Attenuator with compensation of impedance errors

Abstract

Step attenuators wherein a number of individual attenuators are connected in series, with a switch across each individual attenuator, are well known. By opening and closing particular combinations of the switches, any one of a number of different values of attenuation may be selected. Each individual attenuator has in the past, as well as in the present invention, had a characteristic impedance equal to the impedance of both the signal generator (which feeds the input of the step attenuator) and the load (connected across the output of the step attenuator). However, the switches for selecting the individual attenuators may have substantial resistance especially where solid state switching diodes or mercury wetted reed relays are employed. The latter type switches display resistances caused by skin effect at highter frequencies. This causes inaccuracies of the attenuation steps due to mismatch, in prior art systems of the type described above. To avoid the mismatch, an additional impedance is added to the circuit, between each adjacent pair of attenuators, to form a network. The network includes the resistance of the switches. This network is designed to have a characteristic impedance equal to the characteristic impedance of each attenuator. Stated otherwise, it has the same characteristic impedance as the impedance of the signal generator and the impedance of the load.

Dependencies are inferred from the claim text.