What is the purpose of having pass gate on the power line instead of ordinary single pmos device?

Thread Starter

Vahram Hambardzumyan

Joined Jul 29, 2017
7
I want to minimize one of my schematic and looking possibilities to get rid of several single to differential converters which are actually intended to switch on/off pass gates. Can I just use pmos transistors instead of pass gates? On the power line(vdd), I think just single pmos should work, since there is no logic 0 and 1 signals there.
 

Thread Starter

Vahram Hambardzumyan

Joined Jul 29, 2017
7
Pass gates or transmission gates are devices widely used in CMOS technology to switch on/off signal lines. In my application there is a need to switch on/off power lines , not signal lines, and for that purpose I'm looking to replace those devices with pmos transistors.
 

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crutschow

Joined Mar 14, 2008
23,334
How much voltage do you want to switch?
Transmission gates typically only switch less than 15V or so.
 

Alec_t

Joined Sep 17, 2013
10,359
..... and the voltage the gate switches must lie between the gate's supply rail voltages.
 

AnalogKid

Joined Aug 1, 2013
8,103
Normally, a p-channel MOSFET is an excellent power switch. For output voltages above 20 V the gate drive circuit has to change, but not by much. This approach works up to the kilovolt range.

But for very low output voltages a p-channel device makes the circuit more complex, because now the gate has to be negative with respect to the output voltage. For example, if you want a nice solid gate drive withal of 10 V, then Vgs = -10 V, or -8.2 V with respect to the +1.8 V output. Better to use an n-channel FET, where thegate drive voltage can come from some other, higher system voltage. What other power supply voltages are available for the drive circuit?

ak
 
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