Phil Hobbs 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!)I've never been south of Orlando. -- You can't have a sense of humor, if you have no sense.
Stepped sine wave
Started by ●October 13, 2011
Reply by ●October 15, 20112011-10-15
Reply by ●October 15, 20112011-10-15
On 10/15/2011 06:13 PM, John Larkin wrote:> 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? > > JohnNot yet. But I did get both kinds of Zatarain's Crab & Shrimp Boil and a bottle of Arnaud's remoulade. 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 net http://electrooptical.net
Reply by ●October 16, 20112011-10-16
On Oct 15, 6:13=A0pm, John Larkin <jjlar...@highNOTlandTHIStechnologyPART.com> wrote:> On Sat, 15 Oct 2011 18:04:55 -0400, Phil Hobbs > > > > > > <pcdhSpamMeSensel...@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> =A0 wrote: > >>>>> On Oct 15, 9:31 am, dagmargoodb...@yahoo.com wrote: > > >>>>>> On Oct 14, 11:25 pm, George Herold<gher...@teachspin.com> =A0 wrot=e:> > >>>>>>> On Oct 14, 4:59 pm, dagmargoodb...@yahoo.com wrote: > >>>>>>>> On Oct 14, 2:41 pm, George Herold<gher...@teachspin.com> =A0 wro=te:> >>>>>>>>> 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 =DMM. =A0The> >>>>>>>>> result.... I've got all the harmonics below the 9th down by ~70=dB! =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-ima=ges/7/vco2.png/> > >>>>>>>> Beautiful, and well worth the resistors, right? =A0Compared to t=he cost> >>>>>>>> and complexity of extra hardware, it's a bargain. > > >>>>>>>> For each half-wave, I'd analyze this as the sum of three impulse=s, one> >>>>>>>> inside the other, added together. =A0The phasing and amplitude o=f 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 -' =A0 =A0 =A0 =A0 =A0 =A0 '- > > >>>>>>>> My gut wants to say--but I'm too lazy to prove right now--that h=aving> >>>>>>>> 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 sho=wed> >>>>>> one example below. =A0OTOH, I also just installed a virtual caterp=illar> >>>>>> grommet backwards in another thread. :-) > > >>>>>> As a practical matter, Phil's 'HC4017 with precision resistors see=ms> >>>>>> 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 ex=ample,> >>>>>>>> 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 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0'----' > > >>>>>>>> My original thinking was to have an up/down counter, a single ho=memade> >>>>>>>> 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 Phi=l's> >>>>>>>> 4017. > > >>>>>> FWIW, here's what I'd imagined, where v0-v7 encode a half-wave: > > >>>>>> =A0 =A0 =A0 =A0 =A0 =A0'HC4051 > >>>>>> =A0 =A0 =A0 =A0 =A0 =A0.-----. > >>>>>> =A0 =A0 v7-----|0 =A0 =A0| > >>>>>> =A0 =A0 v6-----|1 =A0 =A0| > >>>>>> =A0 =A0 v5-----|2 =A0 =A0| > >>>>>> =A0 =A0 v4-----|3 =A0 Y|---- > >>>>>> =A0 =A0 v3-----|4 =A0 =A0| > >>>>>> =A0 =A0 v2-----|5 =A0 =A0| > >>>>>> =A0 =A0 v1-----|6 =A0 =A0| > >>>>>> =A0 =A0 v0-----|7 =A0 =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 =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 =A0 =A0 =A0 =A0 =A0| ABC D| > >>>>>> 16x clk -|> =A0 =A0 =A0 =A0| 4-bit Counter > >>>>>> =A0 =A0 =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 o=f> >>>>>> 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 prog=ram> >>>>> 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 wa=s to> >>>>>> ease filtering by maximizing steps. =A0I'm not ultimately sure thi=s 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 see=ms> >>>>> to suggest that capacitance will get you at some lower output > >>>>> frequency. =A0I'm assuming that rounding off the nice sharp steps w=ill> >>>>> 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. ;) > > >> =A0 =A0 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. =A0The 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- Hide quoted text - > > - Show quoted text -Mmmm, I was there several years ago for a March APS meeting... slurping oysters at some fine dining establishemnt (not Felix's). When we came back for the third night we were 'regulars' and 'our' waitress brought us a few raw ones each as soon as we sat down... to tide us over until she could take our order. Nothing beats a mug of beer, a plate of oysters and some of those little salty potatoes, after a long day at a trade show. George H.
