Browse Prior Art Database

Low Input Impedance FET (or BI FET) Sense Amplifier

IP.com Disclosure Number: IPCOM000081428D
Original Publication Date: 1974-Jun-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Cassidy, BM: AUTHOR [+2]

Abstract

Described is a low-input impedance sense amplifier circuit which overcomes the disadvantages of capacitance loading and noise implications found in prior art low-impedance sense amplifiers, by adding devices to improve restore, system noise immunity, and to achieve higher speed.

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Low Input Impedance FET (or BI FET) Sense Amplifier

Described is a low-input impedance sense amplifier circuit which overcomes the disadvantages of capacitance loading and noise implications found in prior art low-impedance sense amplifiers, by adding devices to improve restore, system noise immunity, and to achieve higher speed.

Low-impedance sense amplifiers have two major drawbacks. One, the input can be loaded down with a large significant capacitance and since this input must be restored, the devices must be extremely large to achieve reasonable cycle times. Two, it is subject to a few hundred millivolts of noise which can provide erroneous output signals.

The circuit shown in the figure overcomes both of these difficulties in that the input node can now be quickly restored to 95% of its quiescent voltage when T1 is turned off, and the circuit will compensate and avoid any input noise. To restore the input to its quiescent voltage, a restore pulse is applied to the gates of transistors T5 and T4 to turn these devices on, causing the input to be raised to V Ref and the output to be raised to +V. Transistor T7 is held off. Devices T3 and T6 are always on and are selected such that the source of transistor T2 sits at a few hundred millivolts above ground, setting the amount of noise immunity which the input node will have.

During chip access, the restore pulse applied to the gates of transistors T4 and T5 drops and transistor T7 is turned on. This causes the so...