On 22.2.16 00:22, ChesterW wrote:> I need to make a mixer (a multiplier, not an adder) for sinusoid signals > somewhere between about 10 kHz and 1 Mhz. This is for a lock-in-amp. My > main constraint is low cost. I'd use a microcontroller with an A to D > and a hardware multiplier, but I'd like to keep the cost down by using a > cheaper micro. I could use a simple power-of-2 window in the micro and > then only need additions to demod, but that would give me a wider > bandwidth for noise to get in. I though a single transistor mixer design > might give better results. Anyone know of a good reference? > > ChesterW > +++ > Dr Chester Wildey > Founder MRRA Inc. > Electronic and Optoelectronic Instruments > MRI Motion, fNIRS Brain Scanners, Counterfeit and Covert Marker Detection > Fort Worth, Texas, USA > www.mrrainc.com > wildey at mrrainc dot comThe mixers today are either analog multipliers or switching mixers (which means multiplication with the oscillator signal sign only). If you do not need a perfect four-quadrant multiplication with a sine, probaly the best of today's constructions is called a Tayloe mixer (Google for it), which uses CMOS switches or multiplexers. The construction is for RF signals, but it is not difficult to adjust for lower frequencies. -- -Tauno Voipio
Single transistor mixer
Started by ●February 21, 2016
Reply by ●February 22, 20162016-02-22
Reply by ●February 22, 20162016-02-22
On 22/02/16 11:33, Tauno Voipio wrote:> On 22.2.16 00:22, ChesterW wrote: >> I need to make a mixer (a multiplier, not an adder) for sinusoid signals >> somewhere between about 10 kHz and 1 Mhz. This is for a lock-in-amp. My >> main constraint is low cost. I'd use a microcontroller with an A to D >> and a hardware multiplier, but I'd like to keep the cost down by using a >> cheaper micro. I could use a simple power-of-2 window in the micro and >> then only need additions to demod, but that would give me a wider >> bandwidth for noise to get in. I though a single transistor mixer design >> might give better results. Anyone know of a good reference? >> >> ChesterW >> +++ >> Dr Chester Wildey >> Founder MRRA Inc. >> Electronic and Optoelectronic Instruments >> MRI Motion, fNIRS Brain Scanners, Counterfeit and Covert Marker Detection >> Fort Worth, Texas, USA >> www.mrrainc.com >> wildey at mrrainc dot com > > The mixers today are either analog multipliers or switching > mixers (which means multiplication with the oscillator signal > sign only). > > If you do not need a perfect four-quadrant multiplication > with a sine, probaly the best of today's constructions is > called a Tayloe mixer (Google for it), which uses CMOS > switches or multiplexers. The construction is for RF signals, > but it is not difficult to adjust for lower frequencies.There's nothing new under the sun! That's very similar to something I built in 1979 using 4066s. It had a Q of, IIRC, 4000 at 8kHz and enabled me to detect a 1pW optical signal with a 1mm2 photodiode - which was 20dB better than competing equipment, I'm pleased to say. I "researched" the design from a 1960 paper in the Bell System Technical Journal, "An Alternative Approach to the Realization of Network Transfer Functions: The N-Path Filter" https://archive.org/details/bstj39-5-1321
Reply by ●February 22, 20162016-02-22
On a sunny day (Mon, 22 Feb 2016 13:33:44 +0200) it happened Tauno Voipio <tauno.voipio@notused.fi.invalid> wrote in <naerh6$pv3$1@dont-email.me>:>If you do not need a perfect four-quadrant multiplication >with a sine, probaly the best of today's constructions is >called a Tayloe mixer (Google for it), which uses CMOS >switches or multiplexers. The construction is for RF signals, >but it is not difficult to adjust for lower frequencies.Yep, I like this AM modulator: +5 | 100k [ ] ........ | . . audio -- |[]--------0 . C2 0-5Vpp C1 | . 0-----------||--- RF AM - filter --> | . 0 / . [ ] ..|..... 1/3 4053 / 74HC[T]4053 |100k | |control /// /// | RF square wave I also did a PAL quadrature modulator like that (4.43 MHz ) in the seventies, generated 90 degrees with a counter from an 8.86 MHz crystal. So the way this works: If no audio, then the output switches at RF frequency between 0 and 2.5 V, a 2.5 Vpp square wave. If audio is minium, at 0 V, than the output is 0 Vpp RF. And if audio is at maximum, +5V, then the output is 5 Vpp. Cannot be more perfect that that.
