Thermal noise in junction-gate field-effect transistors

Measurements are reported on the device parameters and the noise properties of junction-gate field-effect transistors and the results are compared with theory. It is found that the high-frequency input conductance g
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and the high-frequency gate-drain conductance g
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vary as the square of the frequency and show practically full thermal noise. The high-frequency transconductance decreases with increasing frequency, as expected theoretically. The high-frequency output noise of the FET for short-circuited input is the sum of the low-frequency noise of the FET and the thermal noise of |g
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|. A small correlation effect between the short-circuit gate noise and the short-circuit drain noise exists and agrees with theory. An approximate expression for the noise figure is given that is reasonably correct up to the cutoff frequency of the FET.