hi, i was reading about sample and hold circuits and i dint quite understand a few sentences......it said that s and h ckts are not required for low speed signals while they are of the utmost necessity for high speed circuits. can someone explain y? thanx sunil
A slow moving turtle is easy to capture. It doesn't move much and one can just run up to it and grab it. But if you try that with rabbits..You'll miss and miss and miss.. So you set out a trap (sample). Once trapped, the rabbit is 'holding' and that gives you time to do whatever.
D from BC British Columbia Canada.
Because whatever follows the sample and hold needs time to do it's job on the measurement. Most commonly, the thing following will be an ADC, and you want to (a) sample at a well-controlled point in time and (b) give the ADC time to do a conversion. A successive-approximation converter goes through several steps that need to happen when the input voltage is constant, if the input signal moves significantly during this conversion period then the measurement will be confused.
Note that life is more complicated than this: Few ADCs require sample- and-hold circuits these days. Unless you're doing something special with a special ADC chances are that the ADC has a built-in sample & hold circuit, or is a switched-capacitance type that incorporates the sample & hold function into the fabric of the A to D conversion.
-- Tim Wescott Control systems and communications consulting http://www.wescottdesign.com Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Tims very good response cut.
I am going to save questions like these for the next project I get, that says they want to take their project off-shore.
If guys like this can not figure out these functions in the classroom, what good will they be on a real project/product.
My $.02
donald
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