Browse Prior Art Database

DISCRETE GAIN CONTROLLED AMPLIFIER

IP.com Disclosure Number: IPCOM000005920D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2001-Nov-15
Document File: 1 page(s) / 60K

Publishing Venue

Motorola

Related People

Stuart G. Langley: AUTHOR

Abstract

Digital gain control of amplifier circuits is required in the design of many linear circuits. This can be achieved by digitally selecting various feedback resistors, usually employing a DAC, to modify the gain of an op amp circuit. Such a design is limited to low power output, which must be amplified by additional analog circuitry, requires multiple supply voltages, and expensive components.

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MO7VROLA Technical Developments Volume 10 March 1990

DISCRETE GAIN CONTROLLED AMPLIFIER

by Stuart G. Langley

   Digital gain control of amplifier circuits is required in the design of many linear circuits. This can be achieved by digitally selecting various feedback resistors, usually employing a DAC, to modify the gain of an op amp circuit. Such a design is limited to low power output, which must be amplified by additional analog circuitry, requires multiple supply voltages, and expensive components.

   A new MOS device is illustrated in FIGS. 1-2 which integrates DAC conversion into a standard vertical DMOS or IGBT structure. The device will accept binary input of n-bits and produce an output current which is essentially propor- tional to the digital input word. The new element in the device is a "split gate". Although only two sections are shown in FIG. 1, any number of gates can be formed on a single device, each gate controlling a predetermined channel width, or number of cells. The output current and gain of an MOS device in saturation is quite constant with applied voltage, and is a function of total channel width. Aside from the polysilicon gate photoresist process, all other processing is iden- tical to standard DMOS or IGBT processing, producing a series of parallel MOSFETs with common source and drain terminals. (see FIG. 2) The output current of each section is binary weighted, (i.e. 2, 4, 6, 16. .) By turning on a new section of the device, the user ef...