Digitally selectable, multiple current source proportional to a

Details Digitally selectable, multiple current source proportional to a Digitally selectable, multiple current source proportional to a

1986-09-08

1987-10-20

Beha, Jr., William H.

Electricity: power supply or regulation systems

Self-regulating

Using a three or more terminal semiconductive device as the...

340347DA, 340347CC, G05F 322

Patent

active

047016949

ABSTRACT:
A current source utilizes N+1 transistors to produce N output currents of magnitudes proportional to a variable reference current. Each transistor emitter is resistively coupled to a common potential and each transistor base is driven by a common control voltage, offset by a separately adjustable amount for each transistor. The control voltage is produced by an amplifier having a grounded inverting input and a non-inverting input coupled to the collector of a first of the transistors and resistively coupled to a variable reference voltage source. The reference voltage source is adjusted to produce a desired reference current in the collector of the first transistor and the magnitude ratio of an output current produced in the collector of each of the N remaining transistors to the reference current is controlled by adjusting the ratio of emitter resistance of the first transistor to the emitter resistance of the remanining transistors. The control voltager offset for each transistor is adjusted so that the current ratios remain constant over a range of reference current magnitudes despite difference in base-emitter voltage drop between the first and remaining transistors.

REFERENCES:
patent: 3940760 (1976-02-01), Brokan
patent: 4176344 (1979-11-01), Saari et al.
patent: 4349811 (1982-09-01), Brokan
patent: 4458201 (1984-07-01), Keon
Sanford, "Precision Current Source Circuit," IBM Tech. Discl. Bul., vol. 18, No. 9, pp. 2946, 2947, Feb. 1976.

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