Qualitative and Tuning Performance of MOSFET Based Small-Signal Darlington pair Amplifiers

Two different circuit models of RC coupled small-signal amplifiers are developed using identical power MOSFETs in Darlington pair configuration. Proposed circuits successfully eliminate the poor frequency response problem of Darlington pair amplifiers at higher frequencies. An additional biasing resistance RA, ranging from 1KΩ to 100KΩ, is to be essentially used in the proposed circuits to maintain their voltage/current amplification property. In presence of RA, proposed amplifiers crop considerably high voltage gains, moderate range bandwidths and sufficiently high current gains in 1-10mV input signal range at 1 KHz frequency. Both the circuits can be tuned in specific audible frequency range, extending approximately from 130Hz to 55KHz. Tuning performance makes these amplifier circuits suitable to use in Radio and TV receivers. The qualitative and tuning performance offer a flexible application to these amplifiers to be used as high voltage gain, high power gain and tuned amplifiers. Variations in voltage gain as a function of frequency and different biasing resistances, temperature dependency of performance parameters, bandwidth and total harmonic distortion of the amplifiers are also perused to provide a wide spectrum to the qualitative studies.