High-Pass Filter with Transistor

The circuit

Because of circuit simplicity, an additional example of a high-pass filter with a transistor as an emitter follower is shown bellow. The calculated slope differs slightly from -12dB/octave, but this is the price of having a simplified circuit version.

The input file (high-pass_filter_with_transistor.cir)

high-pass filter with transistor

* fo = 1 / (2 pi (r1 r2 c1 c2)^(1 / 2))    Cutoff Frequency
* d = (1 + c2 / c1) (r1 c1 / (4 r2 c2))    Damping Coefficient

.control
set units = degrees
ac dec 50 10Hz 100kHz
plot vdb(4) vp(4) xlabel f[Hz] ylabel 'magnitude[dB] phase[degree]'
  + title 'AC analysis'
.endc

v1 8 0 dc 10V
v2 6 0 dc -10V
v3 1 0 dc 0 ac 1

r1 2 4 10k
r2 3 0 39k
r3 4 6 10k

c1 1 2 10nF
c2 2 3 10nF

q1 8 3 4 bjtn

.model bjtn npn

.end

The results