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CACD Group updated 2000.03.30 Author Janez Puhan |
Low-Pass Filter with TransistorThe circuitThe ideal active device (voltage controlled voltage source) from previous example is replaced with a transistor acting as a unity gain emitter follower in this example. Simulation shows that the frequency response agrees with the graph from previous example at up to ten times the cutoff frequency. At higher frequencies, attenuation is limited to a value depending on the output impedance of the bipolar transistor. The input file (low-pass_filter_with_transistor.cir)low-pass filter with transistor * f0 = 1 / (2 pi (r1 r2 c1 c2)^(1 / 2)) Cutoff Frequency * d = (1 + r1 / r2) (r1 c2 / (4 r2 c1)) Damping Coefficient .control set units = degrees ac dec 50 100Hz 100kHz plot vdb(4) vp(4) xlabel f[Hz] ylabel 'magnitude[dB] phase[degree]' + title 'AC analysis' .endc v1 5 0 dc 10V v2 6 0 dc -10V v3 1 0 dc 0 ac 1 r1 1 2 10k r2 2 3 10k r3 4 6 10k c1 2 4 39nF c2 3 0 10nF q1 5 3 4 bjtn .model bjtn npn .end The results |
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