On Oct 13, 9:32=A0pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> On 10/13/2011 07:30 PM, George Herold wrote: > > > > > > > On Oct 13, 5:13 pm, Phil Hobbs > > <pcdhSpamMeSensel...@electrooptical.net> =A0wrote: > >> 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=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 each ne=w> >>> phase. =A0(R(n) =3D 1/sin^2(n*18degrees)) > > >>> Approximate values, R0=3Dopen, R1=3DR9=3D105k, R2=3DR8=3D28.9k, R3=3D=R7=3D15.3k,> >>> R4=3DR6=3D11k, R5=3D10k. =A0all 1% resistors. > > >>> Here=92s 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=92t understand why it==92s so> >>> big. =A0Is there some way to do better than this? =A0The 9th and 11th > >>> harmonics are big and then the 19th and 21st. > > >>> Thanks George H. > > >> 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. > > >> Cheers > > >> Phil Hobbs- Hide quoted text - > > >> - Show quoted text - > > > Yeah, I was thinking about the output impedance. (I didn't looked at > > 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, excep=t> > it's only at 1kHz. > > > George H. > > Well, they come in HC too. ;)The MC claims 16 MHz, and goes to 18V (it's nice running everything off +/-15 volt supplies) Should I have ordered some HC too? George H.> > 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 -
Stepped sine wave
Started by ●October 13, 2011
Reply by ●October 13, 20112011-10-13
Reply by ●October 13, 20112011-10-13
On 10/13/2011 10:25 PM, George Herold wrote:> On Oct 13, 9:32 pm, Phil Hobbs > <pcdhSpamMeSensel...@electrooptical.net> wrote: >> On 10/13/2011 07:30 PM, George Herold wrote: >> >> >> >> >> >>> On Oct 13, 5:13 pm, Phil Hobbs >>> <pcdhSpamMeSensel...@electrooptical.net> wrote: >>>> On 10/13/2011 12:39 PM, George Herold wrote: >> >>>>> This is a continuation of the 50kHz VCO thread I started last week. I >>>>> 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). The 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. (R(n) = 1/sin^2(n*18degrees)) >> >>>>> Approximate values, R0=open, R1=R9=105k, R2=R8=28.9k, R3=R7=15.3k, >>>>> R4=R6=11k, R5=10k. all 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. I don�t understand why it�s so >>>>> big. Is there some way to do better than this? The 9th and 11th >>>>> harmonics are big and then the 19th and 21st. >> >>>>> Thanks George H. >> >>>> 50 dB is only 0.3%, which isn't too bad. That might easily be due to >>>> the output impedances of the 4017 drivers, or to the resistor >>>> tolerances. Does it get better or worse when you change VDD? If so, >>>> it's probably the output impedance. >> >>>> Cheers >> >>>> Phil Hobbs- Hide quoted text - >> >>>> - Show quoted text - >> >>> Yeah, I was thinking about the output impedance. (I didn't looked at >>> the outputs from the 4017). When I decreased the supply voltage the >>> 2nd harmonic was roughly constant while everything else went down. I >>> added a tweaker on the lowest resistance output and got everything >>> below the 9th close to 60 dB down. Which is almost beer time, except >>> it's only at 1kHz. >> >>> George H. >> >> Well, they come in HC too. ;) > > The MC claims 16 MHz, and goes to 18V (it's nice running everything > off +/-15 volt supplies) Should I have ordered some HC too? > > George H.Well, they're a fair amount faster, which means that the edge artifacts aren't as serious, and their output resistance is less, which means that the total resistance in each tap is more predictable. 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 14, 20112011-10-14
