GATE Electrical – Analog Electronics
Page 23 : Wilson Current Mirror
The Wilson Current Mirror is an improved version of the basic current mirror that provides better current accuracy and higher output resistance.
It uses three transistors instead of two and reduces the error caused by base currents.
Why Wilson Current Mirror?
In a simple current mirror, the output current is slightly smaller than the reference current because of base current losses.
The Wilson current mirror compensates for this error.
Circuit Structure
- Three matched transistors (Q1, Q2, Q3)
- Reference resistor R
- Feedback connection through Q3
The third transistor provides feedback that stabilizes the output current.
Working Principle
The circuit works by feeding back the collector current through the third transistor. This feedback increases the effective output resistance and improves current accuracy.
As a result:
Iout ≈ Iref
with much smaller error compared to the simple current mirror.
Advantages
- Higher output resistance
- Improved current accuracy
- Reduced base current error
- Better current stability
Applications
- Analog integrated circuits
- Operational amplifiers
- Precision current sources
- Bias circuits in IC design
Important GATE Points
- Wilson current mirror uses three transistors.
- Provides higher output resistance.
- Improves current mirror accuracy.
- Widely used in analog IC design.
Next Page → Operational Amplifier (Op-Amp) Introduction
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