How to design a high-gain, wide GBW Opamp?

[lilac]

high gbw op

I need a Opamp with DC gain>80dB and Unity Gain frequency >100MHz. At first I try to design it with the class-A two-stage structure. but it is difficult to satifiy both the DC gain and phase margin.
Who can give me some advice about how to design. such as, if class-A structure can meet the request, or which kind of structure is more suitable. and so on. Thanks in advance!

 

[jiangwp]

highi gbw opam

May be the folded-cascode can meet the requriement.

First , the GBW is the function of power and technology(line width).

From the vlaue of Gain and GBW , the dominant pole is placed larger than the 10Mhz.

you can use two stage folded-cascode to split the requriement of Gain and GBW.

The first stage supply large current to enhance the transconductance and increase output resistance that results in the GBW incresing and the dominant shifting to large frequency.

The second stage supply the large Gain.

 

[borodenkov]

opamp gbw 1t

hi lilac,

many OTA architectures are suitable for your design. You have not mentioned several things about your OTA:
- power supply voltage & target technology (Vt of transistor)
- required output swing
- power dissipation requirement

 

[lilac]

wide gbw

Thank you. In fact the supply voltage is 3.3V, TSMC0.25 Process. (Vtn 0.52V, Vtp 0.85V) and load capacitance 1pF.
At first I set compensation capacitance to 250fF, but it seemed the phase margin is not enough(52), on the other hand if I increase the compensation capacitance, there seems a very large transistors must be adopted. So, do you have any suggestion?

 

[j2005]

ota how to increase gbw

I doubt you can get it to 100MHz UGBW and a DC gain at low frequencies of 80dB with CMOS. You'll need bipolar or bicmos for that.

 

[crazyamd]

design of ota for high gbw

I doubt you can get it to 100MHz UGBW and a DC gain at low frequencies of 80dB with CMOS. You'll need bipolar or bicmos for that.

of course you can. there're plenty of designs avaible for this kind of spec. it's NOT that hard. also, op needs to address other info like what is the load, power consumption, what is the amplifier for etc

 

[terryssw]

op amp gbw

If your output swing is not too tough, then try a folded-cascode with cascode boosting techniques, this shoud be provide you > 85 dB gain and > 150MHz GBW without too much problems. Or you can try two-stage opamp with first stage cascode structure, but this will consume much more power.

 

[lastdance]

150mhz high voltage opamp

As of your compensation, could you buffer the output load? to move the 2nd pole away? this may help to limit your size of Miller cap.

 

[whaler]

how to increase gbw of op amp

Thank you. In fact the supply voltage is 3.3V, TSMC0.25 Process. (Vtn 0.52V, Vtp 0.85V) and load capacitance 1pF.
At first I set compensation capacitance to 250fF, but it seemed the phase margin is not enough(52), on the other hand if I increase the compensation capacitance, there seems a very large transistors must be adopted. So, do you have any suggestion?

Have you added a resistor in series with the compensation capacitor to cancel zero?