Basic Current Mirror
Category: Analog Circuits
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This is a simple and basic current mirror circuit. In this circuit you will learn how current mirror circuit works. 1. There are four types of BJT current mirror circuits. a) Basic current mirror circuit. b) Beta helper current circuit. c) Widlar current (source) mirror circuit. d) Wilson Current mirror circuit. 2. This is a basic current mirror circuit. 3. Ideally a pair of matched BJTs fabricated (on same wafer) in close proximity to each other so that their characteristics should be same. 4. Ideally the beta of both transistors Q1 and Q2 should be same. Then current flowing through load will be equal to the reference current (Iref), because the base current is same and Ic = Beta*Ib. 5. But in practical if we use two separate transistors of same number, there beta will be different, thats why the current flowing from Q1 and Q2 will be different but they follow constant ratio or constant offset as shown in animation. Applications: 1. This circuit is used to understand the basic current mirror circuit. 2. This circuit can be used to find the beta of each transistor. 3. This circuit is used to make constant or adjustable current control. Notes: 1. This circuit is designed and simulated in proteus 7.10. 2. The other 3 types of current mirror circuit will be uploaded soon.