Hello everyone. Please cirticise my op amp design....
# analog-designa
Aswin
08/18/2024, 1:16 PMHello everyone. Please cirticise my op amp design.
I am attaching the circuit operating points and gain bode plot for VCM of 0.9 and 1.6 Volts.
I think my transistors are over sized - I have no prior experience, please tell me.
Note that I have not attached the phase plots, because I have a question, how do I obtain phase margin from ngspice CLI?
Thanks
l
Luis Henrique Rodovalho
08/18/2024, 9:38 PMTransistors M0 and M5 are a current mirror. Try to size them with the same width and length, but different number of parallel transistors to make non unity current gains. Try to use at least two parallel transistors with half transistor width. It keeps the aspect ratio the same, but you will be able to use interdigitation and common centroid layout techniques later. Matching is very important for analog circuits, and you must design them taking the actual layout into consideration.
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Luis Henrique Rodovalho
08/18/2024, 9:41 PMhttps://github.com/lhrodovalho/sky130_rodovalho_ip__lpopamp/blob/main/xschem/tb_lpopamp_open_ac.sch
Look at this testbench. This is how I use ngspice controls to measure AC performance, such as low frequency gain, phase marging, cmrr, and psrr.
Luis Henrique Rodovalho
08/18/2024, 9:43 PMLuis Henrique Rodovalho
08/18/2024, 9:47 PMYou should simulate your amplifier as a unity gain buffer, or voltage follower. Differential amplifiers are not normally used without some kind of negative feedback. Try to make a subcircuit and a symbol for your design, so you can reuse the same design in other testbenches, or reuse the same testbench with other designs.
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Aswin
08/19/2024, 4:10 AMThank you Luis. I will do that.
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