Definition of amp noise

In article , Richard the Dreaded Libertarian wrote: [...]

I'd bet it would cost money. The reactors will cost a lot to get rid of and we just know they are all painted with lead paint.

In article , Winfield Hill wrote: [...]

You can also use the 4051 and some resistors to supress harmonics a bit if your frequency comes from a counter.

Well now you have my curiosity. What's wrong with the sentence?

Thanks, but I thought there would be a demand for a completed lock-in amplifier chip. DSP chips are nice but that seems a little over kill for a lock-in amplifier since the DSP has to be programmed. I mean, it's an entire cpu system, right? A lock-in amplifier just doesn't seem that complicated to me. Anyway, no big deal!

You mean box unit, not a chip right? I understand that anything can be made as complex as you want. Take a function generator. There are plenty of chips that have onboard adjustable sine wave oscillators, even square and triangle waves. Yet you also purchase an entire generator that does the same thing. I'm looking at a Heathkit Function Generator IG-1271. Hey, it's old so don't laugh. It has a frequency knob from 1 - 10. It has a frequency multiplier fro 1 to 100K. It has an attenuation switch (dB)-- 50, 40, 30, 20, 10, and 0. And an output connector. That's it! Although I can buy a single chip that's probably 10 times better as far as frequency range, but it doesn't have the fancy knobs, and perhaps the 6 attenuation levels. Now isn't there a demand for lock-in phase amplifiers? Please tell me what I'm missing. Don't I need a mixer, sine wave signal, and a low pass filter? I am curious what you mean by finicky. Maybe I need a really good stable sine wave source.

Thanks for the info, Paul

It's sentences like this that make your problem a bit hard to understand.

Any DSP is a "lock-in amplifier chip."

Given that your grasp on the subject is somewhat shaky I'd abstain from trying to build a lock-in amp from scratch. When I suggested to use a "commercial" lock-in amp, I meant just that: the ready-made unit as can be bought or borrowed or stolen, whatever you prefer. None of us have the slightest clue of what you're actually trying to accomplish, but if you are associated with any kind of research facility you'll have access to such a device.

Lock-in measurements are a bit finicky at times, which makes it nice to have a commercial amp with its host of tuneable parameters, even if what you actually need is a lot simpler.

robert

On 14 Aug 2005 07:54:50 -0700, snipped-for-privacy@gmail.com wrote in Msg.

Like others have said, a 4053 can be used as a synchronous demodulator.

The principle is simple. The implementation may not be, depending on the demands of your application.

That's what I'd start with, but then I have plenty of those kicking around in the University lab where I work.

Of course there is, but they come in so many kinds and shapes that it doesn't make sense to have a one-size-fits-all chip.

Yes. The mixer can be an analog switch, or a four-quadrant multiplier. For the former, you don't need a sine wave reference, for the latter you do.

Sometimes your signal is buried so deeply in noise that you have to twirl a lot of knobs to find it, even after pushing the "set everything automatically" on a modern DSP unit. This applies mostly to meddling with the reference frequency though (to move it away from harmonics of unwanted signals) which in your case doesn't apply.

It doesn't need to be stable as much as it has to be phase-locked to your reference signal (to which you have access "by EM", whatever that means), and it needn't be sine if you use the analog- switch mixer approach.

robert

Thanks for all posts by everyone. I appreciate it *very* much! Now it's time to stop talking and start buying & build.

Electronics are amazing. Engineers are ingenious. Paul