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Output Logic Level Control of Flip-Flop Integrated Circuits

IP.com Disclosure Number: IPCOM000037894D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-30
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Schrader, RE: AUTHOR [+2]

Abstract

When a power supply voltage is applied, flip flop (F/F) type circuits in differential cascode current switch logic can have undefined output logic levels.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 73% of the total text.

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Output Logic Level Control of Flip-Flop Integrated Circuits

When a power supply voltage is applied, flip flop (F/F) type circuits in differential cascode current switch logic can have undefined output logic levels.

To condition the output voltage of F/F type circuits to both logic levels for testing, a novel method is provided for setting an output in the down level, while using conventional F/F circuitry. An F/F circuit conventionally interconnects two data latch circuits. The FIGURE depicts a data latch connected as the output half of a typical F/F circuit. Outputs 01 and 01N drive additional logic.

Heretofore, transistor Q1 set output 01 in the down level for testing by applying a voltage on the base of Q1 (TESTP) higher than the up level clock voltage.

In the present technique, however, the voltage on TESTP is set about 0.9 volts higher than supply +V. Voltage 0.9 is a transistor VBE plus 100 mV. This forward biases the base-emitter and base-collector junctions of transistor Q1. Current I1 flows from the voltage supply driving TESTP, through the base-emitter junction of Q1 and into the current source. Current also flows from the TESTP supply, through the base-collector junction of Q1, through resistor R1 and into supply +V. The current through resistor R1 sets the voltage on output 01 to about 100 mV above supply +V. No current flows through resistor R2, so the voltage on output 01N is equal to +V. These conditions set output 01N in the down level or 100 mV b...