help me about oscillations on my bandgap reference circuit!!

[universeee]

i am designing a bandgap circuit for my graduation project. i have to take a fix voltage, as you know, between 0.4-0.6V and this voltage must be independent of supply voltage, which is 1V min and 3.3V max for my project from 0C to 80C degree.
when i achieve my goals at 3.3V, voltages on my circuit at 1V oscillates or vice versa.
what can i do about these oscillations???

here is the topology: **broken link removed**
and i attached the topology

please help me...
thanx from now...[/url]

 

[yschuang]

Re: help me about oscillations on my bandgap reference circu

There is a positive feedback loop around V1 and M1.
Imagine OTA+M1 as a two-stages amplifier.
Then you probably know what to do.

 

[universeee]

Re: help me about oscillations on my bandgap reference circu

There is a positive feedback loop around V1 and M1.
Imagine OTA+M1 as a two-stages amplifier.
Then you probably know what to do.

actually i could not imagine what i must do, can you be more clear please??
because i have always problem about understanding feedback loops...
thanx from now...

 

[yschuang]

Re: help me about oscillations on my bandgap reference circu

Hi, there

Please take a look at the follwoing reference.

DESIGN OF A 1.5-V HIGH-ORDER CURVATURE-COMPENSATED CMOS BANDGAP REFERENCE By Philip K. T. Mok

 

[rfzheng]

as far as i am concerned , you should first check your OTA, if it is stable and how much phase margin it has？

put a suitable capacitor between supply and your OTA output, it may help to stablize the reference and it will aslo do some good to your reference's PSRR.

 

[kwkam]

I believe 1V may be too low for your bg circuit function properly. You may imagine that the lowest work voltage is Vbe + Vds. And this voltage may be margin for 1V. I suggest you can adjust the current level and increase the length of MOS

 

[universeee]

Re: help me about oscillations on my bandgap reference circu

thanx for your answers you all... i guess i handled the problem by changing the resistor values and W/L ratio of several transistors. my circuit produces oscillations according to high resistor values and low W/L ratios.