On Wed, 24 Aug 2011 05:15:09 -0700, Bill Sloman wrote:> On Aug 24, 7:22 pm, davew <david.wo...@gmail.com> wrote: >> I'm searching for a simple one chip solution if anyone has any ideas. >> Best I've found so far might be the old 8038 function generator chip. > > If you are restricted to one chip, this is probably as good as it gets. > It distorts a triangular wave to a tolerable approximation to a sine > wave. > > You can do better by feeding a square wave through a shift register > clock at some convenient multiple of the square wave frequency, tying a > series of resistors to the outputs of the shift register and summing the > currents through the resistors into a virtual earth to produce a > staircase approximation to a sine wave, but it takes quite a long shift > register and quite a few close tolerance resistors to do better than the > 8038, and it's still a three chip solution - basically a programmable > logic device to provide the shift register and the dividers to generate > the square wave, the VCO to to generate the clock at some fairly high > multiple of the output frequency, and an op amp to sum the currents from > the resistors, plus you have to find board space for the resistors. > > The Analog Devices DDS chips do provide a very good one chip solution - > the more expensive chips include 14-bit DACs - but it isn't an analog > solution.How about a CD4040 and a bunch of resistors? (I think I mean the CD4040 -- the 4020, 4040, and 4060 are all big-ass counters, one of which has an oscillator built in). It's a ripple counter, but if you're going slow enough the clock glitches shouldn't get you too bad. -- www.wescottdesign.com
Low frequency analog VCO with sinewave output?
Started by ●August 24, 2011
Reply by ●August 24, 20112011-08-24
Reply by ●August 24, 20112011-08-24
On Aug 24, 6:24=A0pm, Tim Wescott <t...@seemywebsite.com> wrote:> On Wed, 24 Aug 2011 05:15:09 -0700, Bill Sloman wrote: > > On Aug 24, 7:22=A0pm, davew <david.wo...@gmail.com> wrote: > >> I'm searching for a simple one chip solution if anyone has any ideas. > >> Best I've found so far might be the old 8038 function generator chip. > > > If you are restricted to one chip, this is probably as good as it gets. > > It distorts a triangular wave to a tolerable approximation to a sine > > wave. > > > You can do better by feeding a square wave through a shift register > > clock at some convenient multiple of the square wave frequency, tying a > > series of resistors to the outputs of the shift register and summing th=e> > currents through the resistors into a virtual earth to produce a > > staircase approximation to a sine wave, but it takes quite a long shift > > register and quite a few close tolerance resistors to do better than th=e> > 8038, and =A0it's still a three chip solution - basically a programmabl=e> > logic device to provide the shift register and the dividers to generate > > the square wave, the VCO to to generate the clock at some fairly high > > multiple of the output frequency, and an op amp to sum the currents fro=m> > the resistors, plus you have to find board space for the resistors. > > > The Analog Devices DDS chips do provide a very good one chip solution - > > the more expensive chips include 14-bit DACs - but it isn't an analog > > solution. > > How about a CD4040 and a bunch of resistors? =A0(I think I mean the CD404=0> -- the 4020, 4040, and 4060 are all big-ass counters, one of which has an > oscillator built in). > > It's a ripple counter, but if you're going slow enough the clock glitches > shouldn't get you too bad. > > --www.wescottdesign.com- Hide quoted text - > > - Show quoted text -Thanks but I'm sticking with the analogue method in this case. Frequency stability isn't so much of a problem as I'm controlling frequency as part of a discrete PLL system.
