Read-head preamplifier having internal offset compensation

A circuit, comprising:

• a differential amplifier having first and second amplifier input terminals and having first and second amplifier output terminals, the amplifier operated to respectively receive first and second components of a differential input signal on the first and second amplifier input terminals and to generate a differential output signal across the amplifier output terminals, the differential output signal having an offset component;
• an offset compensator having first and second input terminals respectively coupled to the first and second amplifier output terminals and having a compensation terminal coupled to the first amplifier input terminal, the compensator operated to maintain the offset component of the differential output signal at a predetermined value by generating an offset-compensation signal on the compensation terminal and superimposing the offset-compensation signal on the respective component of the differential input signal;
• and
• wherein the offset compensator further comprises,
• a third input terminal,
• a supply terminal,
• a high-gain differential amplifier having an output terminal and having first and second input terminals respectively coupled to the first and second input terminals of the offset compensator,
• a transistor coupled between the supply terminal and the compensation terminal, the transistor having a control terminal coupled to the output terminal of the high-gain differential amplifier, and
• a compensation capacitor coupled between the compensation and third input terminals.

An integrated circuit for amplifying a differential read signal from a read head, the circuit comprising:

• first and second circuit input terminals operable to differentially receive the read signal;
• a differential amplifier having a first amplifier input terminal coupled to the first circuit input terminal, a second amplifier input terminal, and first and second amplifier output terminals, the amplifier operable to generate an offset signal and an amplified read signal on the first and second amplifier output terminals;
• and
• a offset compensation circuit having first and second input terminals respectively coupled to the first and second amplifier output terminals, a third input terminal coupled to the second circuit input terminal, a compensation terminal coupled to the second amplifier input terminal, and a single and only a single compensation element, which is coupled between the compensation terminal and the third input terminal, the offset-compensation circuit operable to maintain the offset signal at a predetermined level.

A circuit for amplifying a differential read signal from a read head, the circuit comprising:

• a differential amplifier having first and second amplifier input terminals operable to receive the differential read signal and having first and second amplifier output terminals;
• an offset compensation circuit having first and second input terminals respectively coupled to the first and second amplifier output terminals, a third input terminal, a compensation terminal coupled to the first amplifier input terminal, and a compensation element coupled between the third input terminal and the compensation terminal;
• and
• a driver circuit having first and second driver input terminals respectively coupled to the first and second amplifier output terminals and having first and second driver output terminals.

A read circuit, comprising:

• a read head having first and second read-head output terminals and operable to sense data and to generate a read signal across the output terminals based on the sensed data;
• an amplifier having a first amplifier input terminal coupled to the first read-head output terminal, a second amplifier input terminal, and first and second amplifier output terminals, the amplifier operable to generate an offset signal and an amplified read signal across the amplifier output terminals;
• and
• an offset compensation circuit having first and second input terminals respectively coupled to the first and second amplifier output terminals, a third input terminal coupled to the second read-head output terminal, a compensation terminal coupled to the second amplifier input terminal, and a compensation element coupled to the third input terminal and the compensation terminal, the compensation circuit operable to maintain the offset signal at a predetermined level.

A read circuit, comprising:

• a read head having first and second data terminals;
• an amplifier having first and second amplifier input terminals, the first amplifier input terminal coupled to the first data terminal, the amplifier also having a pair of amplifier output terminals;
• and
• an offset compensation circuit having a pair of input terminals respectively coupled to the amplifier output terminals, a data input terminal coupled to the second data terminal, a compensation terminal coupled to the second amplifier input terminal, and a compensation element coupled between the data input terminal and the compensation terminal.

A disk-drive system, comprising:

• a data-storage disk having a surface;
• a motor coupled to and operable to rotate the disk;
• a read head operable to sense data stored on the disk and to generate a read signal based on the sensed data;
• a read-head positioning assembly operable to move the read head over the surface of the disk;
• and
• a pre-amplifier circuit coupled to the read head, the circuit comprising:
• differential amplifier having a first amplifier input terminal coupled to the read head, a second amplifier input terminal, and first and second amplifier output terminals, the amplifier operable to generate an offset signal and an amplified read signal on the amplifier output terminals;
• and
• an offset compensation circuit having first and second input terminals respectively coupled to the amplifier output terminals, a third input terminal coupled to the read head, a compensation output terminal coupled to the second amplifier input terminal, and a compensation element coupled between the third input terminal and the compensation output terminal, the compensation circuit operable to maintain the offset signal at a predetermined level.

A method, comprising:

• generating a compensation signal based on the level of a steady-state differential output signal from a differential amplifier having first and second input terminals;
• coupling the compensation signal to the second input terminal of the amplifier to maintain the level of the steady-state output signal within a predetermined range;
• coupling a first portion of a read signal to the first input terminal of the amplifier;
• filtering a second portion of the read signal;
• and
• coupling the filtered second portion of the read signal to the second input terminal of the amplifier.

A method, comprising:

• generating a compensation signal based on the levels of first and second low-frequency output signals from a differential amplifier having first and second input terminals;
• coupling the compensation signal to the second input terminal of the amplifier to maintain the level of the first output signal substantially equal to the level of the second output signal;
• receiving a first portion of a differential read signal with the first input terminal of the amplifier;
• filtering a second portion of the differential read signal;
• and
• receiving the second portion of the differential read signal with the second input terminal of the amplifier.

A method, comprising;

• generating a read-head bias signal;
• coupling the bias signal directly to a first input terminal of a differential amplifier;
• coupling the bias signal through a compensation element to a second input terminal of the differential amplifier:
• generating a differential offset signal on output terminals of the differential amplifier in response to the bias signal;
• generating an offset-compensation signal in response to the offset signal;
• and
• superimposing the offset-compensation signal on the bias signal by coupling the offset-compensation signal to the second input terminal of the differential amplifier.

A method, comprising;

• generating a differential read-head bias signal having first and second portions;
• coupling the first portion of the bias signal directly to a first input terminal of a differential amplifier that is disposed on a semiconductor die;
• coupling the second portion of the bias signal to a second input terminal of the differential amplifier through a compensation element disposed on the semiconductor die;
• generating a differential offset signal on output terminals of the differential amplifier in response to the bias signal;
• generating an offset-compensation signal in response to the differential offset signal;
• and
• compensating for the differential offset signal by coupling the offset-compensation signal to the second input terminal of the differential amplifier.