different name, on the weekends. ;-) -- You can't have a sense of humor, if you have no sense.
Reply by ●October 15, 20112011-10-15
On 10/15/2011 05:56 PM, Michael A. Terrell wrote:> > Phil Hobbs wrote: >> >> On 10/15/2011 03:51 PM, George Herold wrote: >>> On Oct 15, 3:43 pm, patricia herold<pmdher...@gmail.com> wrote: >>>> On Oct 15, 9:31 am, dagmargoodb...@yahoo.com wrote: >>>> >>>> >>>> >>>> >>>> >>>>> On Oct 14, 11:25 pm, George Herold<gher...@teachspin.com> wrote: >>>> >>>>>> On Oct 14, 4:59 pm, dagmargoodb...@yahoo.com wrote: >>>>>>> On Oct 14, 2:41 pm, George Herold<gher...@teachspin.com> wrote: >>>>>>>> Hi James, Yeah I was loading down the output of the 4017. I measured >>>>>>>> an output impedance of ~180 ohms. I put this number in and >>>>>>>> recalcualted values, and then selected them to ~0.1% with a DMM. The >>>>>>>> result.... I've got all the harmonics below the 9th down by ~70dB! I >>>>>>>> don't know how repeatable the the output imedance is? I put in a few >>>>>>>> different 4017's and say no difference, but these were all from the >>>>>>>> same order, so... >>>> >>>>>>>> Here's a plot from the SRS770.http://imageshack.us/photo/my-images/7/vco2.png/ >>>> >>>>>>> Beautiful, and well worth the resistors, right? Compared to the cost >>>>>>> and complexity of extra hardware, it's a bargain. >>>> >>>>>>> For each half-wave, I'd analyze this as the sum of three impulses, one >>>>>>> inside the other, added together. The phasing and amplitude of those >>>>>>> impulses is critical to canceling harmonics. >>>> >>>>>>> .---. >>>>>>> .--' '--. >>>>>>> | | >>>>>>> .-' '-. >>>>>>> ___| |___ >>>>>>> | | >>>>>>> -' '- >>>> >>>>>>> My gut wants to say--but I'm too lazy to prove right now--that having >>>>>>> the same voltages repeated symmetrically on either side of each peak >>>>>>> is critical to harmonic rejection. >>>> >>>>>> Hmm you're suggesting that matching between equal value resistors it >>>>>> more important than hitting exact values? >>>> >>>>> I'm suggesting the possibility, but that's only a suspicion--I showed >>>>> one example below. OTOH, I also just installed a virtual caterpillar >>>>> grommet backwards in another thread. :-) >>>> >>>>> As a practical matter, Phil's 'HC4017 with precision resistors seems >>>>> best. >>>> >>>>>>> Where the voltage is unequal on either side, you introduce a new >>>>>>> impulse with a magnitude equal to the difference in voltages. It's >>>>>>> easy to *introduce* a 2nd harmonic component that way. For example, >>>>>>> taking the middle impulse: >>>> >>>>>>> .-----. >>>>>>> | '----. >>>>>>> | | >>>>>>> | | | >>>>>>> ___|__________|_________|__ >>>>>>> | | >>>>>>> | | >>>>>>> |____ | >>>>>>> '----' >>>> >>>>>>> My original thinking was to have an up/down counter, a single homemade >>>>>>> DAC, cycle up and down through the same (sine-weighted) values, then >>>>>>> invert (externally) for the negative swing. That gets you 4x as many >>>>>>> steps and automatic symmetry, but it's not nearly as cute as Phil's >>>>>>> 4017. >>>> >>>>> FWIW, here's what I'd imagined, where v0-v7 encode a half-wave: >>>> >>>>> 'HC4051 >>>>> .-----. >>>>> v7-----|0 | >>>>> v6-----|1 | >>>>> v5-----|2 | >>>>> v4-----|3 Y|---- >>>>> v3-----|4 | >>>>> v2-----|5 | >>>>> v1-----|6 | >>>>> v0-----|7 | >>>>> | ABC | >>>>> '-----' >>>>> ||| >>>>> .---. >>>>> |XOR|<-. >>>>> '---' | >>>>> ||| .-' >>>>> ||| | >>>>> .