Help needed with fully differential amplifier design

[Sudeep Banerji]

Hi guys

I need to design a fully differential amplifier having CMFB with a large Gain Bandwidth product of around 3Ghz. Also the settling time has to be less than 5ns. Closed loop gain is 15. Can a folded cascode achieve this in 180nm technology? Would I need two stages? Please advice on the topologies which can be considered. Thanks!

 

[Dominik Przyborowski]

3 GHz is quite high bandwidth. The question is about load capacitance and power consumption constraints.
RFC with additional features could be a good choice - for the last 4 years it was the main way to performance improvements (check papers for 2011-2014).
To ensure stability also feedforward compensation technique could be useful.

With two stages it will be very hard to obtain 3 GHz of GBW.

 

[Sudeep Banerji]

Hey Dominik

Thanks for the speedy reply and your insights. As for the power and load capacitance it is 10mW and around 60fF. I'll check out RFC and related papers and try to come up with something. Thanks!

 

[Dominik Przyborowski]

OK. So You have 5 mA to biasing whole opamp, it's should be high enough to do this with classical folded cascode.

 

[Sudeep Banerji]

Cool! I'll try it out thanks!