CMOS differential amplifier having constant transconductance and slew rate
AssigneeU.S. Philips Corporation
InventorWilliam Redman-White
Life of this patent
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Abstract
An amplifier, particularly a CMOS amplifier has a differential input which is fed to six differential pairs. The outputs of the first and third differential pair are combined and fed to inputs of a summing network, while the outputs of the fourth and fifth are combined and fed to inputs of the summing network. The second and sixth differential pairs are arranged to cancel the tail currents of the fifth and third pairs, respectively, when all of the devices are in their active state. Thus, regardless of the common mode input level with respect to the supply rails the output current is provided by four devices giving a constant g.sub.m and slew rate.
Claims6
A differential amplifier comprising:
- a pair of differential input terminals;
- first, second and third differential pairs of active devices of a first conductivity type having first, second, and third tail currents respectively;
- fourth, fifth and sixth differential pairs of active devices of a second conductivity type having fourth, fifth, and sixth tail currents respectively;
- each of said differential pairs having inputs coupled to said differential input terminals;
- and
- a summing network having inputs coupled to the outputs of the first, third fourth and fifth differential pairs and having an output which constitutes the output of the amplifier;
- wherein the outputs of the second differential pair are connected in common to the tail of the fifth differential pair, the outputs of the sixth differential pair are connected in common to the tail of the third differential pair, the tail current of the second differential pair is equal to that of the fifth differential pair, and the tail current of the third differential pair is equal to that of the sixth differential pair.
Dependencies are inferred from the claim text.