Electronic Devices and Circuits Engineering Sciences 154

Issues in Design of Multi-stage Amplifiers:

Why do we need multistages?

Compared to single stage amplifier, multistage amplifiers provide increased input resistance, reduced output resistance, increased gain, and increased power handling capability

 

Multistage amplifiers commonly implemented on integrated circuits where large numbers of transistors with common (matched) parameters are available.

 

Typical inverter (Common Emitter) has moderately large gain and has input and output resistances in the Kilohm range.

 

Follower configuration has much higher input resistance, lower output resistance but has only unity gain.

 

Amplifier requires the desirable features of both configurations

Desirable conponent single-stage characteristics

741 Example

Differential to Single-ended Conversion

Differential cascade
Example 1
Example 2

DC Level Shifting:

In DC coupled multistage cascade the output bias level of each stage increases to maintain the collector more positive than the base (constant current operation).  If this voltage ìstackingî is severe, little swing room is left in the final stages of the cascade

• Use of Zener or (ordinary) diode level-shifters (source):
Three stage amplifier with one diode
Three stage amplifier with two diodes

• Use of complimentary npn/pnp BJTs:
A two stage Tranconductance Amplifier (source)

• Use of complimentary NMOS/PMOS FETs:
A two stage CS amplifier (source)