Method and apparatus for common mode control
AssigneeMarvell International Ltd.
InventorThart Fah Voo
Life of this patent
Estimating the term…
Abstract
A common mode feedback circuit is provided that can set a direct voltage operating point of the outputs of an associated amplifier. A feedback path of common mode feedback circuit is configured to be independent from and not pass through the associated amplifier. The common mode feedback circuit can remain powered on during power down of the associated amplifier and maintain a large feedback loop capacitance (in the common mode feedback circuit) at an approximately normal operating voltage to advantageously reduce settling time of an associated amplifier that has been powered off.
Claims67
An amplifier, comprising:
- an input stage configured to receive an input;
- an amplification stage coupled to the input stage, the amplification stage configured to amplify the input and generate a differential amplified output, the differential amplified output having an associated common mode voltage level;
- and
- a common mode feedback circuit coupled to the amplification stage, the common mode feedback circuit configured to control the common mode voltage level through a feedback loop,
- wherein the feedback loop is configured such that the feedback loop is independent from the amplification stage.
A disk drive system, comprising:
- a read/write head configured to sense changes in magnetic flux on a surface of a disk, and generate a corresponding analog signal;
- a preamplifier configured to amplify the analog signal, the preamplifier including,
- an input stage configured to receive the analog signal;
- an amplification stage coupled to the input stage, the amplification stage configured to amplify the analog signal and generate an amplified analog signal, the amplified analog signal having an associated common mode voltage level;
- and
- a common mode feedback circuit coupled to the amplification stage, the common mode feedback circuit configured to control the common mode voltage level through a feedback loop,
- wherein the feedback loop is configured such that the feedback loop is independent from the amplification stage;
- and
- a read channel configured to receive the amplified analog signal and generate a digital read signal based on the amplified analog signal.
A common mode feedback circuit for indirectly controlling a common mode voltage level at an output of an associated amplifier, the common mode feedback circuit comprising:
- a feedback loop including,
- an error amplifier configured to compare a reference voltage to a voltage at a node in the feedback loop and generate a feedback voltage based on the comparison, the error amplifier further configured to send the feedback voltage to a feedback transistor in the feedback loop;
- and
- the feedback transistor configured to receive the feedback voltage and adjust the voltage at the node in the feedback loop,
- wherein the voltage at the node in the feedback loop is independent from an amplifier associated with the common mode feedback circuit.
A method for controlling a common mode voltage level associated with an output of a differential amplifier, the method comprising:
- amplifying an input signal and generating an amplified output signal, the amplified output signal having an associated common mode voltage level;
- generating a common mode feedback voltage through a feedback loop, the common mode feedback voltage controlling the common mode voltage level, the feedback loop being independent from the amplified output signal;
- adjusting the common mode voltage level based on the common mode feedback voltage;
- discontinuing amplification of the input signal;
- and
- continuing to generate the feedback voltage through the feedback loop.
A method for switching a differential amplifier, the differential amplifier having an input and a differential output, the differential amplifier including a feedback circuit to control a common mode voltage of the differential output, the method comprising:
- powering off the differential amplifier;
- decoupling the feedback circuit from the differential amplifier;
- and
- powering on the feedback circuit while the differential amplifier is powered off.
An amplifier, comprising:
- means for receiving an input;
- amplifying means for amplifying the input and generating a differential amplified output, the differential amplified output having an associated common mode voltage level;
- and
- controlling means for controlling the common mode voltage level through a feedback loop means,
- wherein the feedback loop is configured such that the feedback loop means is independent from the amplifying means.
A disk drive system, comprising:
- sensing means for sensing changes in magnetic flux on a surface of a disk, and generating a corresponding analog signal;
- means for amplifying the analog signal, the means for amplifying including,
- means for receiving the analog signal;
- amplifying means for amplifying the analog signal and generating an amplified analog signal, the amplified analog signal having an associated common mode voltage level;
- and
- controlling means for controlling the common mode voltage level through a feedback loop means,
- wherein the feedback loop means is configured such that the feedback loop means is independent from the amplifying means;
- and
- means for receiving the amplified analog signal and generating a digital read signal based on the amplified analog signal.
A common mode feedback circuit for indirectly controlling a common mode voltage level at an output of an associated amplifier, the common mode feedback circuit comprising:
- a feedback loop means including,
- comparing means for comparing a reference voltage to a voltage at a node in the feedback loop means and generating a feedback voltage based on the comparison, the comparing means further configured to send the feedback voltage to adjusting means in the feedback loop means;
- and
- the adjusting means for receiving the feedback voltage and adjusting the voltage at the node in the feedback loop means,
- wherein the voltage at the node in the feedback loop means is independent from an amplifier associated with the common mode feedback circuit.
Dependencies are inferred from the claim text.