Design fully differential telescopic OPAMP(single stage only)
a) Analysis of all equations of your design, with a
systematic derivative of all transistors W/L ratios
and spectre simulation of circuit for the following
specifications.
i) Open loop gain(DC gain) ≥ 80 dB
ii) UGB ≥ 300 MHz
iii) Differential Output voltage swing ≥ 3V
technology 0.18um

Can somebody tell me procedure to bias the circuit and schematic of it. I am trying to bias the circuit but unable to understand the concept behind the calculation of W/L ratio.Can you explain?It will be appreciated if somebody does analyse and calculate W/L values.
Is it necessary to use CMFB to bias the circuit.

Hi,
I implemented the fully differential telescopic opamp with cmfb circuit . I got a gain of 85dB voltage swing more than 3V but UGB is 80Mhz . Any ideas on how to increase the UGB of the opamp?
Power consumption should be less than 3mW and Vdd is 3.3V

schematic of the circuit that i used.how to decide the bias point ?

Quote:


You seem to be avoiding the most important question...are C0 and C1 the load?

loose-electron wrote on Mar 26^th, 2014, 11:20am:

Hell, this place would implode if everyone did that.  ;)

I don't know why books "calculate" W/L. Mostly what you need to know is that gm =~ 2I/(Vgs-Vt) in strong inversion. In weak inversion gm becomes largely independent of Vgs-Vt so maximum gm will be ~I/75mV.

This is an approximation, but now you have gm in terms of I and Vgs-Vt, which are the only physical design variables that you can change. I is limited by power, and Vgs-Vt is limited to ~150mV for the diff pair and by headroom requirements for the loads and cascodes.

UNITY GAIN Bandwidth is =gm/Cload/2pi =~ so maximum bandwidth is (I/75mV)/Cload/2pi.

From this you can determine how much current you need to achieve your desired UNITY GAIN bandwidth for a given capacitive load. If you are close you can see if you can get enough gm in weak inversion (realizing your input devices are going to get very wide and increase the input capacitance), but if you are off by a factor of two you either have to relax your power requirements and increase I, or decrease your load capacitance. You don't have any other options.

I emphasized UNITY GAIN because if you are configured for a higher gain your bandwidth will be scaled by your feedback factor.

I'm sure there is a paper or book out there that covers this way of designing but I'm not aware of it.

rg