Bell Telephone Laboratories

At&t Bell Labs

Herbert Anton Schneider

The subject array structure provides a large current mirror array which generates a plurality of substantially equal output currents from high impedance sources in response to at least one input control current. This array structure reduces the control current deviation problem of prior art current mirror circuits.

Precision current mirror arrays

Improved current sources which provide n output units of current responsive to m input units of current are constructed by connecting (m+n).sup.2 transistors in a square array configuration, controlled by (m+n) control devices. The array contains (m+n) columns each of which conducts a current the magnitude of which is desired to equal the magnitude of the current flowing in every other column, and has a maximum deviation only in proportion to [1/(1+.beta.)].sup.4 where .beta. is the common emitter current gain of the transistors.

Current mirror arrays

A semiconductor switching network is disclosed in which complementary bipolar transistors are employed as 'floating' crosspoints. Each crosspoint consists of a pair of complementary bipolar transistors with each transistor being connected in series with one of the leads of the communication pair. Each one of the complementary bipolar transistors is, in turn, surrounded by a 'protective control shell' of diodes and transistors which provides the crosspoint with overvoltage and reverse voltage protection and secures crosspoint turn-off. Additionally, the protective control shell contains a self-bias arrangement to eliminate the need for external power supplies to operate the crosspoint as well as an optoisolator control circuit to eliminate direct connections to external control circuits. Thus, the disclosed 'protective control shell' converts the complementary bipolar transistors into a 'floating' crosspoint - powered solely from the communication leads with no direct connection to any external power supply or control circuit, which crosspoint is insensitive to both the polarity and the magnitude of the applied voltage and current.

Bipolar transistor switching network crosspoint

Signal transmission circuit characteristics are supplemented by a negative conductance circuit in which current sources of complementary polarity are connected in shunt between the conductors of the signal circuit. Changes in the voltage level of one side of the signal circuit are sensed at a point common to the two sources and applied through a positive impedance to control the current output magnitude of one of the sources for effecting a supplementing of the signal circuit current as though the changed voltage level had been applied in the presence of a negative form of that impedance connected at that common point. In additional embodiments, different, or variable, positive impedance are connected in the sensing circuit output coupling to cause the negative of such impedance to appear at such signal circuit terminal.

Negative conductance network

Improved current mirrors are provided by connecting current mirrors of known types in cascode.

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Boulder, CO, United States of America

Herbert Anton Schneider