Browse Prior Art Database

"More On" Circuit

IP.com Disclosure Number: IPCOM000084963D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Norton, DE: AUTHOR

Abstract

Transistors T1, T2, T1' and T2' as well as T1'' are lateral PNP transistors and operate as current sources only. Transistors T3 and T3' are current sources that provide off drive to transistors T4 and T4', respectively. Transistors T4 and T4' are the only switching transistors in the circuit. All diodes are assumed to be Schottky diodes for the discussion.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 53% of the total text.

Page 1 of 3

"More On" Circuit

Transistors T1, T2, T1' and T2' as well as T1'' are lateral PNP transistors and operate as current sources only. Transistors T3 and T3' are current sources that provide off drive to transistors T4 and T4', respectively. Transistors T4 and T4' are the only switching transistors in the circuit. All diodes are assumed to be Schottky diodes for the discussion.

In operation, diodes D7, D8 and D9 provide a diode AND function on the "front" of the circuit. With any one of the inputs at a downlevel (about 0.3 volt), the current from the collector of transistor T1 is steered from diode D1 through the input diode or diodes that are down. With no current available through diode D1 to keep transistor T4 on, the collector current of T3 tends to turn T4 to its off state. This causes the collector voltage of T4 to rise until it reaches a potential high enough to forward bias diode D2. This potential is the V(be) of T4 plus the forward drop of diode D2 (approximately 1.3 volts).

The collector voltage of T4 balances at this point, with the collector current of T2 supplying the off bias of T4 (collector current of T3) plus enough base current to T4 for T4 collector's current to supply the remainder of the current from transistor T2. (Note: The base of T4 remains forward biased at about 0.75 volt).

The other state of the circuit is assumed when all the inputs are at their uplevel. Then the collector current of T1 is steered through diode D1. This current supplies the off drive provided by T3 and enough base current to T4, so that T4's collector current can exceed that of T2. This results in the potential on the collector of T4 to drop until diode D3 forward biases (about 0.3 volt). Diode D3 then conducts any excess drive current to the base of transistor T4 through T4's collector. In so far as the forward drop of diode D3 is less than the base collector diode of T4, it prevents T4 from storing excess charge. This prevents a long storage delay that would otherwise result. The additi...