------. >>>>> | ABC D| >>>>> 16x clk -|> | 4-bit Counter >>>>> | | >>>>> '------' >>>> >>>>> This logic walks up and down through 8 voltages, which, since they are >>>>> reused from the same source, are duplicated exactly on each side of >>>>> the peak. That does not guarantee symmetry about zero, though. >>>> >>>>> Another possibility is to make v0-v7 encode a quarter-wave, then >>>>> multiply by +/-1 afterwards in analog, ensuring full symmetry. >>>> >>>> Ha, following your bipolar idea, I was wondering if I could program >>>> the 4017 for 1/2 a sine wave and use the carry output to flip a +/-1 >>>> opamp down stream. I guess that means another chip. >>>> >>>> >>>> >>>>> Mine's three chips, minimum, to Phil's one. My original goal was to >>>>> ease filtering by maximizing steps. I'm not ultimately sure this is >>>>> any better w.r.t. even harmonics--that could be resistor-precision >>>>> limited...I haven't done the math. >>>> >>>> Oh don't do any math on my account. And thanks for the ideas! >>>> Doubling the number of steps doubles the clock frequency, which seems >>>> to suggest that capacitance will get you at some lower output >>>> frequency. I'm assuming that rounding off the nice sharp steps will >>>> screw things up. >>>> >>>> George H. >>>> >>>> >>>> >>>> >>>> >>>>> -- >>>>> Cheers, >>>>> James Arthur- Hide quoted text - >>>> >>>>> - Show quoted text -- Hide quoted text - >>>> >>>>> - Show quoted text -- Hide quoted text - >>>> >>>> - Show quoted text -- Hide quoted text - >>>> >>>> - Show quoted text - >>> >>> Opps, that wasn't my wife responding. >> >> Here we were thinking what a talented woman she must be, jumping >> straight in on topic like that. ;) > > > Or that he used a different name, on the weekends. ;-)You've been spending too much time in Key West. Cheers Phil Hobbs (Just back from visiting my daughter, who has an apartment a block from Bourbon Street. The difference seems to be that in the French Quarter the dives cater mostly to tourists, whereas in Key West they're for the locals!) -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●October 15, 20112011-10-15
On Sat, 15 Oct 2011 18:04:55 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 10/15/2011 05:56 PM, Michael A. Terrell wrote: >> >> Phil Hobbs wrote: >>> >>> On 10/15/2011 03:51 PM, George Herold wrote: >>>> On Oct 15, 3:43 pm, patricia herold<pmdher...@gmail.com> wrote: >>>>> On Oct 15, 9:31 am, dagmargoodb...@yahoo.com wrote: >>>>> >>>>> >>>>> >>>>> >>>>> >>>>>> On Oct 14, 11:25 pm, George Herold<gher...@teachspin.com> wrote: >>>>> >>>>>>> On Oct 14, 4:59 pm, dagmargoodb...@yahoo.com wrote: >>>>>>>> On Oct 14, 2:41 pm, George Herold<gher...@teachspin.com> wrote: >>>>>>>>> Hi James, Yeah I was loading down the output of the 4017. I measured >>>>>>>>> an output impedance of ~180 ohms. I put this number in and >>>>>>>>> recalcualted values, and then selected them to ~0.1% with a DMM. The >>>>>>>>> result.... I've got all the harmonics below the 9th down by ~70dB! I >>>>>>>>> don't know how repeatable the the output imedance is? I put in a few >>>>>>>>> different 4017's and say no difference, but these were all from the >>>>>>>>> same order, so... >>>>> >>>>>>>>> Here's a plot from the SRS770.http://imageshack.us/photo/my-images/7/vco2.png/ >>>>> >>>>>>>> Beautiful, and well worth the resistors, right? Compared to the cost >>>>>>>> and complexity of extra hardware, it's a bargain. >>>>> >>>>>>>> For each half-wave, I'd analyze this as the sum of three impulses, one >>>>>>>> inside the other, added together. The phasing and amplitude of those >>>>>>>> impulses is critical to canceling harmonics. >>>>> >>>>>>>> .---. >>>>>>>> .--' '--. >>>>>>>> | | >>>>>>>> .