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
Single transistor mixer
Started by ●February 21, 2016
Reply by ●February 21, 20162016-02-21
In article <oMqyy.140627$OT2.139745@fx39.iad>, iamsnoozin@yahoo.com says...> > 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 comuse a DDS chip... you can simply code it from a cheap uC... That should fit your needs.. Jamie
Reply by ●February 21, 20162016-02-21
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 comA 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. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●February 21, 20162016-02-21
On Sun, 21 Feb 2016 16:22:20 -0600, 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?Assuming that your criteria are "low cost and works" then I'm not sure that you'll be happy with a single-transistor mixer. Be that as it may, stick your LO signal on the emitter and your RF signal on the base and see what comes out the collector. 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. 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. Or, look at the 1000 or so results in DigiKey's "RF mixers" section. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●February 21, 20162016-02-21
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? -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●February 21, 20162016-02-21
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! -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●February 21, 20162016-02-21
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 comFor 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). ...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 21, 20162016-02-21
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. 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 21, 20162016-02-21
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.
Reply by ●February 21, 20162016-02-21
On 2/21/16 4:48 PM, M Philbrook wrote:> In article <oMqyy.140627$OT2.139745@fx39.iad>, iamsnoozin@yahoo.com > says... >> >> 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 > > use a DDS chip... you can simply code it from a cheap uC... > > That should fit your needs.. > > Jamie >I'm OK with generating the sine wave. I need to demodulate. ChesterW
