In the power amplifier circuit shown if the input is an RF sine wave, with VDD=1.8V and Vgs = 1V, what will be the waveform at the drain of the MOSFET - sine or square wave? Is it possible to get a sine wave at the drain?
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1\$\begingroup\$ Quick answer: Sinewave. More precise answer: a distorted sinewave but nowhere anything close to a square wave. L1 and C1 form a resonant tank which will attenuate frequencies outside the passband so even though M1 can be pushing a squarewave shaped current into the tank, the resulting voltage will be much more sinusoidal. How much depends on the Q of the tank. \$\endgroup\$– BimpelrekkieCommented May 19, 2017 at 14:41
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1\$\begingroup\$ Get a sim and simulate. \$\endgroup\$– Andy akaCommented May 19, 2017 at 15:16
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If the Rout of M1 is high, and Q of LC is high, you will build up the stored energy in that resonator, for a large sinusoid.
answered May 19, 2017 at 18:45