Single-stage Transistor Amplifier

Single-stage means one transistor and other auxiliary components. The circuit having one transistor-associated circuit is called a single-stage transistor amplifier.

Normally the single-stage Transistor amplifier is used to amplify the weak signal to the strongest signal. But the practical case the single-stage amplifier gives only a small voltage gain.

For the large amplification, we need a multi-stage amplifier and auxiliary components. The practical circuit has using multistage amplifiers and different types of transistors.

the Single-stage Transistor Amplifier circuit diagram and working explained

Single-stage Transistor Amplifier
Single-stage Transistor Amplifier

In the below-shown circuit diagram is the basic amplifier using a single transistor. Only when we understand the working of this single-stage amplifier circuit, can we understand the working of the multistage amplifier.

For example, you plan to make a single-stage amplifier, that situation you will need the full details of the circuit, so I will start to explain the all details.

Input is an AC signal, you need to connect the AC signal as input, you will set up the transistor as a biased condition. AC input can be given only in biased conditions.

Dc biasing means fixing the operation point in the middle of the active region. Different types of dc biasing are available but the best one is potential divider biasing (voltage divider). Because the operating point is stable in the temperature variation and the parameters are stable. So we have designed the biasing circuit using the potential divider biasing. The designed circuit is showing in blow.

This is the simple basic circuit diagram of the single-stage amplifier. The circuit has only 5 components and 3 input and output sections. A circuit diagram has connected the input on the base of the transistor. The input is a weak signal, but the output of the amplifier is strong. So the transistor has boosted the weak signal too strong.

The Vcc power supply connects through an R1 and Rc resistor and the output is taken on the collector pin of the transistor.

the Practical Circuit of single-stage Transistor Amplifier and explanation

Practical Circuit of single-stage Transistor Amplifier
Practical Circuit of single-stage Transistor Amplifier

This practical circuit is working on 5 different types of functions.

  1. Biasing Circuit
  2. Input Capacitor
  3. Emitter Bypass Capacitor
  4. Coupling Capacitor
  5. Load resistor RL

A practical single-stage amplifier is a combination of these four circuits.

  1. Biasing Circuit

The R1 and R2 and Re resistors are used biasing and stabilize the amplifier circuit

Resistors R1 and R2 are called biasing resistors, which will divide voltage of VCC and base of the transistor, and hence this circuit is called a voltage divider bias circuit

Different types of biasing circuits using BJT are fixed bias and collector to base bias but there is another very powerful circuit of biasing which is called voltage divider bias.

  1. Input Capacitor

The input capacitor Cin is a vital component for an amplifier circuit. This capacitor couples the input signal to the base of the transistor. The input capacitor Cin allows AC signals but isolates them from DC signals.

A capacitor is a passive electrical component that is used to store energy in the form of a field in a magnetic field in the form of an electric field.

Input capacitors are coupled to the input signal from the input signal source. The input capacitor Cin allows AC signals but isolates DC signals from entering into the transistor or into other circuit elements.

In the circuit, we are using a 10uf electrolytic capacitor as the Input Capacitor.

  1. Emitter Bypass Capacitor

The bypass capacitor is a type of capacitor that, as the name suggests, has a bypass function. The use of a bypass capacitor is to protect the circuit from excessive voltage.

A capacitor is usually employed in parallel to the emitter resistor RE. The amplified AC signal can then be passed through this type of capacitor, which will then help protect the circuit from excessive voltage and high-frequency currents.

 If you do not connect the bypass capacitor, the amplifier output voltage will be decreasing.

  1. Coupling Capacitor

A coupling capacitor does not do anything but connect one stage with another and block the dc voltage. The capacitor is present at the end of one stage and connects it to the input of the other stage.

It is called a coupling capacitor because it couples two stages together and helps them work together in order to transfer signals from one stage to another.

  1. Load resistor RL

The output is taken through a load represents the impedance of the actual load which is to be connected to the amplifier.

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