Browse Prior Art Database

Active Current-Sourced Half-Current Switch

IP.com Disclosure Number: IPCOM000039071D
Original Publication Date: 1987-Apr-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 52K

Publishing Venue

IBM

Related People

Dorler, JA: AUTHOR [+2]

Abstract

Since the introduction of the HCS (half-current switch) logic circuit [1], various enhancements in its performance have been suggested by employing different means of clamping the HCS logic levels. Despite significant improvements in performance realized by such means, the problem of supplying current to the transistors performing the logic (Image Omitted) function in the HCS circuit without the use of a resistor tolerance- dependent linear current source continues. This article discloses a compensated HCS logic circuit (Fig. 2) with a switchable active current source which overcomes these limitations. Fig.

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Active Current-Sourced Half-Current Switch

Since the introduction of the HCS (half-current switch) logic circuit [1], various enhancements in its performance have been suggested by employing different means of clamping the HCS logic levels. Despite significant improvements in performance realized by such means, the problem of supplying current to the transistors performing the logic

(Image Omitted)

function in the HCS circuit without the use of a resistor tolerance- dependent linear current source continues. This article discloses a compensated HCS logic circuit (Fig. 2) with a switchable active current source which overcomes these limitations. Fig. 1 shows a clamped HCS circuit [2] in which the current supplied to transistors T1, T2 and T3 is provided via a linear current source dependent on the resistor tolerance of R3, and is therefore sensitive to process, temperature and power supply changes. These changes are found to result in N 30% overall operation variation. Addition of the inverse, switchable current source shown in Fig. 2

(Image Omitted)

overcomes this problem. By use of an inversely operated transistor 4 which is allowed to saturate, the current source impedance is greatly lowered. As shown in Fig. 3, the improved current source allows a tenfold I while requiring only a 60 mV change in voltage. The lower voltage swing thereby required allows a 100 mV greater noise tolerance at less power. Fig. 4 compares the transfer curve for the original clamped HC...