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Design >> Analog Design >> How to design this circuit?????
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Message started by E20314006 on Dec 7^th, 2009, 3:56am

Title: How to design this circuit?????
Post by E20314006 on Dec 7^th, 2009, 3:56am

Hi, friends,
Can anyone tell me some steps of designing this bandgap circuit below, assuming the desired specifications are given?
Must the mismatch between resistors and BJTs, the offset of OPAMP, the noise from all components be considered,during the design?
How to considered these nonideal impacts, and how to select the OPAMP?
More details are expected.....Thanks !!!!1

Title: Re: How to design this circuit?????
Post by Mayank on Dec 8^th, 2009, 6:15am

Hello,

Quote:

Can anyone tell me some steps of designing this bandgap circuit below, assuming the desired specifications are given?

I think you should study BG design further from different textbooks. Start with razavi, & then move onto Rincon Moora. These should provide you a good enough understanding of the subject and design procedure.

Quote:

Must the mismatch between resistors and BJTs, the offset of OPAMP, the noise from all components be considered,during the design?

Yes All Mismatches, offsets, noise are considered in an industrial standard BG Design.

Quote:

How to considered these nonideal impacts, and how to select the OPAMP?

There's math behind everything. Search some papers / reading material on Voltage References, you will find it.
Opamp selection depends on your PSRR profile, and then the amount of noise injected by the error amplifying loop.

-mayank.

Title: Re: How to design this circuit?????
Post by raja.cedt on Dec 9^th, 2009, 2:18am

hi E20314006,
i didn't understand why you have chosen this kind of architecture? why ayou are loding your opamp with resisters. What i feel is you have to drive mosfets rather than resisters, in case you are using mosfet current sources then better to chose opamp based on psrr and systamatic offset point of view. So generally pmos current sources are driven by opamp whose load is pmos so as to get good psrr. Better use this pap
.V. Gupta, G. A. Rincon-Mora, and P. Raha, "Analysis and Design of Monolithic, High PSR, Linear Regulators for SoC Applications," Proc. IEEE International System on Chip (SOC) Conference, pp. 311-315, Santa Clara, California, 2004.

Thanks,
Rajasekhar.

Title: Re: How to design this circuit?????
Post by E20314006 on Dec 10^th, 2009, 1:55am

Mayank wrote on Dec 8^th, 2009, 6:15am:

Yes All Mismatches, offsets, noise are considered in an industrial standard BG Design........
There's math behind everything. Search some papers / reading material on Voltage References, you will find it.................

Thanks,Mayank for detail reply.
Should I write some equations about these nonideal impact on the bandgap'performance before designing the bandgap, and then design the circuit according to these equations? Is it all right?
Can you give me some paper about it? Thank you!

raja.cedt wrote on Dec 9^th, 2009, 2:18am:

...What i feel is you have to drive mosfets rather than resisters, in case you are using mosfet current sources then better to chose opamp based on psrr and systamatic offset point of view. So generally pmos current sources are driven by opamp whose load is pmos so as to get good psrr. Better use this pap
.V. Gupta, G. A. Rincon-Mora, and P. Raha, "Analysis .........

Thanks, raja.cedt .
So , I first study available OPAMP'PSRR and offset,and then select an OPAMP according to these and the desired OPAMP'specification, is it all right???
But how to identify the OPAMP'PSRR and Offset according to the bandgap specification???? Some papers or materials are expected!!!
Thanks!!!!!