On Oct 13, 9:54=A0pm, Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:> On 10/13/2011 10:25 PM, George Herold wrote: > > > > > On Oct 13, 9:32 pm, Phil Hobbs > > <pcdhSpamMeSensel...@electrooptical.net> =A0wrote: > >> On 10/13/2011 07:30 PM, George Herold wrote: > > >>> On Oct 13, 5:13 pm, Phil Hobbs > >>> <pcdhSpamMeSensel...@electrooptical.net> =A0 =A0wrote: > >>>> 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=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 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=92s 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=92t understand why =it=92s 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. > > >>>>> Thanks George H. > > >>>> 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. > > >>>> Cheers > > >>>> Phil Hobbs- Hide quoted text - > > >>>> - Show quoted text - > > >>> 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. > > >>> George H. > > >> Well, they come in HC too. ;) > > > The MC claims 16 MHz, and goes to 18V (it's nice running everything > > off +/-15 volt supplies) =A0Should I have ordered some HC too? > > > George H. > > Well, they're =A0a fair amount faster, which means that the edge artifact=s> aren't as serious, and their output resistance is less, which means that > the total resistance in each tap is more predictable.Yes. Higher Vdd helps the CD4017 too. There's still the idea of adding a switched-cap tracking filter, running at 50f or 100f, etc. -- Cheers, James Arthur
Reply by ●October 14, 20112011-10-14
On Oct 14, 5:32=A0am, dagmargoodb...@yahoo.com wrote:> On Oct 13, 9:54=A0pm, Phil Hobbs > > > > > > <pcdhSpamMeSensel...@electrooptical.net> wrote: > > On 10/13/2011 10:25 PM, George Herold wrote: > > > > On Oct 13, 9:32 pm, Phil Hobbs > > > <pcdhSpamMeSensel...@electrooptical.net> =A0wrote: > > >> On 10/13/2011 07:30 PM, George Herold wrote: > > > >>> On Oct 13, 5:13 pm, Phil Hobbs > > >>> <pcdhSpamMeSensel...@electrooptical.net> =A0 =A0wrote: > > >>>> On 10/13/2011 12:39 PM, George Herold wrote: > > > >>>>> This is a continuation of the 50kHz VCO thread I started last wee=k. =A0I> > >>>>> tried the stepped sine wave idea as suggested by James A, and Phi=l> > >>>>> H. > > >>>>> The circuit clocks a MC14017 at 10x(F) to make a stepped sine wav=e at> > >>>>> frequency (F). =A0The ten outputs from the 4017 are sent through > > >>>>> appropriate resistors and into the summing junction of an opamp. > > >>>>> Here=92s a =91scope shot of the stepped output overlaid with a si=ne> > >>>>> wave. > > > >>>>>http://imageshack.us/photo/my-images/560/tek0024.png/ > > > >>>>> The resistor values were chosen to intersect the sine wave at eac=h new> > >>>>> phase. =A0(R(n) =3D 1/sin^2(n*18degrees)) > > > >>>>> Approximate values, R0=3Dopen, R1=3DR9=3D105k, R2=3DR8=3D28.9k, R=3=3DR7=3D15.3k,> > >>>>> R4=3DR6=3D11k, R5=3D10k. =A0all 1% resistors. > > > >>>>> Here=92s 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=92t understand wh=y it=92s so> > >>>>> big. =A0Is there some way to do better than this? =A0The 9th and =11th> > >>>>> harmonics are big and then the 19th and 21st. > > > >>>>> Thanks George H. > > > >>>> 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. > > > >>>> Cheers > > > >>>> Phil Hobbs- Hide quoted text - > > > >>>> - Show quoted text - > > > >>> 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. > > > >>> George H. > > > >> Well, they come in HC too. ;) > > > > The MC claims 16 MHz, and goes to 18V (it's nice running everything > > > off +/-15 volt supplies) =A0Should I have ordered some HC too? > > > > George H. > > > Well, they're =A0a fair amount faster, which means that the edge artifa=cts> > aren't as serious, and their output resistance is less, which means tha=t> > the total resistance in each tap is more predictable. > > Yes. =A0Higher Vdd helps the CD4017 too. > > There's still the idea of adding a switched-cap tracking filter, > running at 50f or 100f, etc.Yeah, a switched cap filter on the back side might be cool. Then the thing wouldn't be limited on the low frequency end. I've got some from another project. George H.> -- > Cheers, > James Arthur- Hide quoted text - > > - Show quoted text -