Reply by ●August 24, 20112011-08-24
On Wed, 24 Aug 2011 02:22:29 -0700, davew wrote:> I'm searching for a simple one chip solution if anyone has any ideas. > Best I've found so far might be the old 8038 function generator chip.A PIC with a PWM output, a resistor, a cap, and a blindfold. The blindfold is to make it "analog". But why do you need it to be analog? In particular, if the 8038 is good enough, why can't a _really cruddy_ digital solution work just fine? Those old "triangle into sine" generators had really nasty glitches at the peaks of the sine waves, and I'm not even going to guess at the overall harmonic distortion (or temperature dependence thereof). Which leads to the questions: * What frequency range does it need to run in? * How good does it have to be? * How quiet does it need to be? * How linear does the command voltage vs. frequency need to be? * How close to a sine does it need to be? * Temperature range? * what other questions did I leave out? -- www.wescottdesign.com
Reply by ●August 24, 20112011-08-24
On Wed, 24 Aug 2011 10:28:45 -0700, davew wrote:> On Aug 24, 6:24 pm, Tim Wescott <t...@seemywebsite.com> wrote: >> On Wed, 24 Aug 2011 05:15:09 -0700, Bill Sloman wrote: >> > On Aug 24, 7:22 pm, davew <david.wo...@gmail.com> wrote: >> >> I'm searching for a simple one chip solution if anyone has any >> >> ideas. Best I've found so far might be the old 8038 function >> >> generator chip. >> >> > If you are restricted to one chip, this is probably as good as it >> > gets. It distorts a triangular wave to a tolerable approximation to a >> > sine wave. >> >> > You can do better by feeding a square wave through a shift register >> > clock at some convenient multiple of the square wave frequency, tying >> > a series of resistors to the outputs of the shift register and >> > summing the currents through the resistors into a virtual earth to >> > produce a staircase approximation to a sine wave, but it takes quite >> > a long shift register and quite a few close tolerance resistors to do >> > better than the 8038, and it's still a three chip solution - >> > basically a programmable logic device to provide the shift register >> > and the dividers to generate the square wave, the VCO to to generate >> > the clock at some fairly high multiple of the output frequency, and >> > an op amp to sum the currents from the resistors, plus you have to >> > find board space for the resistors. >> >> > The Analog Devices DDS chips do provide a very good one chip solution >> > - the more expensive chips include 14-bit DACs - but it isn't an >> > analog solution. >> >> How about a CD4040 and a bunch of resistors? (I think I mean the >> CD4040 -- the 4020, 4040, and 4060 are all big-ass counters, one of >> which has an oscillator built in). >> >> It's a ripple counter, but if you're going slow enough the clock >> glitches shouldn't get you too bad. >> >> --www.wescottdesign.com- Hide quoted text - >> >> - Show quoted text - > > Thanks but I'm sticking with the analogue method in this case. Frequency > stability isn't so much of a problem as I'm controlling frequency as > part of a discrete PLL system.A Wien-bridge oscillator with a couple of FETs for frequency control? An SA602 with a crystal on the oscillator port and a really well filtered VCO oscillator on the antenna port? With the right filtering that'd give you a nice clean sine wave, and a frequency range from whatever you can call "audio" right down through zero and out the other side. The VCO wouldn't need to be buffered -- the '602 doesn't _want_ much power on it's antenna port, so you could just filter the snot out of the VCO output and tap way down on the output tank circuit. As long as you feed a sine wave in on one port or the other, and stay in the chips linear range, you'll get really nice clean sine waves out. -- www.wescottdesign.com
Reply by ●August 24, 20112011-08-24
Jan Panteltje wrote:> On a sunny day (Wed, 24 Aug 2011 02:22:29 -0700 (PDT)) it happened davew > <david.wooff@gmail.com> wrote in > <aff45f3b-ff96-4d35-b3e0-d53ed85225dc@d25g2000yqh.googlegroups.com>: > >> I'm searching for a simple one chip solution if anyone has any ideas. >> Best I've found so far might be the old 8038 function generator chip. > > There was this 22?? sort of chip that does triangle and sine. > Used, it, if I only could remember the number... > :-) >I remember them. Lousy quality, the sine was approximated with a diode cicuit, which left visible artifacts.
Reply by ●August 24, 20112011-08-24
On Aug 24, 6:31=A0pm, Tim Wescott <t...@seemywebsite.com> wrote:> On Wed, 24 Aug 2011 02:22:29 -0700, davew wrote: > > I'm searching for a simple one chip solution if anyone has any ideas. > > Best I've found so far might be the old 8038 function generator chip. > > A PIC with a PWM output, a resistor, a cap, and a blindfold. > > The blindfold is to make it "analog". > > But why do you need it to be analog? =A0In particular, if the 8038 is goo=d> enough, why can't a _really cruddy_ digital solution work just fine? =A0 > Those old "triangle into sine" generators had really nasty glitches at > the peaks of the sine waves, and I'm not even going to guess at the > overall harmonic distortion (or temperature dependence thereof). > > Which leads to the questions: > > * What frequency range does it need to run in? > * How good does it have to be? > =A0 * How quiet does it need to be? > =A0 * How linear does the command voltage vs. frequency need to be? > =A0 * How close to a sine does it need to be? > * Temperature range? > * what other questions did I leave out? > > --www.wescottdesign.comI do appreciate what you are saying and don't disagree but in this application I want to do some good old fashioned mucky analogue signal processing, not PIC programming (even if I had any PIC experience).
