Comparative studies have been carried out for the different types of signal amplifiers to find their performance characteristics with respect to circuit topologies, gain calculations, and merits and demerits of them. Studies have also been done to find their suitable applications in various fields. With respect to circuit topologies, the circuit diagrams are shown with single BJT to multiple BJTs; differential mode to push-pull mode and BJT to MOSFET with PMOS and NMOS and CMOS. Then, the use of an operational amplifier (OPAM) circuit to an operational trans-conductance amplifier (OTA) circuit. The biasing of the amplifier is considered as voltage bias or current bias with resistors or diodes. The gain of the amplifier is generally expressed as the ratio of the amplitudes of the output and input signals. It can be given as voltage gain, current gain or power gain (in dB) or in terms of trans-conductance. On the basis of the advantages and dis-advantages, each signal amplifier has its own application in the different fields based on its suitable performance with respect to low power consumption, optimum gain, good bandwidth, optimum weight and space ratio and good frequency response. The discussion has been made and conclusion has been drawn for this investigation.