# Cross in and out

Discussion in 'General Electronics Chat' started by DexterMccoy, Mar 21, 2014.

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1. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
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Is it true that a compactor ic chip or comparator circuit is jUST a two state output either on or off. The sample and hold circuit is not just off and on states or high and low states

2. ### MrChips Moderator

Oct 2, 2009
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What do you think a sample and hold circuit should do?

Have you ever seen a HOLD button on a Fluke DMM?

3. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
The sample and hold circuit must be different because the designer choose it instead of using op amp comparator Circuit. Yes i have seen a fluke meter with the hold button, why?

4. ### MrChips Moderator

Oct 2, 2009
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5,858
The HOLD button freezes the reading at the last recorded value.

That is what a sample and hold circuit is supposed to do in your application.

5. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
Yes i know that, but is that what the circuit does that i posted?

The Sine and Cosine is the Reference voltage or the sample voltage? what is the Hold voltage?

I don't know which is the Reference voltage , it is the sine and cosine being compared to what?

6. ### kubeek Expert

Sep 20, 2005
5,516
1,061
It is a differential amplifier, so nothing is being compared, only subtracted.
There is only one input apart from the digital one which controls the switch, so what would you guess is the input that is going to be sampled?

7. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
The output of the Op amp gets feedback back to the differential input, this is the sampled voltage right?

How is it subtracted? the differential amplifier compares the reference voltage to the sample voltage and subtracts them? at a gain of 1?

8. ### MrChips Moderator

Oct 2, 2009
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A differential amplifier is another name for difference amplifier, i.e. it subtracts two signals.

Guess what a comparator does. It subtracts two signals.

9. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
So what is the difference between a comparator and a sample and hold circuit? they both subtract two signals and output the difference or a differential voltage

10. ### MrChips Moderator

Oct 2, 2009
18,471
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A comparator is not a sample and hold circuit.
A sample and hold circuit is not a comparator.
They are two different functions.

You are confusing the function of a circuit and what electronic components are used to implement that function.

It is like asking what is the difference between a filter and a capacitor.

11. ### DexterMccoy Thread Starter New Member

Feb 19, 2014
429
2
I'm not understanding the differences , they are both comparing two signals and subtracting two signals.

So what is the difference?

12. ### MrChips Moderator

Oct 2, 2009
18,471
5,858
See my post #30.