Communications: electrical – Continuously variable indicating – With meter reading
Patent
1996-11-13
1999-06-08
Horabik, Michael
Communications: electrical
Continuously variable indicating
With meter reading
395311, 395312, 348705, 326113, 361 60, H04Q 1900, G06F 1300, H04N 5268, H03K 19094
Patent
active
059107804
ABSTRACT:
A switched-transconductance circuit used in a multiplexer forming a part of a crosspoint switch includes integrated T-switches that are enabled when the transconductance stage is not enabled. The transconductance stage is selectively enabled by controlling a split-tail current source driving a differential pair of input transistors. When the transconductance stage is disabled (1) a pair of switches connected between the collectors of the differential pair and a positive voltage supply node are enabled, (2) a pair of cascode transistors connected between the collectors of the differential pair and output leads of the circuit are reversed biased by the positive supply voltage passing through the pair of switches, and (3) a switch is enabled between a common emitter node of the differential pair and a low impedance constant voltage node. In this manner, a pair of common collector T-switches and an emitter T-switch are formed, respectively, between the inputs and output and between the differential inputs of the transconductance stage when the transconductance stage is disabled. When the transconductance stage is enabled, the emitter T-switch is disabled and an additional current source, controlled by the same control signal that controls the split-tail current source, drives a current through a resistor to create a voltage that disables the pair of switches. The disabling of the switches disallows the positive voltage from passing therethrough, thereby forward biasing the cascode transistors. In this state, the collector and emitter T-switches are disabled and the circuit functions as an ordinary differential transconductance circuit.
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Analog Devices Inc.
Asongwed Anthony A.
Horabik Michael
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