Reply by ●October 14, 20112011-10-14
On Fri, 14 Oct 2011 07:02:08 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Oct 14, 5:32�am, dagmargoodb...@yahoo.com wrote: >> On Oct 13, 9:54�pm, Phil Hobbs >> >> >> >> >> >> <pcdhSpamMeSensel...@electrooptical.net> wrote: >> > On 10/13/2011 10:25 PM, George Herold wrote: >> >> > > On Oct 13, 9:32 pm, Phil Hobbs >> > > <pcdhSpamMeSensel...@electrooptical.net> �wrote: >> > >> On 10/13/2011 07:30 PM, George Herold wrote: >> >> > >>> On Oct 13, 5:13 pm, Phil Hobbs >> > >>> <pcdhSpamMeSensel...@electrooptical.net> � �wrote: >> > >>>> On 10/13/2011 12:39 PM, George Herold wrote: >> >> > >>>>> This is a continuation of the 50kHz VCO thread I started last week. �I >> > >>>>> 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). �The 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. �(R(n) = 1/sin^2(n*18degrees)) >> >> > >>>>> Approximate values, R0=open, R1=R9=105k, R2=R8=28.9k, R3=R7=15.3k, >> > >>>>> R4=R6=11k, R5=10k. �all 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. �I don�t understand why it�s so >> > >>>>> big. �Is there some way to do better than this? �The 9th and 11th >> > >>>>> harmonics are big and then the 19th and 21st. >> >> > >>>>> Thanks George H. >> >> > >>>> 50 dB is only 0.3%, which isn't too bad. � That might easily be due to >> > >>>> the output impedances of the 4017 drivers, or to the resistor >> > >>>> tolerances. �Does it get better or worse when you change VDD? �If so, >> > >>>> it's probably the output impedance. >> >> > >>>> Cheers >> >> > >>>> Phil Hobbs- Hide quoted text - >> >> > >>>> - Show quoted text - >> >> > >>> Yeah, I was thinking about the output impedance. (I didn't looked at >> > >>> the outputs from the 4017). �When I decreased the supply voltage the >> > >>> 2nd harmonic was roughly constant while everything else went down. �I >> > >>> added a tweaker on the lowest resistance output and got everything >> > >>> below the 9th close to 60 dB down. � Which is almost beer time, except >> > >>> it's only at 1kHz. >> >> > >>> George H. >> >> > >> Well, they come in HC too. ;) >> >> > > The MC claims 16 MHz, and goes to 18V (it's nice running everything >> > > off +/-15 volt supplies) �Should I have ordered some HC too? >> >> > > George H. >> >> > Well, they're �a fair amount faster, which means that the edge artifacts >> > aren't as serious, and their output resistance is less, which means that >> > the total resistance in each tap is more predictable. >> >> Yes. �Higher Vdd helps the CD4017 too. >> >> There's still the idea of adding a switched-cap tracking filter, >> running at 50f or 100f, etc. > >Yeah, a switched cap filter on the back side might be cool. Then the >thing wouldn't be limited on the low frequency end. I've got some >from another project. > >George H. >> -- >> Cheers, >> James Arthur- Hide quoted text - >> >> - Show quoted text -It'd be trivial to make an N-path filter following a square wave, then a simple-minded smoothing R/C. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●October 14, 20112011-10-14
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 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=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 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=92s 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=92t understand why =it=92s 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 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 at > > 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, excep=t> > 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 wanna > 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, 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/ Now I've got to get it off the white proto-board and crank up the frequency. George H.
