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

Why do I need to run ac simulation on bangap refernce?

Status
Not open for further replies.
S

sharas

Member level 4
Joined
Jun 7, 2005
Messages
74
Helped
3
Reputation
6
Reaction score
0
Trophy points
1,286
Activity points
1,965
Please excuse this questio, which I'm sure most of you will regard as stupid: bangap reference circuit is intended to produce a stable DC voltage. Why is there any need to check the ac behaviour? What are the pitfalls?


Thanks,


Sharas
 

You can learn two important things.

The first is the transfer function between the power supply and the reference output. This will tell you the effects of noise on the power supply.

The second is the output impedance at different frequencies. This will tell you the effects of a load which draws a varying, periodic current or the effects of a step in load current.
 

    S

    sharas

    Points: 2
    Helpful Answer Positive Rating
cause there is a) feedback b) amplifier combined it could start oscillating
 

    S

    sharas

    Points: 2
    Helpful Answer Positive Rating
oscillating is a important fator in designing a bandgap.so you must check AC analysis.
 

    S

    sharas

    Points: 2
    Helpful Answer Positive Rating
Thanks for your answers, guys.

flatulent, do you mean that my reference voltage will change with the frequency due to the change of the output impedance? and regarding the noise in the power supply - isn't it enough to perform a DC sweep of +-10% of my the power supply and check that the output voltage is stable?
 

Yes, any circuit with a finite output impedance will change voltage with load current. Usually the impedance increases with frquency.
 

    S

    sharas

    Points: 2
    Helpful Answer Positive Rating
sharas said:
and regarding the noise in the power supply - isn't it enough to perform a DC sweep of +-10% of my the power supply and check that the output voltage is stable?
Click to expand...

DC sweep always considers all capacitors to be open. So you do not know how a time varying noise signal on the power line gets transferred to the output. So you need to do an AC analysis or a Noise analysis.
 

    S

    sharas

    Points: 2
    Helpful Answer Positive Rating
In the bandgap reference, it has a closed-loop negative feedback. When the disturbance signal is injected in the loop,the circuit probably will oscillator.So u must do ac analysis.
 

    S

    sharas

    Points: 2
    Helpful Answer Positive Rating
if you use opamp in your bandgap
u should simulate its phase margin and GBW
your bandgap should have enough PM to prevent oscillation and large GBW to have good transient respone
 

    S

    sharas

    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