Vbias in 2-stage OP Amp circuit

[bpazolli]

When I look at circuits of a two stage op-amp CMOS model, I often see a Vbias terminal. My question is how this is connected up in the final circuit as often when we take the operational amplifier as a single block we only have the +'ve and -'ve inputs and the output. The only understanding I have of this Vbias term is that it should be the average of the two input's. However that maybe incorrect.

 

[godfreyl]

Isn't Vbias the bias voltage for something like a cascode? Can you show an example circuit?

 

[bpazolli]

Isn't Vbias the bias voltage for something like a cascode? Can you show an example circuit?

**broken link removed**

 

[godfreyl]

In this case Vbias is the bias voltage for the current sources (M5 and M7). There needs to be extra circuitry on the chip to provide that voltage. Sometimes details like that are left out for simplicity. i.e. This is a simplified schematic, not a full schematic.