DIGITALLY CONTROLLED PROGRAMMABLE ATTENUATOR

摘要

A digitally controlled programmable attenuator (10) maintains tight phase matching between attenuated signals over wide ranges of frequencies and power levels regardless of the selected attenuation level. This is achieved with a multi-tap ladder network (12) that sets a desired tap-to-tap dB step-size, a plurality of unity gain digitally switched voltage-to-voltage buffers (14) that are connected between the respective taps (16a, 16b, ... 16n) and a common output (18), and a fixed gain stage (20) that sets the overall gain/attenuation of the attenuator. The buffers (14) maintain a high and substantially constant impedance whether turned on or turned off. Phase matching within 0.2 degree at frequencies up to 300 MHZ for 30 dB of gain variation has been realized. The buffers (14) can be implemented with complementary bipolar or BiCMOS processes.