Bridge measurement of tunnel-diode parameters

A specific bridge measurement technique is presented for measuring the important small-signal parameters of the tunnel diode at frequencies up to 100 Mc and at all significant operating levels. Particular attention is paid to the problem of biasing the tunnel diode to eliminate instability in the negative resistance region which would otherwise prevent significant measurements being made in this region. Requirements for stable bias circuits are analyzed in detail and specific criteria for stable operation given. A circle diagram method is presented which allows the significant parameters to be determined from a set of measurements made for a sequence of bias voltages, at a chosen frequency. From the results, curves of shunt capacitance and conductance as a function of bias voltage may be plotted. Measurements made using a Wayne Kerr Type B.801 VHF Admittance Bridge on a particular tunnel diode are presented. The experimentally determined capacitance vs voltage curve is found to agree closely with the theoretical curve of the normal junction diode, with no pecularities through the negative resistance region. Further results show that approximate parameter values may be obtained even when oscillatory or bistable behavior prevents satisfactory measurement in the negative resistance region.