Large common mode input range CMOS amplifier
First Claim
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1. An amplifier comprising:
- a differential pair of NMOS transistors;
an NMOS transistor connected to said NMOS differential pair to conduct the tail current thereof;
a differential pair of PMOS transistors;
a PMOS transistor connected to said PMOS differential pair to conduct the tail current thereof;
means connecting said NMOS differential pair together with said tail current NMOS transistor between two supply rails;
means connecting said PMOS differential pair together with said tail current PMOS transistor between said supply rails;
first and second input terminals to provide an input signal to said NMOS and PMOS differential pairs;
means responsive to the input signal for controlling said tail-current NMOS and PMOS transistors to effect adaptive biasing of said transistors; and
means to combine the outputs of said differential pairs to produce a composite output signal.
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Abstract
A CMOS amplifier input stage including an NMOS differential pair connected in parallel with a PMOS differential pair. Each pair is connected to a tail-current transistor of the same type, and the combined circuits are coupled between positive and negative supply rails. The gates of the tail-current transistors receive the amplifier input signal to provide adaptive biasing of the differential pairs, resulting in a total combined transconductance for both differential pairs which is at least approximately constant with changes in input signal level, thereby enlarging the available common-mode input signal range of the amplifier.
32 Citations
11 Claims
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1. An amplifier comprising:
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a differential pair of NMOS transistors; an NMOS transistor connected to said NMOS differential pair to conduct the tail current thereof; a differential pair of PMOS transistors; a PMOS transistor connected to said PMOS differential pair to conduct the tail current thereof; means connecting said NMOS differential pair together with said tail current NMOS transistor between two supply rails; means connecting said PMOS differential pair together with said tail current PMOS transistor between said supply rails; first and second input terminals to provide an input signal to said NMOS and PMOS differential pairs; means responsive to the input signal for controlling said tail-current NMOS and PMOS transistors to effect adaptive biasing of said transistors; and means to combine the outputs of said differential pairs to produce a composite output signal. - View Dependent Claims (2, 3, 4, 5)
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6. In a CMOS amplifier having NMOS and PMOS differential pairs connected in parallel;
the method of extending the amplifier operating range comprising; controlling the tail currents of both of said differential pairs in accordance with the square of variations in the input signal to said differential pairs; and combining the outputs of said differential pairs. - View Dependent Claims (7)
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8. In a CMOS amplifier having NMOS and PMOS differential pairs connected in parallel between supply rails, the method of extending the amplifier input signal range comprising:
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control means for controlling the tail currents of both of said differential pairs in a way to maintain an effectively constant transconductance of both differential pairs; said control means comprising series variable impedance means through which said tail current flows; said variable impedance means including a control electrode for varying the magnitude of impedance in accordance with the magnitude of voltage of said control electrode; means for applying to said control electrode a control signal directly corresponding to the amplifier input signal; and combining the outputs of both differential pairs to form a composite output signal. - View Dependent Claims (10, 11)
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9. In a CMOS amplifier having NMOS and PMOS differential pairs connected in parallel between supply rails, the method of extending the amplifier input signal range comprising:
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controlling the tail currents of said differential pairs in a way to maintain an effectively constant transconductance of both differential pairs by controling the tail currents so that they are made proportional to the square of the input signal level; and combining the outputs of both differential pairs to form a composite output signal.
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Specification