Wave transmission lines and networks – Attenuators
Patent
1987-12-11
1989-06-06
Gensler, Paul
Wave transmission lines and networks
Attenuators
307568, 333262, H01P 122
Patent
active
048375306
ABSTRACT:
A FET variable absorptive attenuator utilizes FETs as variable resistors controlled by voltages applied to their gate terminals, the FETs preferably being arranged in a T configuration with resistors connected in parallel with two series FETs, as well as a shunt FET in the form of a distributed shunt FET. One control voltage adjusts the resistances of the series FETs, and another controls the resistance of the distributed shunt FET. A proper combination of the two control voltages yields a desired level of attenuation with optimum input/output impedance matching. The resistors allow the series FETs to be biased well below their pinch-off voltages to minimize the parasitic capacitances of the series FETs at relatively high attenuation settings, improving the isolation for high attenuation settings at relatively high frequencies and also enabling the attenuator to function as a switch. They also improve the power-handling capability at high attenuation settings. The distributed shunt FET is split into several cells interconnected by inductive elements, providing a low insertion loss at maximum attenuation, as well as decreasing the parasitic capacitance of the shunt FET. The effects of this lower capacitance at relatively low attenuation settings can be more effectively counteracted by the inductive elements, extending the dynamic range of attenuation at relatively high frequencies. Also, the distributed shunt FET interconnected by the inductive elements compensates for the parasitic capacitances of the series FETs at relatively high attenuation settings, which yields increased attenuation with increasing frequency. Finally, the cutoff frequency of the attenuator at relatively low attenuation settings is increased.
REFERENCES:
patent: 3921106 (1975-11-01), Williams
patent: 4097827 (1978-06-01), Williams
patent: 4523161 (1985-06-01), Miles
patent: 4733203 (1988-03-01), Ayasli
Ayasli, Microwave Switching With GaAs FETs, Microwave Journal, Nov. 1982, pp. 61-74, TK-7800 M5 333-104.
Gensler Paul
Hewlett--Packard Company
Milks, III William C.
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