frequency responce of sample & hold circuit

[houly]

Hello all
I would want to know what is the frequency response of a Sample&Hold circuit ?
How can I know H(f) expression ?

Thanks for your help

 

[LvW]

Hello all
I would want to know what is the frequency response of a Sample&Hold circuit ?
How can I know H(f) expression ?

Thanks for your help

The transfer function is

H(s)=(1-exp(s*Ts))/s*Ts with Ts=sampling time.

 

[glias]

Thanks
in fact I want to know how they could write this H(f) on page 18 (**broken link removed**). They said that the frequency respons eof the S&H is a sin(f)/f where does it come from ?

 

[LvW]

If you replace s by jw in the formula which I gave you before, you will get, indeed, a sin(f)/f response. Try it.

 

[glias]

Sorry I don't see...
s means freq. domain, I don't understand why the replacement of s to jw could help me. For me "jw" and "s" and "f" variables are same, they indicate frequency domain is that right ?

I have H(jw)=Ts*(1-e(jw*Ts))/jw ... = sin(f)/f ?

 

[LvW]

OK, here is the way:

H(s)=(1-exp(s*Ts))/s*Ts

* replace s by jw
* Multiply numerator and denumerator with exp(jw*Ts/2)
* Apply EULER's formula for complex numbers to transfer the exponential function into a trigonometric function (sinus).
*This results in the expression

A(jw)=|A(x)|*exp(-j*x) with |A(x)|=sin(x)/x and x=w*Ts/2.

Thus, you have a sinx/x function with phase shift.

 

[LvW]

Correction:

H(s)=(1-exp(-s*Ts))/s*Ts

 

[glias]

OK ! I understand better, thanks a lot for your help and for the correction