Learn about current mirrors - build your own !

Current mirrors are basic building block for audio amplifiers, opamps and much more. - Plug it into a breadboard, and integrate it with your DIY amplifier build.

This version is the Symmetric Wilson Current Mirror - Highly accurate!

https://analogtoolshub.com/current-mirrors/

https://en.wikipedia.org/wiki/Wilson_current_mirror

Regards R1 and R2

They act as emitter‑degeneration resistors.

These resistors improve accuracy by:

1) Making the V_BE - I_C relationship less transistor‑dependent

Small resistors convert variations in transistor beta, V_BE, or mismatch into small voltage differences across the resistors instead of across the transistors.

2) Improving the matching of Q1 and Q2

Even if Q1 and Q2 have slightly different V_BE or β, degenerating them with resistors forces the currents to equalize because:

I_C ≈ ( V_REF − V_BE ) / R_E

so variations in V_BE create smaller changes in I_C.

3) Reducing finite Early‑voltage effects

Emitter resistance increases the small‑signal output resistance of the mirror.

Typical V_BE mismatch in BJTs, in discrete parts: 

  ΔV_BE​​ = 1-5 mV

To reduce mismatch error to <1%, you want:

  R1 = R2 >> ΔV_BE​​ / I

Example - If ΔV_BE ≈ 5 mV and current is 1 mA:

  R >> 5 mV / 1 mA = 5 Ω

Common values in precision mirrors:

  R1 = R2 = 10-22 Ω