Reply by ●October 14, 20112011-10-14
On Oct 14, 11:15=A0am, Jim Thompson <To-Email-Use-The-Envelope-I...@On- My-Web-Site.com> wrote:> On Fri, 14 Oct 2011 07:02:08 -0700 (PDT), George Herold > > > > > > <gher...@teachspin.com> wrote: > >On Oct 14, 5:32=A0am, dagmargoodb...@yahoo.com wrote: > >> On Oct 13, 9:54=A0pm, Phil Hobbs > > >> <pcdhSpamMeSensel...@electrooptical.net> wrote: > >> > On 10/13/2011 10:25 PM, George Herold wrote: > > >> > > On Oct 13, 9:32 pm, Phil Hobbs > >> > > <pcdhSpamMeSensel...@electrooptical.net> =A0wrote: > >> > >> On 10/13/2011 07:30 PM, George Herold wrote: > > >> > >>> On Oct 13, 5:13 pm, Phil Hobbs > >> > >>> <pcdhSpamMeSensel...@electrooptical.net> =A0 =A0wrote: > >> > >>>> 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 throu=gh> >> > >>>>> appropriate resistors and into the summing junction of an opam=p.> >> > >>>>> 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 =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=92s the spectrum as recorded by an SRS770 spectrum analyz=er.> > >> > >>>>>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 a=nd 11th> >> > >>>>> harmonics are big and then the 19th and 21st. > > >> > >>>>> Thanks George H. > > >> > >>>> 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. > > >> > >>>> Cheers > > >> > >>>> Phil Hobbs- Hide quoted text - > > >> > >>>> - Show quoted text - > > >> > >>> Yeah, I was thinking about the output impedance. (I didn't looke=d at> >> > >>> the outputs from the 4017). =A0When I decreased the supply volta=ge the> >> > >>> 2nd harmonic was roughly constant while everything else went dow=n. =A0I> >> > >>> added a tweaker on the lowest resistance output and got everythi=ng> >> > >>> below the 9th close to 60 dB down. =A0 Which is almost beer time=, except> >> > >>> it's only at 1kHz. > > >> > >>> George H. > > >> > >> Well, they come in HC too. ;) > > >> > > The MC claims 16 MHz, and goes to 18V (it's nice running everythin=g> >> > > off +/-15 volt supplies) =A0Should I have ordered some HC too? > > >> > > George H. > > >> > Well, they're =A0a fair amount faster, which means that the edge art=ifacts> >> > aren't as serious, and their output resistance is less, which means =that> >> > the total resistance in each tap is more predictable. > > >> Yes. =A0Higher Vdd helps the CD4017 too. > > >> There's still the idea of adding a switched-cap tracking filter, > >> running at 50f or 100f, etc. > > >Yeah, a switched cap filter on the back side might be cool. =A0Then the > >thing wouldn't be limited on the low frequency end. =A0I've got some > >from another project. > > >George H. > >> -- > >> Cheers, > >> James Arthur- Hide quoted text - > > >> - Show quoted text - > > It'd be trivial to make an N-path filter following a square wave, then > a simple-minded smoothing R/C. > > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0 ...Jim Thompson> -- > | James E.Thompson, CTO =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 =A0| =A0 =A0mens =A0 =A0 |> | Analog Innovations, Inc. =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ==A0 | =A0 =A0 et =A0 =A0 =A0|> | Analog/Mixed-Signal ASIC's and Discrete Systems =A0| =A0 =A0manus =A0 ==A0|> | Phoenix, Arizona =A085048 =A0 =A0Skype: Contacts Only =A0| =A0 =A0 =A0 ==A0 =A0 =A0 |> | Voice:(480)460-2350 =A0Fax: Available upon request | =A0Brass Rat =A0| > | E-mail Icon athttp://www.analog-innovations.com| =A0 =A01962 =A0 =A0 | > > I love to cook with wine. =A0 =A0 Sometimes I even put it in the food.- H=ide quoted text -> > - Show quoted text -Hmm, not trivail for me since I have no idea what an N-path filter is. But I'm googling... George H.
