brito.tb
Junior Member level 2

hi.Hi,
I am studying how to design an OTA, as reference I am using the book CMOS Analog Circuit Design from Allen. But I have some questions that isn't explained in the book. How can I calculate the bias voltages showed in this figure?
View attachment 56831
Thanks
Thanks for the answer BradtheRad, but my really doubt is about how to calculate the bias voltages like Vnb1, Vnb2, Vpb1 e Vpb2. I already calculated the sizes of the transistors following the book of Allen. But there isn't explain how to calculate the bias voltages. Anyone knows how to?The diagram illustrates concept of operation. The icons are enhancement mode which is more commonly used than depletion mode.
N-channel mosfets are the ones with the arrow in the lower leg (or source terminal). So this means you would apply input voltages ranging between zero and +5v to operate their gates. Gate V is referenced to source terminal.
If you apply 0V to the gate it will cause the mosfet to show high impedance across source and drain terminals.
If you apply 5V or more to the gate it will cause the mosfet to be 0.1 ohm or so.
Adjust proportionately for figures in between.
As for the P-mosfets they are identified by the arrow in the upper leg (or drain terminal). So you would apply between VDD and VDD-5 to operate their gates. Gate V is referenced to the drain terminal.
Say the VDD is 12V. Then the P-channel mosfets operate on gate voltages from 7V to 12V.
Apply 12 V to the gate and it causes the mosfet to show high resistance.
Apply 7V or less to the gate and it causes the mosfet to be 0.1 ohm.
Adjust proportionately for figures in between.
These are ballpark figures of operation.
This could be a case where the author presupposes certain prior knowledge on the part of the reader.Thanks for the answer BradtheRad, but my really doubt is about how to calculate the bias voltages like Vnb1, Vnb2, Vpb1 e Vpb2. I already calculated the sizes of the transistors following the book of Allen. But there isn't explain how to calculate the bias voltages. Anyone knows how to?