Termination circuit for an R-2R, ladder that compensates for the

Details Termination circuit for an R-2R, ladder that compensates for the Termination circuit for an R-2R, ladder that compensates for the

1989-11-20

1992-06-02

Fuller, Benjamin R.

Coded data generation or conversion

Analog to or from digital conversion

Digital to analog conversion

341119, 341127, H03M 178

Patent

active

051190940

ABSTRACT:
A termination circuit for an R-2R ladder network for producing weighted currents, the 2R terminating resistor of the ladder being connected to an excitation source voltage which is 2(kT/q)ln 2 closer to the supply voltage than the emitter of the current source in the last (i.e., least significant) leg of the ladder. The excitation source is fabricated with just one type of bipolar transistor and does not require anamplifier or frequency compensation capacitor(s). The excitation source is a simple circuit requiring only five transistors, at least one of which has an emitter area which is a multiple of the emitter areas of the current source transistors. The base-emitter voltages of the transistors in the excitation source are connected in a voltage loop that goes from a voltage V.sub.LSB at the emitter of the current source transistor connected to the least significant ladder network shunt resistor to a voltage, Vt, which would be equal to V.sub.LSB, if all six transistors in the loop had the same emitter area, but which deviates therefrom by 2(kT/q)ln 2 due the differences in the emitter areas.

REFERENCES:
patent: 3893018 (1975-07-01), Marley
patent: 3940760 (1976-02-01), Brokaw
patent: 4176344 (1979-11-01), Saari et al.
patent: 4349811 (1982-09-01), Brokaw
patent: 4591780 (1986-05-01), Yamada et al.
patent: 4882533 (1989-11-01), Kelley
patent: 4899152 (1990-02-01), Barrow et al.
The Engineering Staff of Analog Devices Analog-Digital Conversion Handbook (3rd ed.) pp. 277-294 Prentice-Hall, Eaglewood Cliffs, N.J. .COPYRGT. 1986 by Analog Devices Inc.

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