Hello, Jeph Daligdig ,

V_REF1 and V_REF2 are the required gate bias voltages for M5 and M6, such that they can act as DC current sources to provide the required DC currents for the paths they are connected to.

Once you decide about the values of those DC bias currents, you can create the required V_REF1 and V_REF2 voltages with help of refence current sources and diode connected copies of those MOSFETs (i.e. by forming current mirrors).

(I created a quick sketch of how the required connections can be. Sorry for the rough drawing)

While determining the DC currents and sizes of the MOSFETs, you should try to avoid "systematic offset" (You can find the relevant information from any CMOS analog design book).

Best regards...

Hello J.M Daligdig,

Those two voltages (V_REF1 and V_REF2) are fixed DC voltages that designers calculate to design the circuit. So when you want to design an operational amplifier with different tools (Synopsys, Cadence, etc) you just use an appropriate fixed number but in reality, you have to use another circuit to create that fixed voltages.

I recommend using Micro-Cap (http://www.spectrum-soft.com/download/download.shtm). All EE's at Emerson used Micro-cap, even though it cost $4,000 each. There are no other electronic SPICE modeling programs even close to Micro-Cap capability.

Micro-Cap is now free. Andy Thompson, owner of Spectrum Software, has retired.

Micro-Cap does worst case analysis --- changing the tolerances of components --- changing the temperature --- etc. And it is easy to use.

I have used Micro-Cap for all of my electronic designs since 2001. When I tested prototypes, they worked exactly as the model predicted.

The website --- https://NDAcademy.FoxPing.com/ --- 2.8 Electronic Cascade RC Filters --- and --- 7.2 Electronic SPICE Models --- provide examples.