bipolar signaling
Bipolar transistor circuit analysis problem?
Circuit diagram provided in the address below
(please remove the spaces in the address to get the correct address)
freewebs .com/ alexander3133 /circuit3. jpg
From the circuit you can see there is a capacitor C1 connected between collector and the base.
The input voltage is about 0.3V sine waves at 1kHz and the measured output voltage is about 0.5V sine waves with phase shift, this indicates that the input signal is actually amplified. How to explain this voltage amplification with the present of C1 capacitor? Maybe explain how the capacitor function as?
Normally what I studied was the circuit above without the C1 capacitor, therefore the additional capacitor made me confused.
http://www.freewebs.com/alexander3133/circuit3.jpg
0.5 volts p-p is not much gain. You are bypassing a lot of your signal to the collector. You might have current gain, with some voltage gain from what small amount of of the 1 KHz is getting into the base to be amplified. If the capacitor is intended as a bypass for certain frequencies, which this is the usual case, then to gain more signal out, change the value of the capacitor to have a much higher impedance to 1 KHz so that this signal is not bypassed to the collector. What you do have, actually, is a beating of the base signal and the bypassed signal at the collector. The 2 are fighting each other. The signal through the capacitor is bucking the signal that is being amplified that is being fed to the base junction.
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