harmonic distortion simulation for switchcap sampling n/w

Hi,

I am working on a pipelined ADC and stuck with the followng problem..
I want to simulate the input sampling network (switch cap ckt) for harmonic distortion..
Basic requirement is to compare distortion for clock voltage (for switch) of 3.3V and 2.5V..

Plz give suggestion abt the simulation based on cadance and matlab..

Thanx in advance

Re: harmonic distortion simulation for switchcap sampling n/

in my opinion,
if u only are only careing about the switch's linearity, u can build a ideal switch and then compare the result of S/H with ideal swtich to the S/H with real switch.
i think u will do FFT for the output of S/H to see any harmonic through the S/H network.

do
pss
pac
pnoise

analysis

Re: harmonic distortion simulation for switchcap sampling n/

Just extract the output (print in a file relevant points) and use Matlab for an fft.

Using Ideal source (pure sine wave) , Then run you circuit , Get the out . Then Uisng matlab do fft you can get the F1. F2. F3 . F4. F5. Then check the HD2=F2-F1, HD3=F3-F1 ...., This is SFDR simulation

Re: harmonic distortion simulation for switchcap sampling nw

Hello Frds,
I m writing down wht I did along with the simulation results..Mag of 3rd harminic is very small and acceptable but when I calculate THD value using cadence calculator, its very huge and unacceptable.. Can someone plz help me in this regard..

===============

I want to simulate the input sampling network (Sampling switch cap ckt of amplifier) for harmonic distortion..
Basic requirement is to compare distortion for clock voltage (for switch) of 3.3V and 2.5V..

Refer the simplified simulation circuit [Fig1].

Now,

1. keep the switch in "on" condition (Vg = 3.3V / 2.5V).

2. use formula

Fsignal*Nsample = Nsignal * Fsample

for

Nsample = 128 (cud be 256/512/1024...);
Nsignal = 59 (cud be any prime number 37/101) and
Fsignal = 10.1406M

I am getting Fsample = 22M

3. Run trainsient simulation for 7uS ( > 59*1/Fsignal)
Set strobepriod to some appropriate value (eg. 0.01nS)

4. Go to special function in calculator and select dft
put appropriate values in the box.. See FIg 2

{ dft(VT("/voutp")-VT("/voutm"),0n,5.81818u,65536,"Rectangular",1,1) }

where 5.81818u = 59*1/Fsignal

5. Fig 3 shows the result I got. Mag of 3rd harminic is very small and acceptable but when I calculate THD value using cadence calculator [setup shown in Fig 4], its very huge and unacceptable.. Can someone plz help me in this regard..