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Current Switch Receiver Circuit with Improved AC Noise Tolerance

IP.com Disclosure Number: IPCOM000052529D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Culican, EF: AUTHOR [+2]

Abstract

For circuit concepts with tight threshold band definition rules, receiv circuits of the current switch type are required. The proposed circuit modification provides an improved suppression of AC noise response. An increased AC noise response is normally encountered as a problem in current-switch-type circuits.

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Current Switch Receiver Circuit with Improved AC Noise Tolerance

For circuit concepts with tight threshold band definition rules, receiv circuits of the current switch type are required. The proposed circuit modification provides an improved suppression of AC noise response. An increased AC noise response is normally encountered as a problem in current-switch-type circuits.

Fig. 1 shows the modified current switch receiver with improved AC noise tolerance. Fig. 2 illustrates, for comparison purposes, a conventional approach for that circuit type. The switching transistors preferably are provided with standard SBD (Schottky barrier diode) clamps (not shown).

Considering the two circuits, the DC noise tolerance is approximately the same. The response to AC noise is modified by the addition of T4, RS and R6. Considering now AC noise only: In the up level, noise response is set to a large extent by the discharge of the base of T3. In the circuit of Fig. 2 this is accomplished by the relatively low impedance of T2, R2. In the circuit of Fig. 1, that impedance starts to switch T4, leaving the high impedance R6 to discharge T3. Down level AC noise is suppressed in a similar manner. In Fig. 2, R3 must move from the clamped level to approximately 750 mV to start noise response. In Fig. 1, the movement is to approximately 1 V. This is also coupled with the device characteristics of T4 and the current required by R6 to reduce noise response.

Fig. 3 shows, for comparison, bo...