Reply by ●October 14, 20112011-10-14
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 wee=k. =A0I> > > > > tried the stepped sine wave idea as suggested by James A, and Phi=l> > > > > H. > > > > > The circuit clocks a MC14017 at 10x(F) to make a stepped sine wav=e at> > > > > frequency (F). =A0The ten outputs from the 4017 are sent through > > > > > appropriate resistors and into the summing junction of an opamp. > > > > > Here=92s a =91scope shot of the stepped output overlaid with a si=ne> > > > > wave. > > > > > >http://imageshack.us/photo/my-images/560/tek0024.png/ > > > > > > The resistor values were chosen to intersect the sine wave at eac=h new> > > > > phase. =A0(R(n) =3D 1/sin^2(n*18degrees)) > > > > > > Approximate values, R0=3Dopen, R1=3DR9=3D105k, R2=3DR8=3D28.9k, R=3=3DR7=3D15.3k,> > > > > R4=3DR6=3D11k, R5=3D10k. =A0all 1% resistors. > > > > > > Here=92s 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=92t understand wh=y it=92s so> > > > > big. =A0Is there some way to do better than this? =A0The 9th and =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 d=ue to> > > > the output impedances of the 4017 drivers, or to the resistor > > > > tolerances. =A0Does it get better or worse when you change VDD? =A0=If 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 =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 wan=na> > 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 measure=d> an output impedance of ~180 ohms. =A0I put this number in and > recalcualted values, =A0and then selected them to ~0.1% with a DMM. =A0Th=e> 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? 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. 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.> Now I've got to get it off the white proto-board and crank up the > frequency. > > George H.-- Cheers, James Arthur
Reply by ●October 14, 20112011-10-14
On Fri, 14 Oct 2011 12:55:17 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Oct 14, 11:15�am, Jim Thompson <To-Email-Use-The-Envelope-I...@On- >My-Web-Site.com> wrote: >> On Fri, 14 Oct 2011 07:02:08 -0700 (PDT), George Herold >> >> >> >> >> >> <gher...@teachspin.com> wrote: >> >On Oct 14, 5:32�am, dagmargoodb...@yahoo.com wrote: >> >> On Oct 13, 9:54�pm, Phil Hobbs >> >> >> <pcdhSpamMeSensel...@electrooptical.net> wrote: >> >> > On 10/13/2011 10:25 PM, George Herold wrote: >> >> >> > > On Oct 13, 9:32 pm, Phil Hobbs >> >> > > <pcdhSpamMeSensel...@electrooptical.net> �wrote: >> >> > >> On 10/13/2011 07:30 PM, George Herold wrote: >> >> >> > >>> On Oct 13, 5:13 pm, Phil Hobbs >> >> > >>> <pcdhSpamMeSensel...@electrooptical.net> � �wrote: >> >> > >>>> On 10/13/2011 12:39 PM, George Herold wrote: >> >> >> > >>>>> This is a continuation of the 50kHz VCO thread I started last week. �I >> >> > >>>>> 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). �The 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. �(R(n) = 1/sin^2(n*18degrees)) >> >> >> > >>>>> Approximate values, R0=open, R1=R9=105k, R2=R8=28.9k, R3=R7=15.3k, >> >> > >>>>> R4=R6=11k, R5=10k. �all 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. �I don�t understand why it�s so >> >> > >>>>> big. �Is there some way to do better than this? �The 9th and 11th >> >> > >>>>> harmonics are big and then the 19th and 21st. >> >> >> > >>>>> Thanks George H. >> >> >> > >>>> 50 dB is only 0.3%, which isn't too bad. � That might easily be due to >> >> > >>>> the output impedances of the 4017 drivers, or to the resistor >> >> > >>>> tolerances. �Does it get better or worse when you change VDD? �If so, >> >> > >>>> it's probably the output impedance. >> >> >> > >>>> Cheers >> >> >> > >>>> Phil Hobbs- Hide quoted text - >> >> >> > >>>> - Show quoted text - >> >> >> > >>> Yeah, I was thinking about the output impedance. (I didn't looked at >> >> > >>> the outputs from the 4017). �When I decreased the supply voltage the >> >> > >>> 2nd harmonic was roughly constant while everything else went down. �I >> >> > >>> added a tweaker on the lowest resistance output and got everything >> >> > >>> below the 9th close to 60 dB down. � Which is almost