Pin diode linear attenuator controlled by a companding DAC

Claim 1

A digitally controlled linear radio frequency attenuator, comprising: a companding digital to analog converter having a digital input and an approximated exponential analog current sink output; a current inverter having an input effectively coupled to said exponential analog current sink output, and having an output which provides an output control current which is the inverse of the current appearing at the inverter input; and a PIN diode having a radio frequency input, a linearly attenuated radio frequency output, a control current input and a logarithmic radio frequency attenuation characteristic for use as a radio frequency attenuator, effectively coupled to said current inverter output; whereby a digital input signal to the companding digital to analog converter provides an approximated exponential current sink output which is inverted by the current inverter and provided to the PIN diode to control the logarithmic radio frequency attenuation characteristic to thereby linearly attenuate a radio frequency signal applied to the radio frequency input in response to the digital input to the companding digital to analog converter.