Please teach me. I have seen many analog circuits but lack a detailed understanding. There was a slack question about why a circuit with a current mirror didn’t simulate as expected. Ideally, a current mirror should duplicate the reference current from the reference mosfet in the output mosfet of the same size with the same Vgs. However, there are obvious exceptions. For example, if the drain of the output mosfet is open, there will be zero current no matter what the current in reference mosfet. Conversely, if the drain of the output mosfet is directly connected to a power source through a fixed resistor, a fixed current could create a voltage drop greater than the power source (eg. Voltage source=2V, I=1mA, R=10KΩ - according to Ohm’s Law, the voltage drop across the resistor should be 10V.) I read some explanations on the web, but are the following statements correct? 1. The reference mosfet (and corresponding output mosfet) works better if L>W to avoid short gate modulation. 2. Vgd of the reference mosfet should be roughly equal to Vgd of the output mosfet. 3. Should the input resistance be lower or higher than the output resistance? If so, what are the valid range of operation. @Abdalkreem Kasasbeh https://open-source-silicon.slack.com/archives/C017P3RAD42/p1695824940018579?thread_ts=1695813223.798899&cid=C017P3RAD42

1. L>W is not necessary. W*L defines the matching between both MOSFET, and L>Lmin is often done to lower gds on the output MOSFET.

@Harald Pretl I got the result I am looking for "the current and the gm" as shown in the photo but I needed to make Wm5 =2Wm10 and Wm6=Wm10, m10 and m6 have almost the same vds but mf5 has a higher vds. what I know is the the mirror transistors must be the same but here m10 and m5 are not the same

Put net labels on all mos drains so you see the drain voltage. Drain voltage of M5 is probably too low. Replace M1 and M2 with 01v8_lvt and use bigger W size. This will leave more voltage at M5 drain and bring it into saturation. Also NEVER use minimum length for current mirrors, so M10, M5, M6, M3, M4, M7, M9 should have much longer gates, say 0.8. Use bigger W (say 3 to 5) You see M10 Vgs is 0.81V, so M1 and M2 Vgs is also around 0.8V, leaving only 0.1V on M5 drain. See how Id is different if biasing the drain at 0.8V (M10) and at 0.1V (M5) for a very short transistor.

@Harald Pretl thanks for the response! For number 3, I was assuming the the pull up resistance on the reference mosfet should be roughly equal to the resistance seen by the output mosfet. I was wondering if that assumption was correct and at what relative output resistances does the current mirror cease to function as a current mirror.

@Stefan Schippers thank you very much it is much better now after considering your advice

@Mitch Bailey Usually input to MOSFET is a current source. For cheap biasing a resistor will do (as you mention). However, there is no relationship between resistor and input and at output. The output impedance is ideally infininite, realistic 1/g_ds of output MOSFET. Small-signal at input MOSFET is 1/g_m.