Reply by ●August 24, 20112011-08-24
On Wed, 24 Aug 2011 20:19:01 +0200, Sjouke Burry wrote:> Jan Panteltje wrote: >> On a sunny day (Wed, 24 Aug 2011 02:22:29 -0700 (PDT)) it happened >> davew <david.wooff@gmail.com> wrote in >> <aff45f3b-ff96-4d35-b3e0-d53ed85225dc@d25g2000yqh.googlegroups.com>: >> >>> I'm searching for a simple one chip solution if anyone has any ideas. >>> Best I've found so far might be the old 8038 function generator chip. >> >> There was this 22?? sort of chip that does triangle and sine. Used, it, >> if I only could remember the number... :-) >> > I remember them. Lousy quality, the sine was approximated with a diode > cicuit, which left visible artifacts.Over a narrow range of frequencies, you can get a really nice sine wave approximation with a square wave generator and a filter, or better yet a counter, a two-bit (that's two digital bits, not $0.25) DAC, and a filter. -- www.wescottdesign.com
Reply by ●August 24, 20112011-08-24
On Aug 24, 6:57=A0pm, Tim Wescott <t...@seemywebsite.com> wrote:> On Wed, 24 Aug 2011 10:28:45 -0700, davew wrote: > > On Aug 24, 6:24=A0pm, Tim Wescott <t...@seemywebsite.com> wrote: > >> On Wed, 24 Aug 2011 05:15:09 -0700, Bill Sloman wrote: > >> > On Aug 24, 7:22=A0pm, davew <david.wo...@gmail.com> wrote: > >> >> I'm searching for a simple one chip solution if anyone has any > >> >> ideas. Best I've found so far might be the old 8038 function > >> >> generator chip. > > >> > If you are restricted to one chip, this is probably as good as it > >> > gets. It distorts a triangular wave to a tolerable approximation to =a> >> > sine wave. > > >> > You can do better by feeding a square wave through a shift register > >> > clock at some convenient multiple of the square wave frequency, tyin=g> >> > a series of resistors to the outputs of the shift register and > >> > summing the currents through the resistors into a virtual earth to > >> > produce a staircase approximation to a sine wave, but it takes quite > >> > a long shift register and quite a few close tolerance resistors to d=o> >> > better than the 8038, and =A0it's still a three chip solution - > >> > basically a programmable logic device to provide the shift register > >> > and the dividers to generate the square wave, the VCO to to generate > >> > the clock at some fairly high multiple of the output frequency, and > >> > an op amp to sum the currents from the resistors, plus you have to > >> > find board space for the resistors. > > >> > The Analog Devices DDS chips do provide a very good one chip solutio=n> >> > - the more expensive chips include 14-bit DACs - but it isn't an > >> > analog solution. > > >> How about a CD4040 and a bunch of resistors? =A0(I think I mean the > >> CD4040 -- the 4020, 4040, and 4060 are all big-ass counters, one of > >> which has an oscillator built in). > > >> It's a ripple counter, but if you're going slow enough the clock > >> glitches shouldn't get you too bad. > > >> --www.wescottdesign.com-Hide quoted text - > > >> - Show quoted text - > > > Thanks but I'm sticking with the analogue method in this case. Frequenc=y> > stability isn't so much of a problem as I'm controlling frequency as > > part of a discrete PLL system. > > A Wien-bridge oscillator with a couple of FETs for frequency control? > > An SA602 with a crystal on the oscillator port and a really well filtered > VCO oscillator on the antenna port? =A0With the right filtering that'd gi=ve> you a nice clean sine wave, and a frequency range from whatever you can > call "audio" right down through zero and out the other side. =A0The VCO > wouldn't need to be buffered -- the '602 doesn't _want_ much power on > it's antenna port, so you could just filter the snot out of the VCO > output and tap way down on the output tank circuit. =A0As long as you fee=d> a sine wave in on one port or the other, and stay in the chips linear > range, you'll get really nice clean sine waves out. > > --www.wescottdesign.com- Hide quoted text - > > - Show quoted text -Interesting ideas. From memory, doesn't the Wien-bridge oscillator need some form of amplitude stabilisation? WIll look into that one. Re the SA602 - are yousaying this would provide a solution in itself with some external filtering? Will investigate, thanks.
