BJT current mirrors
Matched simple, Wilson and Widlar mirror estimates including base-current error.
Development preview. Check the assumptions below before relying on a result. Calculations run in your browser.
How it calculates
Widlar solution: ln(IC1/IO) = IO(1+1/β)RE/VT; IREF = IC1(1+1/β)+IO/β
Assumptions
- Matched transistor temperature, beta and saturation current. Nominal current excludes Early-effect mismatch.
- Feedback sink: Q1 emitter feeds RE to ground; Q2 senses the RE voltage and pulls down Q1 base. IREF feeds their shared base/collector node. IOUT approaches VBE(Q2)/RE; finite equal beta is included. Output resistance is not inferred without a full feedback model.
- Wilson current ratio and output resistance are first-order matched-device approximations; minimum compliance uses VBE + 0.2 V.
Worked example
These are the calculator's default inputs. Change any input above to recalculate.
Inputs
- Mirror
- simple
- Reference current
- 0.001 A
- Matched beta
- 100
- Widlar / feedback-sink emitter resistor
- 1000 Ω
- Early voltage
- 100 V
- Reference VBE
- 0.7 V
- Available output voltage
- 5 V
- Device temperature
- 25 °C
Results
- Output current
- 0.000980392 A
- Current error
- -1.96078 %
- Approximate minimum output voltage
- 0.2 V
- Approximate output resistance
- 102000 Ω
- Output-transistor dissipation
- 0.00490196 W