Current Mirror Calculator
Calculate current mirror output current, beta error, reference resistor, power consumption, and Widlar mirror resistor for analog IC and bias circuit design
Formula
I_out = N × I_ref × β/(β+2), R_ref = (V_CC − V_BE) / I_ref
How It Works
A current mirror is a fundamental circuit configuration in analog electronics that provides a simple and precise method of copying or replicating a reference current to another part of a circuit. It typically consists of two transistors, where one transistor (the reference transistor) establishes a specific current, and the second transistor precisely mirrors that current with high accuracy. This technique is crucial in integrated circuit design for creating constant current sources, current scaling, and building more complex analog circuits.
Worked Example
Consider a current mirror with a reference transistor Q1 having a bias current of 1 mA and a matched transistor Q2. If R1 = 10 kΩ and the supply voltage is 5V, calculate the mirrored current: First, determine the base-emitter voltage (Vbe) needed to establish 1 mA through Q1. Then, configure Q2 to replicate this exact current by ensuring identical transistor characteristics. The resulting current through Q2 would be 1 mA, demonstrating the current mirror's precise current replication capability.
Practical Tips
- ✓Ensure transistors are closely matched or from the same integrated circuit
- ✓Maintain consistent temperature and operating conditions
- ✓Use high-quality, low-noise transistors for precision
- ✓Consider using bandgap references for more stable current generation
Common Mistakes
- ✗Neglecting transistor parameter variations
- ✗Ignoring temperature effects on current mirroring
- ✗Using mismatched transistors
- ✗Failing to provide adequate bias voltage
Frequently Asked Questions
What is the primary purpose of a current mirror?
To generate a precise, controlled current that is a replica of a reference current, useful in analog circuit design and current-based signal processing.
Can current mirrors work with different transistor types?
Best results are achieved with matched transistors, typically from the same integrated circuit or with very similar characteristics.
What factors affect current mirror accuracy?
Temperature, transistor matching, power supply stability, and circuit design all impact the accuracy of current mirroring.
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