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Integrated Bicmos Amplifier Coupling Scheme

IP.com Disclosure Number: IPCOM000035346D
Original Publication Date: 1989-Jul-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Buchholtz, TC: AUTHOR [+3]

Abstract

This method allows AC coupling without sacrificing any transient response performance, and is used in the read data path of a direct access disk drive.

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Integrated Bicmos Amplifier Coupling Scheme

This method allows AC coupling without sacrificing any transient response performance, and is used in the read data path of a direct access disk drive.

The majority of the data channel was resident on an ACMOS module capable of being powered from up to a 5-volt supply. The ACMOS module was required to amplify and filter the disk read signal coming from a head pre-amp powered from a 12-volt supply. The pre-amp signal output voltage was a few millivolts peak-to-peak on top of a few hundred DC millivolt offset. The ACMOS module had to AGC the AC signal up to 1 vp-p and active-filter it. The active filter contained a number of amplifiers interconnected by filter sections. The filters were both single-ended and differential and introduced a significant DC component to the AC signal. The large AC signal amplitude that was needed, compared to the small power supply voltage (this function was previously done with a 12-volt supply), dictated some form of AC coupling to remove the variable DC offset, level translate, and recover the center of a single-ended AC waveform.

The figure shows a schematic of the front end section of the AGC in the ACMOS module. The AC coupling capacitors are placed in series with the FBO and FDO differential inputs. The resistors that form the other end of the high pass filter are R1 and R2. FVO is a chip reference voltage that the resistors DC center to. This voltage can be whatever the optimum level o...