Reply by ●October 16, 20112011-10-16
On Oct 15, 2:43=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.That's the "another possibility" I meant, above. The DAC only has to cover 1/4 of a sinewave, and you get the remaining wave portions by manipulating that. To wit, the external logic walks the DAC up, then down, then kicks on the analog invert (x -1) function and cycles up, then down again. Then, back to the beginning. That, here, would take about 5 chips & get you 32 samples per sinewave. So, we've got several versions: 10 steps with one chip, 16 steps with three chips, or 32 steps for five chips. Or, as always, you could use a PIC :-)> > 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.I'm not sure what capacitance you're concerned about. The CMOS doesn't care--it's fast. Stray loading on the DAC? That should be pretty trivial at these frequencies. Besides, it works in your favor, filtering out the higher-harmonics. -- Cheers, James Arthur
Reply by ●October 16, 20112011-10-16
On Oct 15, 2:51=A0pm, George Herold <gher...@teachspin.com> wrote:> 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 =DMM. =A0The> > > > > > result.... I've got all the harmonics below the 9th down by ~70=dB! =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-ima=ges/7/vco2.png/> > > > > > Beautiful, and well worth the resistors, right? =A0Compared to th=e 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 ha=ving> > > > > the same voltages repeated symmetrically on either side of each p=eak> > > > > is critical to harmonic rejection. > > > > > Hmm you're suggesting that matching between equal value resistors i=t> > > > 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 caterpill=ar> > > 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 exa=mple,> > > > > 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 hom=emade> > > > > DAC, cycle up and down through the same (sine-weighted) values, t=hen> > > > > invert (externally) for the negative swing. =A0That gets you 4x a=s 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 ar=e> > > 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 t=o> > > ease filtering by maximizing steps. =A0I'm not ultimately sure this i=s> > > 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. > >> > Opps, that wasn't my wife responding. > > George H.Well if it wasn't, for heaven's sake don't post that here! "To our wives and our girlfriends ... may they never meet."(*) --Old bachelor party toast. (*)(P.S. I first typed that as "girlfiends" -- may those especially never meet!) -- Cheers, James Arthur
Reply by ●October 16, 20112011-10-16
On Sun, 16 Oct 2011 06:25:38 -0700 (PDT), dagmargoodboat@yahoo.com wrote:>On Oct 15, 2:43�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. > >That's the "another possibility" I meant, above. The DAC only has to >cover 1/4 of a sinewave, and you get the remaining wave portions by >manipulating that. > >To wit, the external logic walks the DAC up, then down, then kicks on >the analog invert (x -1) function and cycles up, then down again. >Then, back to the beginning. > >That, here, would take about 5 chips & get you 32 samples per >sinewave. > >So, we've got several versions: 10 steps with one chip, 16 steps with >three chips, or 32 steps for five chips. Or, as always, you could use >a PIC :-)Or an 8-bit counter (e.g. '579), ROM, and DAC. 256 steps, three chips. ;-) The synchronous counter is the limitation, here.
Reply by ●October 16, 20112011-10-16
On Oct 16, 9:25=A0am, dagmargoodb...@yahoo.com wrote:> On Oct 15, 2:43=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 =DMM. =A0The> > > > > > result.... I've got all the harmonics below the 9th down by ~70=dB! =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-ima=ges/7/vco2.png/> > > > > > Beautiful, and well worth the resistors, right? =A0Compared to th=e 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 ha=ving> > > > > the same voltages repeated symmetrically on either side of each p=eak> > > > > is critical to harmonic rejection. > > > > > Hmm you're suggesting that matching between equal value resistors i=t> > > > 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 caterpill=ar> > > 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 exa=mple,> > > > > 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 hom=emade> > > > > DAC, cycle up and down through the same (sine-weighted) values, t=hen> > > > > invert (externally) for the negative swing. =A0That gets you 4x a=s 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 ar=e> > > 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. > > That's the "another possibility" I meant, above. =A0The DAC only has to > cover 1/4 of a sinewave, and you get the remaining wave portions by > manipulating that. > > To wit, the external logic walks the DAC up, then down, then kicks on > the analog invert (x -1) function and cycles up, then down again. > Then, back