Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

How to calculate input common mode voltage of comparator in normal mode


Newbie level 6
Nov 4, 2021
Reaction score
Trophy points
Activity points
Hello Everyone,
I want to know how to find Input common mode voltage and input common mode rejection ratio of comparator? Can anyone provide me step by step procedure?
Thanks in Advance
The input common mode voltage is something you can measure
(or assert). (VIN+ + VIN-)/2. It is what it is, depending on signal

Common mode input -range- is another matter. There will be
different ranges for damage, functional, pristine analog
operation. A product would spec the last, as product electrical
performance table conditions. To find it you would characterize
every "care-about" across an over-the-top common mode input
range and see where things start to fall apart - then back off by
some "feels right" margin for luck in production.

CMRR for a comparator, I would not use but you can measure by
using a classic op amp test loop and let the comparator "chatter
to itself" (OK for clean input, not so trustworthy for a hysteretic
comparator which may have AC aspects which bend "DC" (as
chatter PWM) Vout. Your CMRR (as an amplifier) is
db20(dVout/dVcm) from wherever you call your "0" reference.
Me, I'd be more interested in the front end error, dVio/dVcm
as the linear CMRR also has to do with the highly variable AVOL,
yet most comparator applications care about Vio and tPD with
AVOL being "lost in the bang-bang".

LaTeX Commands Quick-Menu:

Part and Inventory Search

Welcome to