Passive f to 2f converter

Transformer saturating? Try using a higher impedance transformer.

Another cute way: drive an optoisolator that has back-to-back LEDs, and use a pullup on the phototransistor. You'll get two sinks per cycle.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

Hmm I don't really know. Here's a 'scope shot of the input to the transformer.

At a slightly higher frequency the step and the jaggedies go away. (Jaggedies look like slew rate limitied oscillations ~2MHz.)

I put 100 ohms between the opamp and transformer and that made everyone happy.

Of course this is much below the spec for the transformer. (200 to 15 kHz.)

se a

Oh that's nice, then I wouldn't need the transformer. Any hints for an opto-isolater with back to back leds? I see nothing useful in digikeys search function.

George H.

.highlandtechnology.com  jlarkin at highlandtechnology dot com

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H11AA1, AA2, AA3, AND AA4, but why bother when you can do the same 
thing by feeding a single emitter device from a full-wave bridge? 

.       +-----+    +-------------+ 
.AC>----|~   +|----|A---+        | 
.       |     |    |    |       C|   
.       |     |    |  [LED]-> B  | 
.       |     |    |    |       E|  
.AC>----|~   -|----|K---+        | 
.       +-----+    +-------------+

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Thanks John, If I can do it without the brdige and transformer that will be a win.

I've got a single ended (is that the right term?) input and output. (Both are referenced to the same ground point.) So I like the double LED idea. I don't have that much voltage to play with (~ 6 V p-p). I guess I'll loose about the same on the LED's or bridge.

Oh, but I'll need some voltage to drive the transistor.... but maybe I can use that idea sometime in the future.

George H.

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Hey, is there an opto with back to back LEDs and just a photodiode output?

Or maybe a dual, that I hook up back to back? I found this on digikey... a bit spendie

But a lot less mass than a transformer!

George H.

We use this one:

What's your signal waveform? What 2f waveform do you need? A true sine-to-sine doubler is an analog squarer and a DC offset.

--

John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    

Precision electronic instrumentation 
Picosecond-resolution Digital Delay and Pulse generators 
Custom timing and laser controllers 
Photonics and fiberoptic TTL data links 
VME  analog, thermocouple, LVDT, synchro, tachometer 
Multichannel arbitrary waveform generators

use a

--
Here's the data sheet: 

http://www.irf.com/product-info/datasheets/data/pvi5013r.pdf 

Take a look at the response time specs... 

OTOH, take a look at this: 

http://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/H11F1,2,3.pdf 

Wire the LEDs in parallel opposition and the FETs in parallel and 
Bob's yer uncle!

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OK thanks,

-sine

The input is a sine wave 3-3kHz, ~6Vp-p. The output can be almost anything that has some 2f. The user can send the signal through a filter (with gain = to Q) and then the signal becomes the reference input for a switched gain lockin amp.

George H.

.highlandtechnology.com  jlarkin at highlandtechnology dot com

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Ughh, that is slow. 1 uA into ~200pF, and with Vf= 8V, that's more than 1nC so sure more than 1ms response time.... but maybe I can reduce the load resistance (and forward voltage) and make it a bit snappier?

Very interesting. I like the circuit apps! But I'll need power to turn the FET on. (not impossible, but not ideal either.)

Thanks George H.

sine-to-sine

--- Try this:

+------------------+ F1>---[R]---+--|---+ +----|----+ | | |A | | | | | [LED]-> [MOSFET] | | | | | | | | F1>-------+-|--|---+ +----|--+ | | | +------------------+ | | | | | | | | +------------------+ | | | +--|---+ +----|--|-+-->F2 | | |K | | | | | [LED]-> [MOSFET] | +---->GND | | | | | | +----|---+ +----|--| | +------------------+ | +--------------------------+ | GND

The solid state relays are:

$file/Pla160.pdf

and they're in stock at Mouser:

for USD 3.61

-- JF

module.

was

transformer.

and use a

--
Well, if push came to shove you could build one by shining a couple of 
high-intensity LEDs operating off of your low-current signal source 
onto a phototransistor and using the CE junction like a resistor.

Hi, George. I don't have an answer to your question, but I'm just curious if lock-in designs have finally evolved since the 80's/90's to allow the reference oscillator to drive the multiplier (or whatever) directly. Back then, every model I could track down had the reference oscillator as pretty much a tacked-on free-standing circuit; the multiplier was *only* driven by the PLL. So if you wanted to apply a frequency step, you had to apply a step to the VCO, which was plumbed to the PLL, and wait for the PLL to settle.

But the PLL is really only needed for cases where you *must* use an external reference... the classic case being a "fan blade" optical chopper, where the frequency was determined by the motor speed.

I imagine *somebody* still uses this arrangement, but in my case (hearing research) and plenty of others, what people really needed was simply a reference oscillator to drive their experiment *and* the lock-in multiplier to analyze the signal coming back from the experiment. No need for a PLL, since the reference oscillator can be a quadrature type right from the get-go (digital, these days), and everything is always "locked"... no waiting for the PLL.

The solution for me was to go with synchronous waveform averaging, which has other benefits as well (like preserving a complex neural response waveform). But lock-ins would still have an edge in absolute S/N for those who deal with single response frequencies. So, can you now skip the PLL if you want to?

Best regards,

Bob Masta DAQARTA v7.10 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, Pitch Track, Pitch-to-MIDI FREE Signal Generator, DaqMusic generator Science with your sound card!

Hi Bob, I have very little idea of what 'modern' lockin design looks like. (I'd be tempted to guess that lots is now done in software.)

The lockin we sell is a throw-back. It's basically for students to follow the signal chain through the insturment. It's has no PLL inside it. (Gasp)

There are two classes of lockin's that I know of. One uses the multiplier function to mix the signal with the reference. And the other uses a switched gain stage. The lockin we sell uses the switched gain stage topology. It's built around the AD630 chip. So sure it's possible to do a lockin w/o a PLL... the switched gain stage approach just needs a comparator to sense the zero crossing. With a quadrature oscillator (and two swithced gain stages) you wouldn't even need a phase shifter. Signal changes could be as fast as the final low pass filter. (The down side of the switched gain is that it also sees signals (or noise) at odd harmonics of the reference frequency.)

My favorite lockin from grad school was the 124A from EG&G. I was talking with the design engineer from SRS at a trade show a year or two ago and he has redone the 124A for SRS. I think it's an 'all- analog' signal chain. I hear that the low temperature guys like that, because the digital based lockin's would send 'crud' back down into their cryostat's and screw things up.

George H.

and use a

to-sine

The use of an analog multiplier (the six-transistor kind, like in MC1496) will get it done without the (circa 4mA) current requirement of an LED solution. It 's easy to drive a center-tapped transformer with the output. Of course, this is NOT a passive solution, it takes a power supply; the ups ide, is that you can bias it for 2 uA current draw and toss two in more AA cells ea ch year. It's sensitive to level, you'd want an input attenuator, too.