[SOLVED] TSMC 0.35 UM problem: bulk/substrate connection

[shockingshockley]

in tsmc 0.35, I have designed an op amp with dual supplies of +/-2.5V with bulk/substrates connected to vss(-2.5V). Meanwhile, I designed a comparator which uses a single supply of +5V/0V with bulk connected to GND. When I connected the output of the opamp to the comparator's input, the output of the comparator is pretty bad. Is it because the bulk/substrate are shorted with different voltages? (-2.5V and GND 0V?) What are other solutions???

Because I need an output of 5V and 0V. Thank you!!!! Hoped for your immediate reply.

 

[erikl]

In a real CMOS process (on p-substrate), the substrate must always be at the most negative voltage level. So your opAmp and comparator connection is ok (opAmp's -2.5V is identical to comparator's 0V = GND = substrate). Now just forget about the opAmp's ±2.5V supply and call it a 0 to +5V supply, too, same as the comparator's.

I suppose you have to supply the opAmp's inputs with a voltage level of about +2.5V in this case, which you usually realize by appropriate DC feedBack from the output. If your opAmp's input common mode range (ICMR) and OCMR is large enough, by this method you can probably adjust its quiescent output voltage to a required value, which is fine for the necessary comparator input voltage level.

If this isn't possible because your opAmp's ICMR or OCMR aren't large enough, you need some appropriate DC level adjustment between the opAmp's output and the comparator's input. If it's an ac application, this should easily be possible by capacitive coupling.

If you need more help, you better post your schematics.

BTW: Ever thought of combining both the opAmp and comp functions into the same opAmp application?

 

[shockingshockley]

hi erikl,
Thanks or your immediate reply. I understand some points you have addressed.

Actually for the comparator, I used the same subcircuit of the opamp meaning the opamp and comparator share the same subcircuit.
(I used the cmos designed opamp as a comparator [single supply of 5V/0V])
Attached here is my spice file for your viewing.

I am very new to ic design so I badly need your help.

 

[shockingshockley]

I have solved the problem by supplying 0.6/0.7V in the negative input of comparator instead of connecting it to the ground.