How to verify region of operation if the input is digital signal

[circuitking]

Hello, I want to verify in the below circuit whether Mp1b and Mn1 are in saturation. Mn3, Mn4, Mp3 and Mp4 have only digital input then how do we check for the region of operation of Mp1b and Mn1?

Image from: Study and Design of CMOS based LVDS Transmitter Mohammad Shafak Qureshi, Vidhata Poddar

 

[dick_freebird]

Some devices do not have "a" region of operation,
this is not a small signal application.

You might analyze the circuit under multiple input
conditions of interest. I'd suggest input low and input
high (per spec, @ spec common mode) and input-null
@ spec CM as three cases of interest for various
different part specs.

 

[FvM]

If we consider Vinp und Vinn as complementary logic signals with sufficient level, Mn3,4 and Mp3,4 are operated as switches and don't determine operation point of the current sources.

 

[circuitking]

If we consider Vinp und Vinn as complementary logic signals with sufficient level, Mn3,4 and Mp3,4 are operated as switches and don't determine operation point of the current sources.

Vinp und Vinn as complementary logic signals from 0 to VDD. But how do we see region of operation in Virtuoso when Mn3,4 and Mp3,4 operate as switches?

 

[Dominik Przyborowski]

LVDS TX is terminated by 100 Ohms on which swing is set to 300mV around 1.2V Common mode. So, no matter what is provided as an input, MN1 has VDS always greater than 1V, while MP1 greater than VDD-1.35, what is also usually enough.

However, if you want to see how the region of operation looks in time, simply run transient with transient operating point saved for time points of interest. How to use it, you can find in ADE help.

The simplest way is to run dc for input set both to 0 or 1 and look on dc points.