Table of Contents
Understanding how to build and analyze BJT differential amplifiers is essential for electronics students and professionals. These amplifiers are fundamental in analog circuit design, offering high gain and good common-mode rejection. This article covers the practical steps involved in constructing a differential amplifier and analyzing its performance.
Basics of BJT Differential Amplifiers
A BJT differential amplifier uses two bipolar junction transistors (BJTs) to amplify the difference between two input signals. It is characterized by high gain and ability to reject common-mode signals. The circuit typically includes a current source, two BJTs, and load resistors.
Building the Circuit
To build a differential amplifier, start with a stable power supply and a constant current source. Connect the emitters of two BJTs to this current source. The bases serve as input terminals, while the collectors connect to load resistors tied to the power supply. Proper biasing ensures the transistors operate in the active region.
Analyzing Performance
Performance analysis involves calculating the differential gain, common-mode rejection ratio (CMRR), and input/output impedances. The differential gain depends on the load resistors and transistor parameters. Testing the circuit with varying input signals helps verify theoretical calculations.
Key Parameters and Testing
- Input voltage range
- Output voltage swing
- Gain stability
- Common-mode rejection