Reply by ●February 22, 20162016-02-22
On 22/02/2016 11:33, Tauno Voipio wrote:> On 22.2.16 00:22, ChesterW wrote: >> I need to make a mixer (a multiplier, not an adder) for sinusoid signals >> somewhere between about 10 kHz and 1 Mhz. This is for a lock-in-amp. My >> main constraint is low cost. I'd use a microcontroller with an A to D >> and a hardware multiplier, but I'd like to keep the cost down by using a >> cheaper micro. I could use a simple power-of-2 window in the micro and >> then only need additions to demod, but that would give me a wider >> bandwidth for noise to get in. I though a single transistor mixer design >> might give better results. Anyone know of a good reference? >> >> ChesterW >> +++ >> Dr Chester Wildey >> Founder MRRA Inc. >> Electronic and Optoelectronic Instruments >> MRI Motion, fNIRS Brain Scanners, Counterfeit and Covert Marker Detection >> Fort Worth, Texas, USA >> www.mrrainc.com >> wildey at mrrainc dot com > > The mixers today are either analog multipliers or switching > mixers (which means multiplication with the oscillator signal > sign only). > > If you do not need a perfect four-quadrant multiplication > with a sine, probaly the best of today's constructions is > called a Tayloe mixer (Google for it), which uses CMOS > switches or multiplexers. The construction is for RF signals, > but it is not difficult to adjust for lower frequencies. >Don't forget that all commutating mixers (and many others too) have conversion loss associated with them so if low signal levels and noise are an issue some other approach may be better - do you even need to frequency change at all? piglet
Reply by ●February 22, 20162016-02-22
On Sun, 21 Feb 2016 23:25:36 -0600, Tim Wescott <tim@seemywebsite.com> wrote:>On Sun, 21 Feb 2016 20:46:00 -0600, ChesterW wrote: >[snip]>> >> To be clear, 1 Mhz is not a requirement, I can pick the frequency. I was >> planning to look for a clean spot in the spectrum maybe around 40 kHz - >> something where I can get a reasonable over-sample on the A to D if I go >> with signal processing in an inexpensive micro. > >At 40kHz a jelly-bean op-amp for a few pennies, and John's classic* +1/-1 >circuit would almost certainly work, with whatever is cheapest for an >analog switch. > >DigiKey lists a 74VHC1GT66 at 7 cents each in qty 1000, which is pretty >cheap and should do. > >* I invented one of those when I was in grad school. I tend to invent a >lot of stuff that's been around for decades. It's trying.I used that scheme in a variety of hybrids I made at Dickson Electronics ~1972, and later, ~1980 in an FSK discriminator at OmniComp/GenRad, see Fig 5 of... <http://www.analog-innovations.com/SED/Pat-4472816.pdf> ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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 ●February 22, 20162016-02-22
On Sun, 21 Feb 2016 20:59:23 -0800 (PST), tabbypurr@gmail.com wrote:>On Monday, 22 February 2016 02:44:32 UTC, ChesterW wrote: >> On 2/21/16 5:12 PM, John Larkin wrote: > >> > A single-transistor multiplier would probably be awful. >> >> I was afraid I might hear that. > >why is it awful? > > >NTJust 'cause >:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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 ●February 22, 20162016-02-22
