On 2/21/16 8:39 PM, Bill Sloman wrote:
> On Monday, 22 February 2016 11:04:34 UTC+11, Jim Thompson  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
>>
>> For RF, a simple diff-pair makes an excellent mixer... think half of a
>> Gilbert multiplier (you don't need the half that eliminates DC from
>> the source... tank loads do that).
>
> The Faulkner and Harding phase sensitive detector works fine at audio frequencies as well (though it was claimed that it worked up to 30MHz).
>
> E.A.Faulkner and D.W. Harding J.Sci. Instrum. volume 43 page 97-99 (1966)
>
> http://iopscience.iop.org/article/10.1088/0950-7671/43/2/305
>
> Faulkner improved it a bit
>
> E.A.Faulkner and J.B.Grimbleby Electronic Engineering volume 39 page 565-67 (1967)
>
> Both references are from my Ph.D. thesis.
>
> The original Faulkner and Harding phase sensitive detector turned the - off-set - signal into a modulated direct current at the collector of a transistor constant current source, and fed that into a long-tailed pair of transistors whose bases were driven by the demodulating signal - ideally a pair of anti-phase square waves at the frequency of interest.
>
> The integrated difference in the currents coming out of the two collectors was the demodulated signal - an operational amplifier subtractor could refer that to 0V. I just stuck a moving coil ammeter across the collector resistors.
>
> You have to add enough voltage offset to the original AC signal to make sure that the current going into the long-tailed pair never drops to zero, and the mark-to-space ratio (which should be exactly 50%) of the demodulating drive determines how effectively this offset is rejected.
>
> It's three transistors rather than one, but it's a remarkably good circuit - even better if you used a matched transistor pair for the long-trailed pair.
>

I estimate using a sine for demod would give only about 1 dB improvement 
over square wave demod for uncorrelated noise. For correlated noise it 
should be in the neighborhood of 7 dB. I think you're right that the 
lions share of the improvement is getting out of the baseband.

My newsreader seems to have lost some of my replies to everyone. Anyway, 
thanks for the help.

ChesterW

On Wednesday, February 24, 2016 at 2:04:08 PM UTC+11, mixed nuts wrote:
> 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 

     something that is sold as

> a mixer in which 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.

It's a marketing distinction, not a technological distinction. Every four quadrant multiplier is a potential mixer, but they tend not to be sold as such.

-- 
Bill Sloman, Sydney

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.

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 com

Thanks 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

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

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

"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

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.

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?