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Small-Signal Amplifier with JFETs in Triple Darlington Topology

SachchidaNand Shukla

New circuit model of small-signal amplifier with three identical JFETs in Triple Darlington topology is proposed and qualitatively analyzed for the first time. Unlike CS-JFET amplifiers, the voltage gain of the proposed circuit is found considerably higher than unity. This amplifier successfully scales signal excursions swinging in 1- 35mV range at 1KHz frequency. In wide-band performance range (7.59MHz bandwidth), the proposed amplifier simultaneously produces high voltage and current gains (18.039 and 150.729 respectively) with considerably low THD (0.22%). These properties offer a flexible application range to the proposed circuit as high-voltage-gain wide-band amplifier in 42Hz-7MHz frequency range. An additional biasing resistance RA (ranging in 250Ω-100KΩ) is to be essentially used in the proposed circuit to maintain its voltage/current amplification property. This amplifier can also be tuned in specific range of audible frequency which explores its suitability to use in Radio and TV receiver stages. Small-signal AC analysis of the circuit, variations in voltage gain as a function of frequency and different biasing resistances, temperature dependency of performance parameters like voltage gain, bandwidth, current gain and total harmonic distortion of the amplifier are widely studied to observe a wide spectrum of qualitative performance.