Operational Amplifier - Design

[whirl7wind77]

Can anyone tell me,
how to design a high speed, low power ( < 20 uW ) Operational Amplifier ( with supply voltage 1.2 V in 90nm CMOS ) ?

 

[Dominik Przyborowski]

As fast as possible.

You need to choose a proper architecture and to make trade-off between output swing, gain and speed.
Probably the best architecture will be recycled telescopic or folded cascode with degenerated current sources, gain boosting and feedforward compensation.

 

[whirl7wind77]

I knew that. I found in literature that the telescopic one has low power consumption and high speed.
But I could not achieve high speed and 20 uW power consumption. Can you suggest architecture ?

 

[nitishn5]

You might need a 2nd stage with good driving capability to get the high speed.
Telescopic in itself with the limited current budget would have limited bandwidth to provide the speed.

I am assuming the by speed you mean the response to switching loads. Try a second stage as a driver which consumes minimum current in DC but is able to drive high current steps.

 

[Dominik Przyborowski]

Try to use recycled arcitecture, it is harder to design than classic cascode but provides around 20-40% improvment in bandwidth.

Look for this papers:
**broken link removed**
https://link.springer.com/article/10.1007/s10470-011-9762-y
https://iopscience.iop.org/1674-4926/33/2/025002

 

[an_82]

Telescopic opamp is a good choice for high-speed and low-power consumption. You can find design steps thoroughly in the following book:

Behzad Razavi, Design of Analog CMOS Integrated Circuits, Pages: 299-300

Also I attached the schematic of the circuit.

 

[whirl7wind77]

Hi an_82,
This is the first circuit I tried. My supply voltage is 1.2 V.
This circuit has a problem maintaining bias points. It consumes hundreds of uW power.

 

[Dominik Przyborowski]

This circuit has a problem maintaining bias points. It consumes hundreds of uW power.

So You doing it wrong...
The tail current source determine the power consumption in telescopic cascode. If You set proper W/L ratio for transistors in current mirror You get not more current than You assume.