Tuesday, July 8, 2014

Amplifier Circuit Analysis in Orcad Capture

               A signal booster is basically an amplifier or an amplifying circuit that raises the signal (voltage/current) in the circuit output. When an signal is received via an antenna, the amplifying circuit connected to an antenna is a signal booster that raises the amplitude level of the input signal voltage or current.

 The following shows a circuit that amplifies signal voltage of a signal in the frequency range of 100KHz to 30MHz.

Signal booster Schematic

The circuit consist of as an AC source with amplitude or 0.1V and frequency of 1MHz modelling the receiver antenna. This received signal is amplified by multistage amplifier to make voltage gain larger. There are 3 transistors performing the voltage gain, MPF102 FET transistors and two bipolar transistors 2N3904 and 2N3906. The FET transistor an a voltage amplifier, the first bipolar transistor 2N3904 is also a voltage amplifier and the second bipolar transistor 2N3906 is a emitter follower. The total voltage gain is the multiplication of the individual voltage gains of each amplifier. In the circuit the resistors forms the biasing circuit for the transistors and the capacitors are bypass capacitors.

The circuit simulation of AC signal from antenna with gain amplifier to amplify the signal was obtained using AC sweep analysis where frequency was sweep from 100KHz to 30MHz. The voltage gain expression is 20* LOG10(V(Vout)/V(Vin)). Writing this in the trace expression gives the following graph-

voltage gain

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