A multistage amplifier using two or more single stage common emitter emitter amplifier is called as cascaded amplifier. A multistage amplifier with common emitter as the first stage and common base as second stage is called cascode amplifier.

In Multi-stage amplifiers, the output of first stage is coupled to the input of next stage using a coupling device. These coupling devices can usually be a capacitor or a transformer. This process of joining two amplifier stages using a coupling device can be called as Cascading.

Depending upon the type of coupling, the multistage amplifiers are classified as: 1. Resistance and Capacitance Coupled Amplifiers (RC Coupled) 2. Transformer Coupled Amplifiers 3.

In the study of multistage amplifiers, we shall frequently come across the terms gain, frequency response, decibel gain and bandwidth. These terms stand discussed below : (i) Gain. The ratio of the output *electrical quantity to the input one of the amplifier is called its gain.

MULTISTAGE AMPLIFIERS. Definition: An amplifier formed by connecting several amplifiers in cascaded arrangement such that output of one amplifier becomes the input of other whose output becomes input of next and so on . Each amplifier in this configuration is known as stage.

There are two primary advantages of cascade amplifiers: increased gain and input, and output impedance flexibility. The need for the gains provided by cascade amplifiers is paramount to the functionality of various applications.

The cascade amplifier advantages are:

• Enhanced performance and efficiency.
• Maximum flatness levels.
• Minimal noise figure in the range of 1-10GHz.
• Increased gain.
• Increased bandwidth allows the devices to be widely employed for high-voltage amplifier purposes.
• Hight input and output impedances.

The high frequency response of multistage amplifiers theory is used for high gain as well as high bandwidth.

The overall reason for cascading amplifiers is the need for an increase in amplifier output to meet a specific requirement, e.g., to increase the signal strength in a Television or radio receiver. Using a cascade, or multistage, amplifier can provide your design with a higher current gain or voltage gain.

When a multistage amplifier is to amplify d.c. signal, then one must use coupling.

When they are coupled to make a multistage amplifier, the high output impedance of one stage comes in parallel with the low input impedance of next stage. Hence, effective load resistance is decreased. This problem can be overcome by a transformer coupled amplifier.

The current gain of this amplifier is equivalent to the product of the current gain result of separate stages The advantages of the multistage amplifier are flexibility within input & output impedance and higher gain. The multistage amplifier applications are, it can be used to increase extremely weak signals to utilizable levels.

Multi-Stage Transistor Amplifier. In practical applications, the output of a single state amplifier is usually insufficient, though it is a voltage or power amplifier. Hence they are replaced by Multi-stage transistor amplifiers. In Multi-stage amplifiers, the output of first stage is coupled to the input of next stage using a coupling device.

The coupling capacitor passes the AC from the output of one stage to the input of its next stage. While blocking the DC components from DC bias voltages to effect the next stage. Let us get into the details of this method of coupling in the coming chapters.

In this type of coupling, the signal expands across the main winding of the transformer and it performs as a load. The minor winding moves the AC o/p signal straight toward the base terminal of the next stage. This method enhances the total gain & matching level impedance.