Reply by ●August 24, 20112011-08-24
On Wed, 24 Aug 2011 11:26:34 -0700, davew wrote:> On Aug 24, 6:57 pm, Tim Wescott <t...@seemywebsite.com> wrote: >> On Wed, 24 Aug 2011 10:28:45 -0700, davew wrote: >> > On Aug 24, 6:24 pm, Tim Wescott <t...@seemywebsite.com> wrote: >> >> On Wed, 24 Aug 2011 05:15:09 -0700, Bill Sloman wrote: >> >> > On Aug 24, 7:22 pm, davew <david.wo...@gmail.com> wrote: >> >> >> I'm searching for a simple one chip solution if anyone has any >> >> >> ideas. Best I've found so far might be the old 8038 function >> >> >> generator chip. >> >> >> > If you are restricted to one chip, this is probably as good as it >> >> > gets. It distorts a triangular wave to a tolerable approximation >> >> > to a sine wave. >> >> >> > You can do better by feeding a square wave through a shift >> >> > register clock at some convenient multiple of the square wave >> >> > frequency, tying a series of resistors to the outputs of the shift >> >> > register and summing the currents through the resistors into a >> >> > virtual earth to produce a staircase approximation to a sine wave, >> >> > but it takes quite a long shift register and quite a few close >> >> > tolerance resistors to do better than the 8038, and it's still a >> >> > three chip solution - basically a programmable logic device to >> >> > provide the shift register and the dividers to generate the square >> >> > wave, the VCO to to generate the clock at some fairly high >> >> > multiple of the output frequency, and an op amp to sum the >> >> > currents from the resistors, plus you have to find board space for >> >> > the resistors. >> >> >> > The Analog Devices DDS chips do provide a very good one chip >> >> > solution - the more expensive chips include 14-bit DACs - but it >> >> > isn't an analog solution. >> >> >> How about a CD4040 and a bunch of resistors? (I think I mean the >> >> CD4040 -- the 4020, 4040, and 4060 are all big-ass counters, one of >> >> which has an oscillator built in). >> >> >> It's a ripple counter, but if you're going slow enough the clock >> >> glitches shouldn't get you too bad. >> >> >> --www.wescottdesign.com-Hide quoted text - >> >> >> - Show quoted text - >> >> > Thanks but I'm sticking with the analogue method in this case. >> > Frequency stability isn't so much of a problem as I'm controlling >> > frequency as part of a discrete PLL system. >> >> A Wien-bridge oscillator with a couple of FETs for frequency control? >> >> An SA602 with a crystal on the oscillator port and a really well >> filtered VCO oscillator on the antenna port? With the right filtering >> that'd give you a nice clean sine wave, and a frequency range from >> whatever you can call "audio" right down through zero and out the other >> side. The VCO wouldn't need to be buffered -- the '602 doesn't _want_ >> much power on it's antenna port, so you could just filter the snot out >> of the VCO output and tap way down on the output tank circuit. As long >> as you feed a sine wave in on one port or the other, and stay in the >> chips linear range, you'll get really nice clean sine waves out. >> >> --www.wescottdesign.com- Hide quoted text - >> >> - Show quoted text - > > Interesting ideas. From memory, doesn't the Wien-bridge oscillator need > some form of amplitude stabilisation?Yes, but if you don't mind a rather distorted sine wave it can be done just by letting the output smack into the supply rails. Since you haven't responded to my questions about what you really need, one can only assume that any old wiggly line on a scope counts as a "sine" wave.> WIll look into that one. Re the > SA602 - are yousaying this would provide a solution in itself with some > external filtering? Will investigate, thanks.Yes, but you won't find it on any data sheet. You will get a clean sine wave with ease, though. -- www.wescottdesign.com
Reply by ●August 24, 20112011-08-24
On Wed, 24 Aug 2011 11:20:54 -0700, davew wrote:> On Aug 24, 6:31 pm, Tim Wescott <t...@seemywebsite.com> wrote: >> On Wed, 24 Aug 2011 02:22:29 -0700, davew wrote: >> > I'm searching for a simple one chip solution if anyone has any ideas. >> > Best I've found so far might be the old 8038 function generator chip. >> >> A PIC with a PWM output, a resistor, a cap, and a blindfold. >> >> The blindfold is to make it "analog". >> >> But why do you need it to be analog? In particular, if the 8038 is >> good enough, why can't a _really cruddy_ digital solution work just >> fine? Those old "triangle into sine" generators had really nasty >> glitches at the peaks of the sine waves, and I'm not even going to >> guess at the overall harmonic distortion (or temperature dependence >> thereof). >> >> Which leads to the questions: >> >> * What frequency range does it need to run in? * How good does it have >> to be? >> * How quiet does it need to be? >> * How linear does the command voltage vs. frequency need to be? * >> How close to a sine does it need to be? >> * Temperature range? >> * what other questions did I leave out? >> >> --www.wescottdesign.com > > I do appreciate what you are saying and don't disagree but in this > application I want to do some good old fashioned mucky analogue signal > processing, not PIC programming (even if I had any PIC experience).If you cough up answers to my questions on what you really need, folks will be able to give you more specific help. I understand not wanting to break the digital barrier -- I tend to cross that particular Rubicon with ease, yet I have circuits out there that are all analog, or that only use "digital" parts in an analog way. -- www.wescottdesign.com
