Common-mode feedback circuit
OwnerJames R. Hochschildinventor
Life of this patent
Estimating the term…
Abstract
The opamp has a common mode current injection circuit that monitors the amount of tail current “requested” by the primary common-mode feedback circuit. If this current exceeds the nominal tail current by a certain amount, additional common-mode current is injected into the first stage of the opamp, bypassing the tail source and the input differential pair, to prevent the outputs from latching. This circuit is useful for an opamp in which the common mode feedback (CMFB) loop controls the tail current. When the “requested” tail current exceeds a threshold, additional current is pumped into the first stage to stabilize the CMFB loop.
Claims18
A circuit comprising:
- a differential input pair;
- a tail current source coupled to the differential input pair;
- a common mode feedback circuit having an output coupled to a control node of the tail current source;
- a current injection circuit for monitoring the output of the common mode feedback circuit and injecting current into nodes coupled to the differential input pair in response to the output of the common mode feedback circuit.
A 2-stage opamp circuit comprising:
- a differential input stage;
- a differential output stage coupled to the differential input stage;
- a tail current source for supplying current to the differential input stage;
- a common mode feedback circuit having inputs coupled to the differential output stage and having an output that controls the tail current source;
- and
- a current injection circuit having an input coupled to the common mode feedback circuit and having outputs coupled to the differential input stage for supplying current to the differential input stage in response to the output of the common mode feedback circuit.
A method comprising:
- monitoring a common mode feedback signal;
- comparing a common mode feedback signal to a reference current;
- providing current to the first stage in response to the common mode feedback signal.
An amplifier circuit comprising:
- an input stage having a tail current source;
- a common-mode feedback circuit for controlling the tail current source;
- a current injection circuit for monitoring an output of the common mode feedback circuit and injecting current into the input stage when the output of the common mode feedback circuit exceeds a threshold.
Dependencies are inferred from the claim text.