An amplifier circuit diagram consists of a signal pick-up transducer, followed by small signal amplifier(s), a large signal amplifier and an output transducer. Initially, there are two type of amplifier circuit diagram is in practical i.e. voltage amplifier circuit and power amplifier circuit.
Voltage amplifier circuit:
The primary function of the voltage amplifier circuit is to raise the voltage level of the signal. It is designed to achieve the largest possible gain. Only very little power can be drawn from the output. In order to achieve high voltage amplification the voltage amplifier circuit must fulfill following requirement.
- The transducer having thin base i.e. the transistor with high Î² (exceeding 100) are used.
- Input impedance is quite low in comparison of output impedance.
- Voltage amplifier always operates at low collector current nearly in order of 1mA because to permit high collector load, which is necessary to have high voltage gain.
- Mostly R-C couple is preferred for coupling various stage of voltage amplifier circuit because of cheaper in cost and portability.
Power amplifier Circuit:
Power amplifier circuit is meant to raise the power level of the input signal. In order to get large power at the output, it is necessary that the input-signal voltage is large. That is why, in an electronic system, a voltage amplifier circuit always precedes a power amplifier circuit, as shown in block diagram of amplifier circuit (Figure 1). This is why power amplifier circuit is also called large signal amplifier circuit.
The region behind power amplifier circuit called large signal amplifier circuit is because it draws power from DC source connected in output and converts it into suitable sine wave or AC signal. Power amplification is impossible because it is against the rule of physics. In order to achieve high power amplification the circuit must fulfill following requirement.
- In power amplification, heat is produce in transistor during operation, so large sized power transistor as far as possible is used.
- Transistor having thick base not as voltage amplifier (smaller Î²) are used in order to handle large current.
- Mostly transformer-couple is used for impedance matching.
- Collector resistance made low.