Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic 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 bais the error-amp in the Bandgap circuit?

Status
Not open for further replies.

benchen

Member level 2
Joined
Sep 9, 2005
Messages
42
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,286
Activity points
1,605
voltage divieder bais

The error -amp in the Bandgap needs the biasing current or voltage, I wonder how to get it? If we use the PAPT current of the bandgap as the biasing current, there is a new problem which is how to start up this error amplifier?
 

JT

Junior Member level 1
Joined
Dec 20, 2005
Messages
18
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,281
Activity points
1,474
I find it pretty hard to apply self biasing and still have a
-stable bandgap circuit
-good start up behavior

It can be done, but I prefer simple resistor + current mirror biasing,
plain and simple, and it always works.
 

qslazio

Full Member level 3
Joined
May 23, 2004
Messages
176
Helped
18
Reputation
36
Reaction score
7
Trophy points
1,298
Activity points
1,420
for the error amp, We always use self-biased structure(etc. vgs/R or simple dioded voltage divider).
I think the best structure for the amp is simple current mirror load diff-pair with a cascode output stage. And the compensation is made inside the amp.

anyone has ideas about it?
 

J

jiangwp

Guest
benchen:

you are right.
The PTAT current which consists of BandGap that can be used to bias the erro amplifier.

I think the sequence is :

PTAT is ready, then erro amplifier is working normally after biases is ready by feedback.

Maybe, the response speed is not so fast. But, generally, it is enough.

There is not any problem.

I have taped out a chip like this structure.
 

benchen

Member level 2
Joined
Sep 9, 2005
Messages
42
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,286
Activity points
1,605
Use simple voltage divider to bias the amp is Ok, but I found the PSRR is poor. Using the PTAT to bias the error ampilfier, the circuit is hard to start up correctly. jiangwap, can you show me an example of this circuit?
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top