International Business Machines Corporation

Chorng K Wang

Paul Wingshing Chung

David A Freitas

Paik Saber

David S Lowrie

Roomy Khan

A fully differential operational amplifier having unity gain is provided. The amplifier includes a differential input stage having two pairs of differential inputs. One pair receives the input signal. The other pair is connected internally to receive differential mode feedback from the output stage. The two pairs of differential inputs are combined with a common mode feedback signal and cascoded to the output. The amplifier incorporates automatic internal noise cancellation due to its differential mode feedback, and may be constructed in MOS logic, or in BiCMOS for high frequency operation. Applications include buffering for filters in circuitry requiring high speed and noise cancellation, such as data channels and servo channels in data recording devices.

Fully differential follower using operational amplifier

A digital-to-analog converter for use in a timing control loop. The converter includes a plurality of cells, each activated in response to a timing loop control signal. The converter also includes a resistive current mirror, with a first resistance R1, providing a reference curent which is mirrored in each cell by a current source FET. Each cell is constructed to switch the current from its current source FET through an output FET when a respective control bit provided to the cell is positive. Otherwise, the current is diverted through a sink FET. All of the cell output FETs are tied to a single resistance R2 which collects the currents of the active cells and provides the AC output of the converter. The converter's output is related only to the ratio R2/R1, thereby decoupling process, temperature, and voltage effects from the output of the converter.

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San Jose, CA, United States of America

Chorng K Wang