FETs as Variable Resistors

Fig. 7 is a schematic diagram of the electronic attenuator. Two pairs of field-effect transistors are the variable resistors. The bias voltage (E in Figs. 5 and 6) is quite low 20 mV so the FET's operate in the linear regions of their V-I characteristics, and therefore look like resistors. The resistance of each branch varies from about 30 Q to 1 MQ. The direct current flowing through the FET's (I in Figs. 5 and 6) is an accurate measure of the rms value of the ac input signal, provided that...

Robert F C Vessot

Bob Vessot received his B.S., M.S., and Ph.D. degrees in physics from McGill University in 1951, 1954, and 1957. From 1956 to 1960 he was a staff member at the Massachusetts Institute of Technology, where he worked on cesium-beam frequency standards and a cold-helium-gas-moderated cesium maser. In 1960, he joined the Beverly group then Varian Associates, now HP and initiated a program concerned with the newly invented atomic hydrogen maser. He is now manager of maser development. Along with N....

New Log Converter

Ac or dc signals whose amplitudes vary over exceptionally wide ranges as much as 80 dB four decades, Fig. 1. New model 7562A Logarithmic Converter can be used with Model 3300A 3305A Sweep Oscillator to make frequency response plots over an 80 dB amplitude range and a four-decade frequency range. The converter produces a dc output voltage proportional to the logarithm of the rms value of an ac input signal. Its frequency range is 0.5 Hz to 100 kHz. It can also convert dc signals. HP 203A...

John M Wade

John Wade is a group leader for laboratory X-Y plotters and accessory instruments with HP's San Diego Division formerly Moseley Division . He has been designing recorders and related instruments since he joined HP in 1961. He has worked on line followers, a keyboard, recorder time bases, recorders, and plotting systems, and has designed three logarithmic converters including fhe 7562A. He has a patent pending on the electronic attenuator used in the 7562A. John received his B.S. degree in...