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Accurate Biasing of Bipolar Differential Amplifiers with CMOS Feedback Circuitry

IP.com Disclosure Number: IPCOM000116072D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 63K

Publishing Venue

IBM

Related People

Girard, P: AUTHOR [+2]

Abstract

Disclosed is a control circuitry for accurate biasing of differential amplifiers, such as bipolar pairs. The conventional biasing of a differential amplifier may not offer a sufficient regulation performance when the output level has to be known precisely (to be compared to a reference level for example). The novel circuit compares the output signal to the desired voltage level and feedbacks the error information to the biasing control of the amplifier.

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Accurate Biasing of Bipolar Differential Amplifiers with CMOS Feedback
Circuitry

      Disclosed is a control circuitry for accurate biasing of
differential amplifiers, such as bipolar pairs.  The conventional
biasing of a differential amplifier may not offer a sufficient
regulation performance when the output level has to be known
precisely
(to be compared to a reference level for example).  The novel circuit
compares the output signal to the desired voltage level and feedbacks
the error information to the biasing control of the amplifier.

      The principle of the novel circuit is illustrated by reference
to Fig. 1.  The signal amplifier is built around a bipolar
differential pair loaded by two resistors (Rl1 & Rl2), this stage is
biased by Rh, Rl, Rj, Qj & Qh that realize a resistor ratioed current
source.  An output buffer stage increases the driving capability
without degrading the amplifier bandwidth.  The output signal Vo is
the image of the input signal Vi multiplied by the amplifier gain.

      The novel circuit is basically comprised of a common mode
circuit, an error amplifier and a feedback current source.  The
output value to be obtained is set by a voltage reference.  The total
biasing current is given by the sum of Ib and If where If is
controlled by the feedback path.  When the error voltage Ve is
positive (resp.  negative), the feedback current is increased (resp.
decreased) so that the common mode value of the output signal Vo
decre...