Large common mode input range CMOS amplifier
AssigneeAnalog Devices, Inc.
InventorPaul A. Spitalny
Life of this patent
Estimating the term…
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.
Claims11
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.
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.
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:
- 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.
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:
- 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.
Dependencies are inferred from the claim text.