to the beginning. > > That, here, would take about 5 chips & get you 32 samples per > sinewave. > > So, we've got several versions: 10 steps with one chip, 16 steps with > three chips, or 32 steps for five chips. Or, as always, you could use > a PIC :-) > > > > Mine's three chips, minimum, to Phil's one. =A0My original goal was t=o> > > ease filtering by maximizing steps. =A0I'm not ultimately sure this i=s> > > 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. > > I'm not sure what capacitance you're concerned about. =A0The CMOS > doesn't care--it's fast. =A0Stray loading on the DAC? =A0That should be > pretty trivial at these frequencies. =A0Besides, it works in your favor, > filtering out the higher-harmonics.Hmm I'm not sure either, now you mention it. I guess I'm (half) thinking of the output of the summing opamp. But, that's perhaps more a slew rate issue. Anyway thanks for all the fun ideas! George H.> > -- > Cheers, > James Arthur- Hide quoted text - > > - Show quoted text -
Reply by ●October 16, 20112011-10-16
On Oct 16, 8:55=A0am, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz> wrote:> On Sun, 16 Oct 2011 06:25:38 -0700 (PDT), dagmargoodb...@yahoo.com wrote: > >On Oct 15, 2:43=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> wrot=e:> >> > > > > 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=DMM. =A0The> >> > > > > result.... I've got all the harmonics below the 9th down by ~7=0dB! =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 fro=m the> >> > > > > same order, so... > > >> > > > > Here's a plot from the SRS770.http://imageshack.us/photo/my-im=ages/7/vco2.png/> > >> > > > Beautiful, and well worth the resistors, right? =A0Compared to t=he cost> >> > > > and complexity of extra hardware, it's a bargain. > > >> > > > For each half-wave, I'd analyze this as the sum of three impulse=s, one> >> > > > inside the other, added together. =A0The phasing and amplitude o=f 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 h=aving> >> > > > 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 showe=d> >> > one example below. =A0OTOH, I also just installed a virtual caterpil=lar> >> > 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 ex=ample,> >> > > > 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 ho=memade> >> > > > 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 Phi=l'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 a=re> >> > 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. > > >That's the "another possibility" I meant, above. =A0The DAC only has to > >cover 1/4 of a sinewave, and you get the remaining wave portions by > >manipulating that. > > >To wit, the external logic walks the DAC up, then down, then kicks on > >the analog invert (x -1) function and cycles up, then down again. > >Then, back to the beginning. > > >That, here, would take about 5 chips & get you 32 samples per > >sinewave. > > >So, we've got several versions: 10 steps with one chip, 16 steps with > >three chips, or 32 steps for five chips. Or, as always, you could use > >a PIC :-) > > Or an 8-bit counter (e.g. '579), ROM, and DAC. =A0256 steps, three chips.=;-)> > The synchronous counter is the limitation, here.Hey, how about two 'HC4017's, driven out-of-phase. Clock one rising, one falling. That's 20 steps, two chips, dirt-simple. -- Cheers, James Arthur
Reply by ●October 16, 20112011-10-16
On Oct 16, 10:04=A0am, George Herold <gher...@teachspin.com> wrote:> On Oct 16, 9:25=A0am, dagmargoodb...@yahoo.com wrote: > > On Oct 15, 2:43=A0pm, patricia herold <pmdher...@gmail.com> wrote: > > > On Oct 15, 9:31=A0am, dagmargoodb...@yahoo.com wrote:> > > > 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 wil=l> > > screw things up. > > > I'm not sure what capacitance you're concerned about. =A0The CMOS > > doesn't care--it's fast. =A0Stray loading on the DAC? =A0That should be > > pretty trivial at these frequencies. =A0Besides, it works in your favor=,> > filtering out the higher-harmonics. > > Hmm I'm not sure either, now you mention it. =A0I guess I'm (half) > thinking of the output of the summing opamp. But, that's perhaps more > a slew rate issue. > > Anyway thanks for all the fun ideas!Of course. Thanks be to you for the fun puzzle, for actually doing it, and then posting back. That's fun for everyone. -- Cheers, James Arthur
Reply by ●October 16, 20112011-10-16
On Thursday, October 13, 2011 7:14:04 PM UTC-7, George Herold wrote: [about making a sine with steps set by resistor values]> resistors have to take care of the lower harmonics. (which is why the > 2nd is so disturbing) 9 or 10, 0.1% resistors are not 'out of the > question' only ~$2 + the cost of placing them. Though 1% would be > nicer.Manufacturers, take note! If one can build/sell a RAMDAC ( old video part, intended to encode colors), how about a sine-table ROMDAC? Can you beat the price of ten $2 resistors, with 8-bit output converter?
