Miller effect with 2N3904 PUBLIC

Looking at the Miller effect in the context of bandwidth, using two configurations of BJT amplifier.

Config'n 1: one BJT, Common Emitter 2N3904.

Config'n 2: two BJTs cascode, Common Emitter and Common Base, 2 x 2N3904.

There are two gain levels: approx 10dBV and 34dBV. Gain control is by means of the Emitter decoupling capacitors C6 and C7. Their values are selected in the Frequency Domain simulation by parameter Edec.

The high gain is unrealistic for a practical circuit but emphasises the point.

C8 is not necessary for functional operation, but evens up the exact gain levels in the two configurations by making the impedances at base1 and base2 the same.

R1 and R14 are not necessary for functional operation but isolate the inputs from each other.

From the F-D plots:

1] Hi gain -3dBV points for Configs 1 & 2 are 160kHZ and 2.8MHz,

2] gain-bandwidths at 0dB for 34dBV gain are: Config1: 8Mhz; Config2: 32MHz.

3] gain-bandwidths at 0dB for 10dBV gain are: Config1: 5Mhz; Config2: 14MHz.