In article <kEuyy.24532$UV.20168@fx29.iad>, iamsnoozin@yahoo.com says...> > > Do you need something that gives an output down to DC, without bias? If > > so, you're going to be vastly unhappy with a single-transistor mixer. > > I'm assuming you mean does the input signal need to go down to DC. No. > To be clear, I'm generating the carrier and running it through the DUT, > then recovering the modified signal and demodulating it using the > carrier. I can pick the carrier to be anything I want within reason. It > might be nice to give the system the smarts to scan for a clean spot in > the spectrum and change the carrier accordingly, but certainly no need > to do anything but demodulate at whatever frequency is used to probe. > > > > > Check out the SA602. It's so old it creaks, but it works and with the > > right signal conditioning on its outputs it gives a fairly decent output > > down to DC. > > It's too expensive. Also I'd be afraid of it going obsolete. My > benchmark for cost right now is a dsPic at around $1.60. It has a > hardware multiplier and so I could do a pretty good demod inside the > chip. So the idea is to try to get rid of the need for the multiplier by > using an analog multiplier, thus enabling the use of a more modest micro. > > > > > Or, look at the 1000 or so results in DigiKey's "RF mixers" section. > > > > > > ChesterW >Looks like you are doing some sort of side band modulation demodulatio etct.... I guess the carrier freq could be what ever, as long as you use the same one in decoding. I remember using the LM1496, double balance mixer..gibert cell. you can also use 4 diodes, ring diode mixer.. couple of op-amps from a dual supply to form the bridge. Jamie
Single transistor mixer
Started by ●February 21, 2016
Reply by ●February 22, 20162016-02-22
Reply by ●February 22, 20162016-02-22
On Monday, February 22, 2016 at 7:10:23 PM UTC-5, Phil Hobbs wrote:> John's bottom one is generally best unless you can edit out the slew artifacts. An HC4017 or the PLD/FPGA/uP equivalent can turn off the integration during the teansients, which is generally a win. > > Cheers > > Phil HobbsThanks, (I know we've talked about his before.. I've got these DG611's in my part draw...(DIPs)... waiting.) I guess my mind went to the top circuit first. I drew something like the bottom one, but with an opamp in the top line... So many circuits, so little time... George H. (I'm trying to finish a digital thing... not my favorite.)
Reply by ●February 23, 20162016-02-23
On 22/02/2016 22:22, ChesterW wrote:> Sounds interesting. I sent off my $33 today. They said I could download > the paper .... on Thursday! Haven't the Brits discovered the internet > yet :) > > ChesterWIf you can't wait to Thursday you can search for patents in their names, they patented several variants of the p.d. in the late 1960s early 1970s - all GB as I recall. piglet
Reply by ●February 23, 20162016-02-23
On 02/22/2016 10:45 AM, Jim Thompson wrote:> 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/bstj39-5-1321 > > I 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 >Bargain! Random tangential question: Is there any technical reason that one couldn't design an IC OTA in the vein of the CA3080/LM13700 that has a much higher bandwidth, into the 50-100MHz range?
Reply by ●February 23, 20162016-02-23
On Tue, 23 Feb 2016 14:07:42 -0500, bitrex <bitrex@de.lete.earthlink.net> wrote:>On 02/22/2016 10:45 AM, Jim Thompson wrote: >> 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/bstj39-5-1321 >> >> I 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 >> > >Bargain! > >Random tangential question: Is there any technical reason that one >couldn't design an IC OTA in the vein of the CA3080/LM13700 that has a >much higher bandwidth, into the 50-100MHz range?Perhaps in a modern BiCMOS process. ...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 23, 20162016-02-23
"bitrex" <bitrex@de.lete.earthlink.net> wrote in message news:262zy.1489$nO2.155@fx41.iad...> Random tangential question: Is there any technical reason that one > couldn't design an IC OTA in the vein of the CA3080/LM13700 that has a > much higher bandwidth, into the 50-100MHz range?Nope! http://www.ti.com/lit/ds/symlink/opa860.pdf And if you really need to spend money: http://www.analog.com/media/en/technical-documentation/data-sheets/AD835.pdf Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: http://seventransistorlabs.com
Reply by ●February 23, 20162016-02-23
