A Solid-State Variable Resistor Using a Junction FET

A noncontact variable resistor having fast response and small nonlinear distortion is needed for applications such as autoattenuators or autoequalizers. For these purposes, the voltage controlled variable resistor (VCR) based on the junction FET was investigated. This paper describes the-design results achieved by a VCR and also discusses the behavior of this device with regard to nonlinear distortion and aging characteristics. S/D
2
and S/D
3
(S: signal level; D
2
, D
3
: second and third harmonics level) were over 70 dB in the resistance region of 40-600
\Omega
and were improved by 10-30 dB, compared with the conventional FET. Resistance aging is less than 1 percent at 100°C after 1000 h.