Experimental studies of frequency response and related properties of small-signal bipolar junction transistor amplifiers

Abstract Small-signal bipolar junction transistor (BJT) amplifiers, including common-emitter (C-E), common-base, and common-collector amplifiers, are the basic building blocks of many analog integrated circuits. An experimental investigation of the physical analysis of the frequency response and related parameters of these amplifiers have been performed in some details. The analysis uncovers fundamental reasons underlying the frequency response of the amplifiers. It indicates that although both the load resistance R L and the collector resistance R C , influence the voltage gain, for example, of a C-E amplifier, none of them should be very high to yield the highest value of the voltage gain. The distortion of the wave form of the output signal is found to be a serious problem in BJT amplifier circuits. This problem is particularly very serious in C-E amplifier with square wave signal and at high frequencies. Although by-pass capacitor plays a crucial role in minimizing this problem, the contribution of the coupling capacitors in this regard cannot be ruled out. Physical reasons of the distortion has been discussed in some details.