Buffer circuit having variable output impedance

Details Buffer circuit having variable output impedance Buffer circuit having variable output impedance

1995-09-05

1997-02-25

Wambach, Margaret Rose

Miscellaneous active electrical nonlinear devices, circuits, and

Signal converting, shaping, or generating

Current driver

327391, H03K 19084

Patent

active

056062753

ABSTRACT:
An output buffer circuit (20) has an output impedance that is adjustable. An external resistor (32) having a resistance that is a multiple of the desired output impedance is coupled to the output buffer circuit (20). A voltage across the resistor (32) is converted to a digital code using an analog-to-digital (A/D) converter (22). A digital code from the A/D converter (24) is used to adjust a resistance of a binary weighed transistor array (45) to match the resistance of the external resistor (32). A plurality of binary weighted output transistors (153, 154, 155) are selected in response to the digital code to adjust the output impedance to match the characteristic impedance of a load driven by the output buffer circuit (20). The output impedance is easily adjustable by changing the resistance of external resistor (32), allowing the output buffer circuit to drive various load impedances.

REFERENCES:
patent: 4490634 (1984-12-01), Hareyano
patent: 5055847 (1991-10-01), Rybicki et al.
patent: 5134311 (1992-07-01), Biber et al.
patent: 5379230 (1995-01-01), Morikawa et al.

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