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Decode Driver and Current Source for use in a Monolithic Store

IP.com Disclosure Number: IPCOM000085043D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Battista, M: AUTHOR [+2]

Abstract

The decode driver and constant-current sources depicted in the drawing provides efficient, reliable, switchable constant-current sources. The circuitry may be advantageously employed in a monolithic read-only store.

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Decode Driver and Current Source for use in a Monolithic Store

The decode driver and constant-current sources depicted in the drawing provides efficient, reliable, switchable constant-current sources. The circuitry may be advantageously employed in a monolithic read-only store.

With all inputs at the uplevel, the current through Schottky diodes D1, D2 and D3 is cut off. The base of transistor T1 is at about 3.1 volts (VBE1 + VBE2 + VD5 + VC). VC is the voltage of the clamp circuit formed by resistors R3 and R4 and transistor T3. The voltage VC is relatively constant regardless of variation in the VBE's and beta's of transistors T1 and T2 or the forward drop of Schottky diode D5.

With the base of transistor T1 at 3.1 volts, VC will be approximately 1.0 volt. With VC ~ 1 volt, the constant-current generators (T7, R5; T8, R6; through T22, R20) will conduct. The current supplied by each constant-current generator to memory array lines 1 to 16 is 0.6 ma nominally and varies about +/- 0.1 ma.

When one or all of the inputs to diodes D1 to D3 of the decoder are at the downlevel the base to transistor T1 is at about 1.6 volts. With transistors T1 off, the base of transistors T7, T8, etc. will be near ground. Namely, VC approaches ground potential. As a result, no current will be provided to array lines 1 through 16 by the constant-current generators. Transistors T4, T5, and T6 and Schottky diodes D6 to D21 provide active pull-up to the array lines 1 through 16.

When the d...