How to decide on the values of a set of resistors for a circuit?
This circuit will provide gain of 100, yet with substantial distortion for inputs larger than a few milliVolts input







simulate this circuit &ndash; Schematic created using CircuitLab

The values of R2+R3, being approximately beta*R1, causes the Vce to be approximately VDD/2 or 5/2 = 2.5 volts. The voltage across R1 is also 2.5v, thus current thru R1 is 2.5 milliAmps.

The 2.5mA makes the gm be 0.1 amps per volt.

The voltage gain is gm * R1, ignoring all other parasitics acting in parallel with R1 (such are Early Effect and Rload and R2).

The voltage gain, computed as gm * R1, is 100.

Notice the dimensions on gm: amps per volt, and the dimensions on the resistor: volts per amp, cancel each other when multiplied, leaving the gain to be a pure ratio; more properly, delta volts in becomes delta volts out.

Many assumptions are in this circuit. But the DC-feedback of R2, C1, R3 does ensure this circuit will self-bias and let some signal through. In fact, FETs may even work in this circuit.