Low-voltage, broadband operational amplifier
AssigneeTexas Instruments Incorporated
InventorKrishnasawamy Nagaraj
Life of this patent
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Abstract
A low voltage, broadband differential operational amplifier which eliminates the long tail current source from the amplifier, thereby relieving the headroom requirements by a few tenths of a volt. An input common mode feedback circuit is used to overcome the problems arising from the removal of the long tail current source of prior art circuits. This circuit monitors the common mode feedback current and when the value of the current exceeds a specified range around the nominal amplifier bias current, an appropriate correction in the common mode input voltage is made. This novel amplifier will be valuable for use in pipelined analog-to-digital converter applications, as well as many other low voltage and/or portable applications.
Claims10
A first method for generating an operational amplifier common mode input correction voltage, comprising:
- generating a common mode feedback signal;
- establishing replicas of the amplifier common mode currents;
- generating UP and DOWN counter control signals by comparing replica common mode currents to upper and lower current limits;
- and
- providing a corrected input common mode voltage using an UP/DOWN counter, a digital-to-analog converter, and summing circuit to develop a small correction current which is summed to the nominal amplifier bias current.
A first apparatus for generating an operational amplifier common mode input correction voltage, comprising:
- generating a common mode feedback signal;
- establishing replicas of the amplifier common mode currents;
- generating UP and DOWN counter control signals by comparing replica common mode currents to upper and lower current limits;
- and
- providing a corrected input common mode voltage using an UP/DOWN counter, a digital-to-analog converter, and summing circuit to develop a small correction current which is summed to the nominal amplifier bias current.
A second method for generating an operational amplifier common mode input correction voltage, comprising:
- replicating the current flowing in the input transistors of the main operational amplifier and generates UP and DOWN counter control signals by comparing replica currents to the upper and lower current limits;
- providing a corrected input common mode voltage using an UP/DOWN counter, a digital-to-analog converter, and summing circuitry to develop a small correction current which is summed to the nominal amplifier bias current.
A second apparatus for generating an operational amplifier common mode input correction voltage, comprising:
- replicating the current flowing in the input transistors of the main operational amplifier and generates UP and DOWN counter control signals by comparing replica currents to the upper and lower current limits;
- providing a corrected input common mode voltage using an UP/DOWN counter, a digital-to-analog converter, and summing circuitry to develop a small correction current which is summed to the nominal amplifier bias current.
Dependencies are inferred from the claim text.