US 10,205,423 B1Granted

Rail-to-rail source follower

AssigneeNXP USA, Inc.

InventorsPedro B. Zanetta, Ricardo P. Coimbra

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Abstract

A source follower method, system, and apparatus provide rail-to-rail capability to an output voltage terminal of a voltage follower feedback biased CMOS output circuit by providing a control circuit which includes first and second bypass transistors that are connected in parallel between first and second control circuit input/output terminals and controlled, respectively, by first and second control circuit inputs, and which also includes first and second current sources for injecting source and sink currents in the output node as a function, respectively, of a first bypass current through the first bypass transistor which turns ON when the output voltage rises above a top threshold voltage level and of a second bypass current through the second bypass transistor which turns ON when the output voltage falls below a bottom threshold voltage level.

Claims20

Dependent claims

A source follower circuit, comprising:

a voltage follower feedback biased CMOS output circuit connected between first and second supply rail voltages VDD, VSS to generate an output voltage at an output node in response to one or more input voltages or input currents;
and
a control circuit connected to the output node for automatically configuring the voltage follower feedback biased CMOS output circuit into an N-type, PN-type, or P-Type follower stage as a function of the output voltage, the control circuit comprising:
first and second bypass transistors connected in parallel between first and second control circuit input/output terminals and controlled, respectively, by first and second control circuit inputs;
and
first and second current generators for injecting source and sink currents in the output node as a function, respectively, of a first bypass current through the first bypass transistor which turns ON when the output voltage rises above a top threshold voltage level and of a second bypass current through the second bypass transistor which turns ON when the output voltage falls below a bottom threshold voltage level.

3 more elements

An electronic device, comprising:

a rail-to-rail source follower circuit comprising a control circuit configured to receive first and second control circuit inputs and to generate an output voltage and output current at an output node between a source terminal of an N-type Metal-Oxide-Semiconductor (NMOS) transistor and a source terminal of a P-type Metal-Oxide-Semiconductor (PMOS) transistor, wherein the first and second control circuit inputs are configured to drive, respectively, first and second bypass transistors connected in parallel between a gate terminal of the NMOS transistor and a gate terminal of the PMOS transistor, wherein the control circuit provides the output current as a sink current that is proportional to a drain current of the second bypass transistor and provides the output current as a source current that is proportional to a drain current of the first bypass transistor, and wherein the first bypass transistor turns ON when the output voltage rises above a top threshold voltage level and wherein the second bypass transistor turns ON when the output voltage falls below a bottom threshold voltage level.

Dependencies are inferred from the claim text.

Facts

Application: 15/675,308Filed 11 Aug 2017
Published: US 2019/0052228 A114 Feb 2019
Granted: 12 Feb 2019
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

H03F 1/0205
Modifications of amplifiers to raise the efficiency, e.g. gliding Class A stages, use of an auxiliary oscillation: in transistor amplifiers
H03F 1/0261
In transistor amplifiers: with control of the polarisation voltage or current, e.g. gliding Class A
H03F 3/21
Power amplifiers, e.g. Class B amplifiers, Class C amplifiers: with semiconductor devices only
H03F 3/3016
CMOS common drain output SEPP amplifiers: with symmetrical driving of the end stage