Browse Prior Art Database

MOSFET Sense Amplifier with Low Input Impedance

IP.com Disclosure Number: IPCOM000076066D
Original Publication Date: 1972-Jan-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 30K

Publishing Venue

IBM

Related People

DeSimone, RR: AUTHOR [+3]

Abstract

When detecting memory sense signals on lines with relatively heavy capacitive loads, it is generally accepted that a low-input impedance current-sensing amplifier is faster than a comparable voltage sensing scheme. Bipolar transistor amplifiers have been used extensively for this purpose in the past, because bipolar devices lend themselves to low-input impedance amplifier designs. Because of the costliness and high-power dissipation of bipolar amplifiers, it is desirable to have a metal-oxide-silicon field-effect transistor, MOSFET, circuit which could be used to sense FET memory signals.

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MOSFET Sense Amplifier with Low Input Impedance

When detecting memory sense signals on lines with relatively heavy capacitive loads, it is generally accepted that a low-input impedance current- sensing amplifier is faster than a comparable voltage sensing scheme. Bipolar transistor amplifiers have been used extensively for this purpose in the past, because bipolar devices lend themselves to low-input impedance amplifier designs. Because of the costliness and high-power dissipation of bipolar amplifiers, it is desirable to have a metal-oxide-silicon field-effect transistor, MOSFET, circuit which could be used to sense FET memory signals.

The figure is a schematic diagram of an amplifier circuit, composed only of FET devices. The circuit consists of two shunt-shunt negative-feedback amplifiers in a differential configuration. Devices J3 and J4 provide primary control of amplifier gain and are the feedback devices, which not only increase the circuit bandwidth but lower the differential input impedance. Load devices J1 and J2 may be operated either in the linear or the pinched-off mode with proper selection of bias voltages V(Drain) and V(Gate), although it has been determined that the former mode results in decreased power dissipation and a narrower dynamic range. The range is still sufficient for small signal applications however. Device J7 with its associated biases (V(Ref) and V(Lo)) approximates a constant- current drain, maintaining active devices J5 and J6 in...