Abstract
AbstractThe conductance of the reactance circuit used in the tuning circuit of the CR tuned amplifier is a function of frequency with negative minimum value. If the external parallel resistance to the tuning circuit is reduced so that a high selectivity is obtained, the conductance becomes negative at a frequency other than the resonance frequency and the circuit will oscillate. We have obtained a stable high‐gain tuned amplifier with high selectivity by selecting the values of resistor and capacitor in the voltage phase‐shift circuit so that the conductance of the tuning circuit is minimum at the resonance frequency. The amplifier with the resonance frequency of 10 kHz fabricated according to this design method exhibits the maximum selectivity of about 700 and the voltage gain of about 100 dB. These values agree well with the computed values. The rate of change of the resonance frequency for the temperature has been made rather small with the use of circuit components with small temperature coefficients. However, the rate of change of the gain (and hence selectivity) is extremely large. With the use of an ac resistive circuit with a positive temperature coefficient consisting of PTC thermistors and transistors, the rate has been reduced to the extent tolerable in the practical temperature range.
Published Version
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