Browse Prior Art Database

High Speed Polarity Switchable Precision Current Source

IP.com Disclosure Number: IPCOM000082079D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 61K

Publishing Venue

IBM

Related People

Jaeger, RC: AUTHOR

Abstract

A precision current source with high-speed polarity control is provided for bipolar requirements well suited for construction as linear integrated circuits. The polarity switchable current source is obtained using two current sources 11 and 12 of values I and 2I, respectively, as shown in Fig. 1. With switch 10 connected to ground, a load current IL equal to +I flows; with the switch 10 connected to the load, a load current IL equal to -I flows. In this manner, a switchable current source of value + or - is obtained.

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High Speed Polarity Switchable Precision Current Source

A precision current source with high-speed polarity control is provided for bipolar requirements well suited for construction as linear integrated circuits. The polarity switchable current source is obtained using two current sources 11 and 12 of values I and 2I, respectively, as shown in Fig. 1. With switch 10 connected to ground, a load current IL equal to +I flows; with the switch 10 connected to the load, a load current IL equal to -I flows. In this manner, a switchable current source of value + or - is obtained.

In the embodiments shown, current levels can be detected at the current sense terminals CS and switch driving signals are applied at terminals SD. The circuit of Fig. 2 shows one embodiment of the precision matched current sources. Transistor 21 biases matched transistor device 22 and provides a current source to drive the buffered current mirror formed by transistors 23, 24, 25 and 26. The collector currents of transistors 24 and 25 are summed to provide the current source 2I, and the collector current of 22 provides the current source I. Switch 10 is realized using a differential pair as a current switch. Transistor 27 buffers device 28 to minimize the current error caused by the finite beta of transistor 28. Resistors R are precision thin/thick film resistors external to the integrated circuit.

A second embodiment is shown in Fig. 3. Transistor 31 biases like transistor devices 32 and 33 and...