Re: [SI-LIST] : queries : Differential Amplifier Designing

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From: D. C. Sessions (dcs@lumbercartel.com)
Date: Fri Mar 09 2001 - 07:22:36 PST


On Monday 05 March 2001 03:03, you wrote:
# Hi All,
#
# I have few queries regarding
#
# Differential Amplifier Designing
# --------------------------------
#
# 1. How do we decide which type of differential amplifier (PMOS diff.
# ammp. or NMOS diff. amp.) is used for a particular Vref.

In general, NMOS amplifiers have better speed, but poorer common-mode
rejection due to details of CMOS processing. PMOS amplifiers work best
close to the negative supply, NMOS work better near the positive supply.

# 2. What is the significance of common mode range (the range in which
# differential amplifier operates linearly ie. when transistors are in
# saturation region). Is this range is required while designing a
# differential amplifier. Does the selecion of differential amp.(PMOS or
# NMOS) depends on it.

Common-mode rejection is fairly important since changes in CM potential
couple into the receiver timing to produce jitter. Driver asymmetries,
ground noise, and mode conversion all introduce common-mode noise.

-- 
| I'm old enough that I don't have to pretend to be grown up.|
+----------- D. C. Sessions <dcs@lumbercartel.com> ----------+

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