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Current Switch With Emitter Compensating Network

IP.com Disclosure Number: IPCOM000093250D
Original Publication Date: 1967-Jul-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 3 page(s) / 43K

Publishing Venue

IBM

Related People

Axelrod, MS: AUTHOR

Abstract

Current stability in high-speed, integrated, current-switching circuits is achieved without degradation of speed performance. This is effected by making the emitter compensating networks a specified function of frequency omega, i.e., a high impedance at lower frequencies and a low impedance at higher frequencies. The emitter compensating networks utilize either a small physical capacitor or a transistor or both having a large base transit time tau to accomplish this required frequency dependence and minimize space requirements.

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Current Switch With Emitter Compensating Network

Current stability in high-speed, integrated, current-switching circuits is achieved without degradation of speed performance. This is effected by making the emitter compensating networks a specified function of frequency omega, i.e., a high impedance at lower frequencies and a low impedance at higher frequencies. The emitter compensating networks utilize either a small physical capacitor or a transistor or both having a large base transit time tau to accomplish this required frequency dependence and minimize space requirements.

In A, a current-switching network for performing a Nor logical function comprises a plurality of input transistors T1...TN. The latter have collectors commoned at point X and emitters commoned at point Y. Input terminals 1 are connected at each base electrode. Point X is connected along load resistor R1 to voltage source V1 and, also, to the base of output transistor T2. The latter is arranged as an emitter-follower. The collector is connected to source V1. The emitter is connected at output terminal 0 and along resistor R2 to -V3. Point Y is connected to the emitter of transistor T3, base and collector electrodes being commoned and connected to voltage source V2.

When each input terminal I is unenergized, the voltage at point Y is such that T3 is conducting and T1...TN are nonconducting. When an input terminal 1 is energized and the corresponding one of T1...TN is driven into conduction, the voltage at point Y is increased. This occurs sufficiently to render T3 nonconducting. The voltage at point X is reduced sufficiently to render T2 conducting so that an output signal is developed at output terminal 0.

Compensating network CN stabilizes emitter current Ie of T1...TN and T3 at point Y. Network CN includes transistor T4. The collector is connected at point
Y. The emitter is connected along current limiting resistor R3 to bias source -V3. The base is connected to ground along bias resistor R4. Feedback capacitor Cf is connected between collector and base electrodes of T4. Network CN presents a larger effective capacitance than that presented by Cf because of the amplifying effect of T4. At low frequencies, the input impedance of network CN is given by Z=>R3-j(1/omega CfR/R3)| in parallel with >R4-j(1/omega Cf)| where R=R4/ >1+(R4/beta R3)| for R3>>r' and beta R3>>r'' where r' and r'' are the emitter and base resistances, respectively, of T4. The effect of capacitor Cf, therefore, is multiplied by a...