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sample and hold

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picozero

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Hi
I have to implement a sample and hold circuit. Assuming that I have to inputs :
a voltage value from a source (a photodiode) and another voltage value from another source pulsed with a delay (another photdiode). I have to compute the ration of both.

Of course their values can change during the time but their frequency no, they should behave like the signals in the second and third row of this picture:
**broken link removed**

How can I implement the hold/buffer for the first lasting enough for capturing the second one ?

How do you usually compute a "ratio" of voltage ?

Thanks in advance
 
For the sample/hold you could use a chip such as the LF398.

You can always compute the digital ratio by converting the voltages to digital with an A/D converter and use a microprocessor. To generate an analog ratio you could use a multiplier/divider chip in the divider mode. Analog Devices sells many different models.
 
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Thank you I ll look up this divider.:p

But assuming I'd like to do everything for the moment without PIC and DAC.

How can I implement a buffer with operational for the sample and hold ?
 
How can I implement a buffer with operational for the sample and hold ?
Do the photodiodes have amplifiers or are those the buffers you need?
 
I am using some photodiodes with transimpedence connected :

https://www.electro-tech-online.com/custompdfs/2011/01/getfileaspxtypepressfiletsl250r-e30.pdf

Sorry I don't know why I skimmed your answer about the LF398., thank you !

The Analog Devices devider are too expensive and I don't think the available models of tranference functions fit my purpose. I think the original advice of the DAC conversion and then operations in the digital domain ( a processor or specific IC) is better.
Thank you;)
 
I think the original advice of the DAC conversion and then operations in the digital domain ( a processor or specific IC) is better.
Thank you;)
If you use an A/D (not DAC) converter you may not need a separate sample and hold. Many A/D's include a S&H as part of their input circuitry.
 
What kind of ADC do you advice me if I have an input between 0 and 9 V and I'd like to have at least 7 bit output ?

possibly not smd and not expensive
 
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