Most transistor layouts in the textbooks are only concerned with W/L > 1 layouts. For good matching, they use interdigitated fingers. For a current mirror layout, can anyone suggest a good layout topology if W1/L1 = 4/20 and W2/L2 = 1/20 ?
I am not sure how to address this issue.
If you design low power circuits. I think you still layout like finger. The width is finger in W/L > 1 transistor, but in your transistor length is finger.
JarryZhao, thank you very much for your suggested layout, this has helped me understand how to design long length current mirror ratio.
Laglead, i use a W/L << 1 as my circuit is a low-power low-bandwidth (10kHz) amplifier. It is low-frequency because I need to amplify biopotential signals. It needs to be low-power as it is going to be imbedded in the human body as part of an ASIC.
As my application is for low level signals, should I place guard rings around all of my functional blocks, i.e., all diff pair, all current mirrors etc?
U can put guard rings around all, But you should better use a power or GND only for guard rings. The guard rings power only for guard rings, not connect any circuits.