beer time, except >> >> > >>> it's only at 1kHz. >> >> >> > >>> George H. >> >> >> > >> Well, they come in HC too. ;) >> >> >> > > The MC claims 16 MHz, and goes to 18V (it's nice running everything >> >> > > off +/-15 volt supplies) �Should I have ordered some HC too? >> >> >> > > George H. >> >> >> > Well, they're �a fair amount faster, which means that the edge artifacts >> >> > aren't as serious, and their output resistance is less, which means that >> >> > the total resistance in each tap is more predictable. >> >> >> Yes. �Higher Vdd helps the CD4017 too. >> >> >> There's still the idea of adding a switched-cap tracking filter, >> >> running at 50f or 100f, etc. >> >> >Yeah, a switched cap filter on the back side might be cool. �Then the >> >thing wouldn't be limited on the low frequency end. �I've got some >> >from another project. >> >> >George H. >> >> -- >> >> Cheers, >> >> James Arthur- Hide quoted text - >> >> >> - Show quoted text - >> >> It'd be trivial to make an N-path filter following a square wave, then >> a simple-minded smoothing R/C. >> >> � � � � � � � � � � � � � � � � � � � � ...Jim Thompson >> -- >> | James E.Thompson, CTO � � � � � � � � � � � � � �| � �mens � � | >> | Analog Innovations, Inc. � � � � � � � � � � � � | � � et � � �| >> | Analog/Mixed-Signal ASIC's and Discrete Systems �| � �manus � �| >> | Phoenix, Arizona �85048 � �Skype: Contacts Only �| � � � � � � | >> | Voice:(480)460-2350 �Fax: Available upon request | �Brass Rat �| >> | E-mail Icon athttp://www.analog-innovations.com| � �1962 � � | >> >> I love to cook with wine. � � Sometimes I even put it in the food.- Hide quoted text - >> >> - Show quoted text - > >Hmm, not trivail for me since I have no idea what an N-path filter >is. But I'm googling... > >George H.I posted several links (last month?) and a paper by Franks and Sandberg. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●October 14, 20112011-10-14
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> wrote: >> >> >> >> >> >>> 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. I >>>>> 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). The 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. (R(n) = 1/sin^2(n*18degrees)) >> >>>>> Approximate values, R0=open, R1=R9=105k, R2=R8=28.9k, R3=R7=15.3k, >>>>> R4=R6=11k, R5=10k. all 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. I don�t understand why it�s so >>>>> big. Is there some way to do better than this? The 9th and 11th >>>>> harmonics are big and then the 19th and 21st. >> >>>> 50 dB is only 0.3%, which isn't too bad. That might easily be due to >>>> the output impedances of the 4017 drivers, or to the resistor >>>> tolerances. Does it get better or worse when you change VDD? If 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). When I decreased the supply voltage the >>> 2nd harmonic was roughly constant while everything else went down. I >>> added a tweaker on the lowest resistance output and got everything >>> below the 9th close to 60 dB down. Which is almost beer time, except >>> it's only at 1kHz. >> >> I posted (and Google lost) a long post, the gist of which was: >> >> (view in fixed font) >> desired, >> G.H. desired, scaled to George's >> values theoretical 'scope actual >> (volts) (volts) (div) (div) >> 0.000 0.000 0.2 0.2 >> 0.093 0.079 0.93 1.0 >> 0.323 0.287 2.82 2.8 >> 0.577 0.545 5.17 5.2 >> 0.768 0.753 7.07 7.05 >> 0.832 0.832 7.8 7.8 >> >> (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. That's device-dependent. Might wanna >> up the resistances or switch to 'HC. >> >> The actual waveform looks pretty good. Some 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, 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/ > > Now I've got to get it off the white proto-board and crank up the > frequency. > > George H.Cool! 4017s rule--they're dead useful and just complicated enough that the anti-555 fascists don't notice. :) I use them for things like getting guaranteed break-before-make from 74HC4016-style analogue switches. Of 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 net http://electrooptical.net
