Patent ID: 7205817
Filing Date: 2007-04-17
Classification: H03H

Abstract:
1. A variable attenuator for controllably attenuating an AC signal comprising: a plurality of alternate series and shunt variable resistors coupled between a variable attenuator input and a variable attenuator output, each variable resistor having at least one field effect transistor (FET) having a body, a source, a drain and a gate, with parasitic capacitances between the gate and source, the gate and drain, the source and body and the drain and body, the parasitic capacitances providing respective parasitic impedances at the frequencies of the AC signal; the body of each FET being coupled to a circuit reference through a respective resistance having an impedance higher than the parasitic impedances to the body; the gate of each FET being coupled to a respective control voltage through a respective resistance having an impedance higher than the parasitic impedances to the gate; each FET being biased to operate in its linear region; and a FET gate control circuit controlling the gate of each field effect device responsive to an attenuator control signal, the FET gate control turning on the FETs in the shunt variable resistors and turning off the FETs in the series variable resistors progressively and at predetermined rates to monotonically increase the attenuation of the AC signal from a minimum to a maximum attenuation, and turning off the FETs in the shunt variable resistors and turning on the FETs in the series variable resistors progressively and at predetermined rates to monotonically decrease the attenuation of the AC signal from the maximum attenuation to the minimum attenuation.