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Design >> Analog Design >> Pass-gate behavior when switched off
https://designers-guide.org/forum/YaBB.pl?num=1249305373

Message started by skapc66 on Aug 3^rd, 2009, 6:16am

Title: Pass-gate behavior when switched off
Post by skapc66 on Aug 3^rd, 2009, 6:16am

With reference to attached picture
If I connet a voltage generator (V1) to a pass gate switched off (V2>V1) I see that the other passgate output Vx follows the input (example being V2=2V, I get Vout=1.3V if V1=1.7V and Vout=1.5V if V1=2V). Cannot understand why. Could you help?

Title: Re: Pass-gate behavior when switched off
Post by raja.cedt on Aug 3^rd, 2009, 6:47am

hi,
check the ckt properly, i think you pmos is still passing signal so please check wether you have connected proper vdd to that or not?

Thanks,
Rajasekhar.

Title: Re: Pass-gate behavior when switched off
Post by skapc66 on Aug 3^rd, 2009, 6:53am

I checked once more, all the connections are as in the picture I attached.

Rgds

Title: Re: Pass-gate behavior when switched off
Post by salty on Aug 3^rd, 2009, 8:30am

Do you have anything tied to Vx? Other that the 2 transistors?
Try this if not, put a 1MEG pulldown and see what it does.

Title: Re: Pass-gate behavior when switched off
Post by skapc66 on Aug 5^th, 2009, 11:36pm

I had an inverter input connected to Vx, but the Vx value remains the same even if I disconnect it.

Rgds

Title: Re: Pass-gate behavior when switched off
Post by raja.cedt on Aug 6^th, 2009, 12:08am

hi skapc66,
what i feel you don't see any difference in the voltage magnitude..but i am sure you could see the delay...what you do is increase the inverter size...now you feel the difference.

thanks,
rajasekhar.

Title: Re: Pass-gate behavior when switched off
Post by salty on Aug 6^th, 2009, 8:05am

Is this from a transient sim or DC sim?

Title: Re: Pass-gate behavior when switched off
Post by raja.cedt on Aug 6^th, 2009, 10:16am

hi,
ya do tran only for all digital ckts.......

thanks,
Rajasekhar.