Will an MOS based active sinusoidal oscillator work for higher operating frequencies or BJT based?
The bipolar transistors can work at higher frequencies than the MOS transistors. The bipolar transistors has much higher transconductance than the MOS transistor and it has lower parasitic capacitance and resistances.
The maximum operating frequency which is the unity gain bandwidth called fT is given by
fT= gm/2pi C , c is the cgs in the MOS transistor and cbe in the bipolar transistor.
fT of the bipolar transistor is greater than that of the MOS transistor provided they have the same technology generation,
With scaling down the dimensions of the MOS transistor its fT increases and approaching that bipolar transistor.
Best wishes
Applications of MESFETs were initially in microwave circuits for high frequency performance, generally in the range of 1 to 10 gigahertz. As hole mobility in GaAs is 5 to 10 times higher than it is in Silicon and allows MESFET operation at frequencies higher than can be achieved with Silicon devices.
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