Noise characteristics of stroboscopic transducers built with GaAs microcircuit integration

Stroboscopic transducers are used for measuring electric signals over a wide frequency range, the sensitivity of these devices being largely determined by the equivalent input noise voltage. The internal noise level can be appreciably lowered and the performance of such a transducer correspondingly improved by GaAs microcircuit integration of the input stage. A chip of 1x1 sq mm area can carry a mixer bridge of four Schottky-barrier diodes, a storing capacitor with discharge circuit, and a voltage repeater on Schottky-gate field-effect transistors, shot noise in the mixer diodes, and flicker noise in the diodes as well as in the voltage repeater. Two noise mechanisms are identified, corresponding to the two modes of transducer operation: mixer noise alone during strobing, mixer noise with noise in the discharge circuit and in the voltage repeater during measurement of widened pulses. The resultant spectral noise density is calculated on the basis of these identifications and corresponding equivalent circuit diagrams. During strobing the flicker noise appears as a multiplicative component and its deviation from the 1/omega law determines its lower frequency limit. During measurement of a widened pulse the noise is limited to the pass band of the output amplifier-integrator stage and a low-pass filter before this stage becomes desirable.