On Monday, February 22, 2016 at 4:51:49 PM UTC+11, mixed nuts wrote:> On 2/21/2016 9:47 PM, ChesterW wrote: > > On 2/21/16 6:52 PM, whit3rd wrote: > >> On Sunday, February 21, 2016 at 2:22:18 PM UTC-8, ChesterW wrote: > >>> I need to make a mixer (a multiplier, not an adder) ... for a > >>> lock-in-amp. > >> > >> The classic one-transisor mixer is a dual-gate MOSFET. > >> If your 'lock-in amp' has a squarewave reference, analog-switch > >> polarity reversal can be very effective, too. The 'switch' elements > >> can be diodes, or FETs, or any other kind of transistor; you could > >> even consider photocouplers, at your relatively low frequency > >> range. > >> > > I've never heard of a dual-gate mixer, so thanks for the tip! > > > > In an ideal world I'll use a sine wave for my carrier and demodulate > > with a sine. That way my noise bandwidth will be lower I think than > > using a square wave. > > > > My DUT doesn't give a linear response to a square wave, but does to a > > sine wave. The carrier used to demod the signal can be thought of as a > > sort of matched filter, so since my signal is a sine the best demod > > carrier is also a sine. > > Mixers are always driven with a square wave local oscillator to > guarantee linear response to the signal and eliminate LO amplitude > variations as a factor.They aren't. If the amplitude of the local sine wave oscillator is stable - which can be arranged - there aren't any local oscillator amplitude variations, and people who are worried about detecting odd harmonic content in the signal they are looking at do go to the trouble of building clean and stable sine wave local oscillators. -- Bill Sloman, Sydney
Reply by ●February 23, 20162016-02-23
On 2/22/16 11:19 AM, John Larkin wrote:> On Mon, 22 Feb 2016 12:03:39 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> 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 > > There are at least three ways to do the basic +-1 thing... > > https://dl.dropboxusercontent.com/u/53724080/Circuits/Plus_Minus_Mixer.JPG > > All have interesting charge injection issues. Some opamps go nuts if > you switch at their inputs, or outputs. > > A really good analog lockin is hard to do. > >Nice. Thanks. Looks like 2011 was a good year for lock-in amps. ChesterW
Reply by ●February 23, 20162016-02-23
On 2/21/16 4:22 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? > > 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 comThanks everyone for your generosity in time and solutions. The customer is willing, so I plan to do everything in the micro - generate the carrier, digitize the signals and do the demod and filtering. They can pay me to reduce cost by designing some analog circuitry that needs only a cheaper micro later if they want. ChesterW
Reply by ●February 23, 20162016-02-23
On 2/23/2016 7:52 PM, bill.sloman@ieee.org wrote:> On Monday, February 22, 2016 at 4:51:49 PM UTC+11, mixed nuts wrote: >> On 2/21/2016 9:47 PM, ChesterW wrote: >>> On 2/21/16 6:52 PM, whit3rd wrote: >>>> On Sunday, February 21, 2016 at 2:22:18 PM UTC-8, ChesterW >>>> wrote: >>>>> I need to make a mixer (a multiplier, not an adder) ... for >>>>> a lock-in-amp. >>>> >>>> The classic one-transisor mixer is a dual-gate MOSFET. If your >>>> 'lock-in amp' has a squarewave reference, analog-switch >>>> polarity reversal can be very effective, too. The 'switch' >>>> elements can be diodes, or FETs, or any other kind of >>>> transistor; you could even consider photocouplers, at your >>>> relatively low frequency range. >>>> >>> I've never heard of a dual-gate mixer, so thanks for the tip! >>> >>> In an ideal world I'll use a sine wave for my carrier and >>> demodulate with a sine. That way my noise bandwidth will be lower >>> I think than using a square wave. >>> >>> My DUT doesn't give a linear response to a square wave, but does >>> to a sine wave. The carrier used to demod the signal can be >>> thought of as a sort of matched filter, so since my signal is a >>> sine the best demod carrier is also a sine. >> >> Mixers are always driven with a square wave local oscillator to >> guarantee linear response to the signal and eliminate LO amplitude >> variations as a factor. > > They aren't. If the amplitude of the local sine wave oscillator is > stable - which can be arranged - there aren't any local oscillator > amplitude variations, and people who are worried about detecting odd > harmonic content in the signal they are looking at do go to the > trouble of building clean and stable sine wave local oscillators.I know that, but try to find a mixer that conversion gain, IIP3 and NF depend significantly on LO power. They put limiters in 'em and tell you feed 'em with enough voltage to make things nice and square. If you want a linear multiplier, you make or buy a multiplier. I think it was an ADI app note (or dialog article) where that distinction was made by Barry Gilbert and Bob Clarke. -- Grizzly H.
