Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

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

Status
Not open for further replies.
L

lilac

Junior Member level 1
Junior Member level 1
Joined
Jan 26, 2005
Messages
18
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,281
Activity points
229
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!
 

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.
 

    L

    lilac

    Points: 2
    Helpful Answer Positive Rating
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
 

    L

    lilac

    Points: 2
    Helpful Answer Positive Rating
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?
 

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.
 

    L

    lilac

    Points: 2
    Helpful Answer Positive Rating
design of ota for high gbw

j2005 said:
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.
Click to expand...

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
 

    L

    lilac

    Points: 2
    Helpful Answer Positive Rating
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.
 

    L

    lilac

    Points: 2
    Helpful Answer Positive Rating
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.
 

    L

    lilac

    Points: 2
    Helpful Answer Positive Rating
how to increase gbw of op amp

lilac said:
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?
Click to expand...
Have you added a resistor in series with the compensation capacitor to cancel zero?
 

    L

    lilac

    Points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top