US 4,797,631 A · Folded cascode amplifier with rail-to-rail common-mode range

Abstract

A folded cascode amplifier with rail-to-rail common-mode range utilizes a fully differential input with two sets of input common source amplifier devices to allow rail-to-rail common-mode range. The first set of devices utilizes N-channel transistors (28) and (32) to provide operation in one direction and P-channel transistors (38) and (42) to allow operation in the other direction. Two common gate amplifier output legs are provided for generating a differential voltage between an output node (50) and an output node (48) in a cascode configuration. A feedback circuit is provided for maintaining node (50) at analog ground over the full common-mode range of the input voltage. The feedback circuit utilizes a current source with transistors (88) and (90) and a differentially configured set of transistors (80) and (82) to control a feedback transistor (86). The feedback transistor (86) controls the current in both of the output legs to maintain the node (50) at analog ground by receiving at one of the differential inputs the voltage on the node (50) and comparing it with analog ground on the other differential input.

Claims13

Dependent claims

A folded cascode differential amplifier with rail-to-rail common-node range, comprising:

a positive supply rail;
a negative supply rail;
first common source circuitry for converting a differential input voltage to a first differential current and operable to said positive rail;
second common source circuitry for converting said input voltage to a second differential current and operable with a common-node range to said negative rail;
a plurality of first push-pull cascade devices for receiving on an input one side of each of said first and second differential currents for conversion to a voltage on a first output node;
a plurality of second push-pull cascode devices for receiving on an input one side of each of said first and second differential currents for conversion to a voltage on a second output node;
a first current variable load for varying the current through said first ascode devices to vary the voltage on said first output node;
a second current variable load for varying the current through said second cascode devices to vary the voltage on said second output node;
and
a negative-feedback auxiliary amplifier coupled to said cascode devices and said current variable loads, said auxiliary amplifier operable to maintain said cascode devices in linear operation while permitting variations in load current resulting from rail-to-rail common mode operation.

7 more elements

A folded cascode amplifier with rail-to-rail common-mode range, comprising:

a positive supply rail;
a negative supply rail;
a reference voltage;
first common source circuitry for converting a differential input voltage to a first differential current and operable with a common-mode range to said positive rail;
second common source circuitry for converting said input voltage to a second differential current and operable with a common-mode range to said negative rail;
first push-pull common gate circuitry for receiving on an input one side of each of said first and second differential currents for conversion to a voltage on a first output node;
second push-pull common gate circuitry for receiving on an input one side of each of said first and second differential currents for conversion to a voltage on a second output node;
a first current variable load for varying the current through said first common gate circuitry to vary the voltage on said first output node;
a second current variable load for varying the current in said second common gate circuitry to vary the voltage on said second output node;
control circuitry for controlling said first and second current variable loads to set the common-mode voltage between said first and second output nodes;
and
comparator circuitry for comparing the voltage on said first output node with said reference voltage and controlling said control circuitry to maintain said first output node at said reference voltage in a negative feedback loop.

9 more elements

A folded cascode amplifier with rail-to-rail common-mode range, comprising:

a positive supply rail;
a negative supply rail;
a first common source differential amplifier for converting a differential input voltage to a first differential current and operable with a common-mode range to said positive rail;
a second differential common source amplifier for converting said input voltage to a second differential current and operable with a common-mode range to said negative rail;
a first push-pull common gate circuit for receiving on an input thereof one side of each of said first and second differential currents for conversion to a voltage on a first output node, said first push-pull common gate circuit having a first current variable load that varies in response to an external signal;
a second push-pull common gate circuit for receiving on an input thereof the opposite side of each of said first and second differential currents for conversion to a voltage on a second output node, said second common gate circuit having a second current variable load for varying the current in response to said external signal;
control circuitry for generating said external signal to control the current through said first and second current variable loads to control the common-mode level of the voltage between said first and second output nodes;
and
a comparator for comparing the voltage on said first output node with analog ground and generating an error signal when the voltage on said first output node varies from analog ground, said error signal input to said control circuitry to provide a negative feedback loop such that the common-mode voltage between said first and second output nodes is varied to maintain said first output node voltage proximate to analog ground.

6 more elements

Dependencies are inferred from the claim text.

Folded cascode amplifier with rail-to-rail common-mode range

Life of this patent

Folded cascode amplifier with rail-to-rail common-mode range

Life of this patent

Abstract

Claims13