Amplifier with input referred common-mode adjustment
AssigneeMotorola, Inc.
InventorsDaniel D. Alexander, David J. Anderson
Life of this patent
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Abstract
A circuit and method control the common-mode potential at an output (17, 18) of a fully differential amplifier (32) by feeding forward a common-mode correction signal through the amplifier. An input signal (V.sub.IN+ -V.sub.IN-) is amplified in the amplifier to produce a differential output signal (V.sub.O- -V.sub.O+) at the output. A common potential of the differential inputs (37, 38) of the amplifier is sensed with a transistor (54, 56) biased to a reference voltage (V.sub.CM) and amplified through the amplifier to produce a common-mode correction signal to offset a common-mode component of the differential output signal. A feedback circuit (33-36) is used to develop the common potential from the common-mode component.
Claims23
An amplifier, comprising:
- a differential signal path having a common node coupled for receiving a tail current and first and second outputs to produce an output signal in response to first and second input signals;
- a compensation circuit coupled between the common node and the first output and having a control input coupled for receiving a reference voltage, wherein the compensation circuit produces a common-mode compensation signal at the first output as a function of the reference voltage and a common potential of the first and second input signals;
- and
- a passive element coupled between the first output and a first input of the differential signal path to develop a common-mode component of the output signal as the common potential of the first input signal.
A method of amplifying, comprising the steps of:
- supplying a tail current to a common node;
- steering a differential current from the common node to first and second outputs to produce a differential output signal in response to a differential input signal;
- applying a reference voltage to steer a compensation current from the common node to the first output;
- and
- comparing the reference voltage to a common potential of the differential input signal to produce the compensation current.
An amplifier, comprising:
- a first transistor having a control electrode coupled to a first input of the amplifier for receiving a first differential input signal, a first conduction electrode coupled to a first common node for receiving a first tail current, and a second conduction electrode coupled to a power supply conductor;
- a second transistor having a control electrode coupled for receiving a reference signal, a first conduction electrode coupled to the first common node, and a second conduction electrode coupled to a first node for providing a first differential output signal;
- a third transistor having a control electrode coupled for receiving the reference signal, a first conduction electrode coupled to a second common node for receiving a second tail current, and a second conduction electrode coupled to a second node for providing a second differential output signal;
- and
- a fourth transistor having a control electrode coupled to a second input of the amplifier for receiving a second differential input signal, a first conduction electrode coupled to the second common node, and a second conduction electrode coupled to the power supply conductor.
An integrated circuit, comprising a programmable analog array that includes a plurality of programmable analog cells interconnected by a programmable switching network, where a first programmable analog cell of the plurality of programmable analog cells includes an amplifier, comprising:
- a differential signal path having a common node coupled for receiving a tail current and first and second outputs coupled to the programmable switching network to produce an output signal in response to first and second input signals;
- and
- a compensation circuit coupled between the common node and the first output, and having a control input coupled for receiving a reference voltage.
An amplifier, comprising:
- a first transistor having a control electrode coupled for receiving a reference voltage, a first conduction electrode coupled to a first common node of the amplifier for receiving a first tail current, and a second conduction electrode coupled to a first output of the amplifier;
- and
- a second transistor having a control electrode coupled for receiving the reference voltage, a first conduction electrode coupled to a second common node of the amplifier for receiving a second tail current, and a second conduction electrode coupled to a second output of the amplifier;
- a third transistor having a control electrode coupled to a first input of the amplifier for receiving a first input signal, a first conduction electrode coupled to the first common node, and a second conduction electrode coupled to a power supply conductor;
- and
- a fourth transistor having a control electrode coupled to a second input of the amplifier for receiving a second input signal, a first conduction electrode coupled to the first common node, and a second conduction electrode coupled to the first output of the amplifier.
Dependencies are inferred from the claim text.