High-resolution dc-voltage-biased ac conductance bridge for tunnel junction measurements
- 1 July 1979
- journal article
- Published by AIP Publishing in Review of Scientific Instruments
- Vol. 50 (7) , 903-908
- https://doi.org/10.1063/1.1135947
Abstract
A simple, low-cost conductance bridge circuit, which provides high-resolution measurements of dI/dV and d 2I/dV2 for a voltage-biased load, is presented. A resolution in dI/dV for a 90-Omega tunnel junction of several parts in 10(5) has been measured using a 35-microV-rms modulation level and a 1-s postdetection time constant (Bn=0.25 Hz). The output impedance of the voltage source and the error in the conductance measurement are discussed. The output impedance of the circuit with an AD119 operational amplifier is 0.02 Omega. A detailed discussion of Johnson-Nyquist, tunnel junction, and amplifier noise is presented.Keywords
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