PROBLEM 102 · Easy · A fault in: basic current mirror
Broken Mirror
A mirror that copies nothing
The problem
The circuit on the canvas was built for the problem “Basic current mirror”, but it does not meet the specification. The output current does not follow the reference at all.
Find what is wrong and repair it: change a value, move a wire or add a part. Everything the original problem asked for still applies (the targets are listed below), and the live readings and the colours of the transistors will show you where to look. Check your circuit when you think it is fixed.
The test bench
- Supply: VDD = 1.8 V.
- Your reference is the Current source you place: set it to 50 µA.
- The test bench holds the net named “out” at 0.9 V with a voltage source, sweeps it from 0.1 V to 1.7 V, and measures the current your mirror exchanges with it.
Numbers to hit
- Output current at 0.9 V between 97 µA and 103 µA
- Change between 0.5 V and 1.5 V at most 6 %
- Every transistor in saturation
Design it yourself
Draw the circuit on a schematic canvas, size every transistor, and see it simulated in your browser with ngspice and the SkyWater SKY130 models. Every transistor lights up green, gold or red by operating region as you move the sliders.
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