-' '-. >>>>>>>> ___| |___ >>>>>>>> | | >>>>>>>> -' '- >>>>> >>>>>>>> My gut wants to say--but I'm too lazy to prove right now--that having >>>>>>>> the same voltages repeated symmetrically on either side of each peak >>>>>>>> is critical to harmonic rejection. >>>>> >>>>>>> Hmm you're suggesting that matching between equal value resistors it >>>>>>> more important than hitting exact values? >>>>> >>>>>> I'm suggesting the possibility, but that's only a suspicion--I showed >>>>>> one example below. OTOH, I also just installed a virtual caterpillar >>>>>> grommet backwards in another thread. :-) >>>>> >>>>>> As a practical matter, Phil's 'HC4017 with precision resistors seems >>>>>> best. >>>>> >>>>>>>> Where the voltage is unequal on either side, you introduce a new >>>>>>>> impulse with a magnitude equal to the difference in voltages. It's >>>>>>>> easy to *introduce* a 2nd harmonic component that way. For example, >>>>>>>> taking the middle impulse: >>>>> >>>>>>>> .-----. >>>>>>>> | '----. >>>>>>>> | | >>>>>>>> | | | >>>>>>>> ___|__________|_________|__ >>>>>>>> | | >>>>>>>> | | >>>>>>>> |____ | >>>>>>>> '----' >>>>> >>>>>>>> My original thinking was to have an up/down counter, a single homemade >>>>>>>> DAC, cycle up and down through the same (sine-weighted) values, then >>>>>>>> invert (externally) for the negative swing. That gets you 4x as many >>>>>>>> steps and automatic symmetry, but it's not nearly as cute as Phil's >>>>>>>> 4017. >>>>> >>>>>> FWIW, here's what I'd imagined, where v0-v7 encode a half-wave: >>>>> >>>>>> 'HC4051 >>>>>> .-----. >>>>>> v7-----|0 | >>>>>> v6-----|1 | >>>>>> v5-----|2 | >>>>>> v4-----|3 Y|---- >>>>>> v3-----|4 | >>>>>> v2-----|5 | >>>>>> v1-----|6 | >>>>>> v0-----|7 | >>>>>> | ABC | >>>>>> '-----' >>>>>> ||| >>>>>> .---. >>>>>> |XOR|<-. >>>>>> '---' | >>>>>> ||| .-' >>>>>> ||| | >>>>>> .------. >>>>>> | ABC D| >>>>>> 16x clk -|> | 4-bit Counter >>>>>> | | >>>>>> '------' >>>>> >>>>>> This logic walks up and down through 8 voltages, which, since they are >>>>>> reused from the same source, are duplicated exactly on each side of >>>>>> the peak. That does not guarantee symmetry about zero, though. >>>>> >>>>>> Another possibility is to make v0-v7 encode a quarter-wave, then >>>>>> multiply by +/-1 afterwards in analog, ensuring full symmetry. >>>>> >>>>> Ha, following your bipolar idea, I was wondering if I could program >>>>> the 4017 for 1/2 a sine wave and use the carry output to flip a +/-1 >>>>> opamp down stream. I guess that means another chip. >>>>> >>>>> >>>>> >>>>>> Mine's three chips, minimum, to Phil's one. My original goal was to >>>>>> ease filtering by maximizing steps. I'm not ultimately sure this is >>>>>> any better w.r.t. even harmonics--that could be resistor-precision >>>>>> limited...I haven't done the math. >>>>> >>>>> Oh don't do any math on my account. And thanks for the ideas! >>>>> Doubling the number of steps doubles the clock frequency, which seems >>>>> to suggest that capacitance will get you at some lower output >>>>> frequency. I'm assuming that rounding off the nice sharp steps will >>>>> screw things up. >>>>> >>>>> George H. >>>>> >>>>> >>>>> >>>>> >>>>> >>>>>> -- >>>>>> Cheers, >>>>>> James Arthur- Hide quoted text - >>>>> >>>>>> - Show quoted text -- Hide quoted text - >>>>> >>>>>> - Show quoted text -- Hide quoted text - >>>>> >>>>> - Show quoted text -- Hide quoted text - >>>>> >>>>> - Show quoted text - >>>> >>>> Opps, that wasn't my wife responding. >>> >>> Here we were thinking what a talented woman she must be, jumping >>> straight in on topic like that. ;) >> >> >> Or that he used a different name, on the weekends. ;-) > >You've been spending too much time in Key West. > >Cheers > >Phil Hobbs > >(Just back from visiting my daughter, who has an apartment a block from >Bourbon Street. The difference seems to be that in the French Quarter >the dives cater mostly to tourists, whereas in Key West they're for the >locals!)Did you have the fried oyster po-boy at Felix's? John
