How current mirror works
R1 establishes the reference current in diode-connected Q1. Matched Q2 sinks current through R2. Both transistor bases draw from the reference branch, so finite beta reduces the copied current. Q1’s beta applies to both matched transistors.
Matched generic transistors, VBE ≈ 0.7 V, no Early effect. Maintain at least 1 V at the output for the active-region estimate. Real matching, temperature and finite output resistance affect accuracy.
Change the form inputs or click a component value on the schematic. Choose Try in CircuitSim to simulate the configured circuit.