On Mon, 22 Feb 2016 11:50:30 +0000, Tom Gardner <spamjunk@blueyonder.co.uk> wrote:>On 22/02/16 11:33, Tauno Voipio wrote: >> On 22.2.16 00:22, ChesterW wrote: >>> I need to make a mixer (a multiplier, not an adder) for sinusoid signals >>> somewhere between about 10 kHz and 1 Mhz. This is for a lock-in-amp. My >>> main constraint is low cost. I'd use a microcontroller with an A to D >>> and a hardware multiplier, but I'd like to keep the cost down by using a >>> cheaper micro. I could use a simple power-of-2 window in the micro and >>> then only need additions to demod, but that would give me a wider >>> bandwidth for noise to get in. I though a single transistor mixer design >>> might give better results. Anyone know of a good reference? >>> >>> ChesterW >>> +++ >>> Dr Chester Wildey >>> Founder MRRA Inc. >>> Electronic and Optoelectronic Instruments >>> MRI Motion, fNIRS Brain Scanners, Counterfeit and Covert Marker Detection >>> Fort Worth, Texas, USA >>> www.mrrainc.com >>> wildey at mrrainc dot com >> >> The mixers today are either analog multipliers or switching >> mixers (which means multiplication with the oscillator signal >> sign only). >> >> If you do not need a perfect four-quadrant multiplication >> with a sine, probaly the best of today's constructions is >> called a Tayloe mixer (Google for it), which uses CMOS >> switches or multiplexers. The construction is for RF signals, >> but it is not difficult to adjust for lower frequencies. > >There's nothing new under the sun! > >That's very similar to something I built in 1979 using 4066s. >It had a Q of, IIRC, 4000 at 8kHz and enabled me to detect a >1pW optical signal with a 1mm2 photodiode - which was 20dB >better than competing equipment, I'm pleased to say. > >I "researched" the design from a 1960 paper in the Bell >System Technical Journal, "An Alternative Approach to >the Realization of Network Transfer Functions: >The N-Path Filter" > >https://archive.org/details/bstj39-5-1321I wrote a whole chapter in this book (~1964)... <http://tinyurl.com/zdu2lr6> about filtering using active filters and the N-path method (as well as mixers... <http://www.analog-innovations.com/SED/Pat-3491301.pdf> ;-) I actually implemented an N-path 455kHz IF stage using that method. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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 ●February 22, 20162016-02-22
On Sunday, February 21, 2016 at 7:28:23 PM UTC-5, mixed nuts wrote:> On 2/21/2016 5:22 PM, ChesterW wrote: > > I need to make a mixer (a multiplier, not an adder) for sinusoid signals > > somewhere between about 10 kHz and 1 Mhz. This is for a lock-in-amp. My > > main constraint is low cost. I'd use a microcontroller with an A to D > > and a hardware multiplier, but I'd like to keep the cost down by using a > > cheaper micro. I could use a simple power-of-2 window in the micro and > > then only need additions to demod, but that would give me a wider > > bandwidth for noise to get in. I though a single transistor mixer design > > might give better results. Anyone know of a good reference? > > Single diodes have been used as mixers for nearly a century. A > transistor biased near cutoff with a strong signal applied to the base > at one frequency and a weak signal at another will produce sum and > difference frequencies with some gain over a simple diode.(I'm a bit late to the discussion...) You mean a ring modulator type of thing? It would be cool (and perhaps exists) if someone made synchronous FET (analog) switches that just flipped the (output) polarity back and forth. George H.> > The conceptual information and enough math to give you a handle on > behavior are here: > > https://en.wikipedia.org/wiki/Frequency_mixer > https://en.wikipedia.org/wiki/Superheterodyne_receiver > > A CMOS exclusive-or gate (74HC86) is useable as a mixer as well. > > -- > Grizzly H.
Reply by ●February 22, 20162016-02-22
On 02/21/2016 05:22 PM, ChesterW wrote:> I need to make a mixer (a multiplier, not an adder) for sinusoid signals > somewhere between about 10 kHz and 1 Mhz. This is for a lock-in-amp. My > main constraint is low cost. I'd use a microcontroller with an A to D > and a hardware multiplier, but I'd like to keep the cost down by using a > cheaper micro. I could use a simple power-of-2 window in the micro and > then only need additions to demod, but that would give me a wider > bandwidth for noise to get in. I though a single transistor mixer design > might give better results. Anyone know of a good reference? > > ChesterWSingle transistor mixers are the pits. You can make a single-balanced one using a diff pair, e.g. a BC817DS, which at least keeps the LO out of the output to some degree. 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 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●February 22, 20162016-02-22
On 02/22/2016 12:25 AM, Tim Wescott wrote:> On Sun, 21 Feb 2016 20:46:00 -0600, ChesterW wrote: > >> On 2/21/16 5:49 PM, John Larkin wrote: >>> On Sun, 21 Feb 2016 17:23:43 -0600, Tim Wescott >>> <seemywebsite@myfooter.really> wrote: >>> >>>> On Sun, 21 Feb 2016 15:12:58 -0800, John Larkin wrote: >>>> >>>>> On Sun, 21 Feb 2016 16:22:20 -0600, ChesterW <iamsnoozin@yahoo.com> >>>>> wrote: >>>>> >>>>>> I need to make a mixer (a multiplier, not an adder) for sinusoid >>>>>> signals somewhere between about 10 kHz and 1 Mhz. This is for a >>>>>> lock-in-amp. My main constraint is low cost. I'd use a >>>>>> microcontroller with an A to D and a hardware multiplier, but I'd >>>>>> like to keep the cost down by using a cheaper micro. I could use a >>>>>> simple power-of-2 window in the micro and then only need additions >>>>>> to demod, but that would give me a wider bandwidth for noise to get >>>>>> in. I though a single transistor mixer design might give better >>>>>> results. Anyone know of a good reference? >>>>>> >>>>>> ChesterW +++ >>>>>> Dr Chester Wildey Founder MRRA Inc. >>>>>> Electronic and Optoelectronic Instruments MRI Motion, fNIRS Brain >>>>>> Scanners, Counterfeit and Covert Marker Detection Fort Worth, Texas, >>>>>> USA www.mrrainc.com wildey at mrrainc dot com >>>>> >>>>> A single-transistor multiplier would probably be awful. >>>>> >>>>> You don't need to multiply sine waves. Just multiply the signal >>>>> alternately by +1 and -1 and then lowpass filter. >>>>> >>>>> That can be done, for example, by alternately multiplexing between >>>>> SIG+ >>>>> and SIG- with a good fast analog mux. That will always have residual >>>>> errors, but could be pretty good. >>>>> >>>>> I guess the best lock-in would use a good ADC and do the multiply >>>>> digitally, in an FPGA. Noise dither maybe. >>>> >>>> With today's parts you may be able to do this with a set of fast >>>> analog switches and an op-amp. Perhaps even a 74<something fast>4051 >>>> or whatever? >>> >>> 74HC4051 would work, but the 1 MHz requirement is tricky. >>> >>> Something like FSA3157 or ADG604 or one of those T3USB gadgets might be >>> better at 1 MHz. >>> >>> The classic single-opamp +1/-1 circuit might work with a small phemt as >>> the grounding switch. >>> >>> But no single transistor! >>> >>> >> I certainly like the price of that FSA3157. >> >> To be clear, 1 Mhz is not a requirement, I can pick the frequency. I was >> planning to look for a clean spot in the spectrum maybe around 40 kHz - >> something where I can get a reasonable over-sample on the A to D if I go >> with signal processing in an inexpensive micro. > > At 40kHz a jelly-bean op-amp for a few pennies, and John's classic* +1/-1 > circuit would almost certainly work, with whatever is cheapest for an > analog switch.Lock-ins often have pretty stiff performance requirements, so that e.g. mildly asymmetrical slewing or Ron variations between the +1 and -1 arms can be a serious issue. To the OP: I gather this isn't a super-high performance application, but how good does it need to be? 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 hobbs at electrooptical dot net http://electrooptical.net
