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How do I start to design this bandgap circuit?

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shaq

shaq

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Dear all,

I want to design a 0.6v of Vref in the bandgap as shown below.

But, I have a question that is how do I determine the (W/L) of each transistor?

And, how to determine the current of each transistor?

Thanks so much!!!!!

(Tech. Process is TSMC 0.18um, Vdd is 1.8v)
 

It's a very useful question.
Who will answer this question ?
 

Why do you want to use this structure only for your bandgap?
 

This is a bandgap CKT without Resistors, but it is not suitable for trimming
 

ipsc said:
Why do you want to use this structure only for your bandgap?
Click to expand...

Because this structure is simple and I don't need to design opamp and resistor.
 

it is better for you to use normal bandgap with reisitor to design a product
 

This is a bandgap CKT without Resistors, but it is not suitable for trimming
Click to expand...

Why? And what is CKT?


it is better for you to use normal bandgap with reisitor to design a product
Click to expand...
Why? I think resistors can't be made with precise value. Why not avoid them and use all transistors?

Thanks.
 

yorande said:
This is a bandgap CKT without Resistors, but it is not suitable for trimming
Click to expand...

Why? And what is CKT?

CKT means circuit.


it is better for you to use normal bandgap with reisitor to design a product
Click to expand...
Why? I think resistors can't be made with precise value. Why not avoid them and use all transistors?

Thanks.
Click to expand...
 

yorande said:
This is a bandgap CKT without Resistors, but it is not suitable for trimming
Click to expand...

Why? And what is CKT?


it is better for you to use normal bandgap with reisitor to design a product
Click to expand...
Why? I think resistors can't be made with precise value. Why not avoid them and use all transistors?

Thanks.
Click to expand...

we use resistor for bandgap
 

I have the same question during the bandgap design
 

Why do you use this type of bandgap? What benefits do the circuit have? We often use the conventional bandgap with resistor.
 

This circuit won't work well for you. Even in the original paper, I believe this kind of circuit is just a trick for wirting a paper. Nobody uses it in the product (because your gm also has temp/ process variation). The vout is mainly relied on a DC point Vd2 plus a ac amout of k*delta(Vd), not better than a simple resistor one in any textbook.
In your new figure, you put a third diode in order to get 0.6V output. The total output would be: Vd2+k*delta(Vd)-Vd3. You just add two delta(Vbe), then you won't have temperature compensation.
In the orignal paper, If you cannot make sure the current flowing through M4 and M1 are ratioed (which is hardly to control in the reality, due to the mismatch), then the equation of vout won't hold. And the ratio of squareroot (AG) won't do better job than a resistor pair (which can be ratioed well).
Just my thought, don't mean to offend the author.




shaq said:
ipsc said:
Why do you want to use this structure only for your bandgap?
Click to expand...

Because this structure is simple and I don't need to design opamp and resistor.
Click to expand...
 

I guess this new bandgap can generate lower Vref than conventional one, which outputs 1.2x V.

BTW, is this new design really a bandgap? Any references for it? Thanks.
 

bandgap is a normal design
 

shaq said:
ipsc said:
Why do you want to use this structure only for your bandgap?
Click to expand...

Because this structure is simple and I don't need to design opamp and resistor.
Click to expand...
Hi,

unless you are compelled to do this only, I feel it's better to switch to conventional BJT's based one. Because the one you posted has no industrail or commercial importance. As quoted in one of the posts
the mos parameters are not well controlled, so the variation in your reference will be large.

for a ieee paper, it's fun to see how many different references you can make to get your name published. when you're shipping 1,000,000 units/month you are not interested in fun, only yield.
Click to expand...

And moreover conventional based 0.6V bandgap is also a very challenging one. Finally, your effort will be worthy if you spend it on designing BJT based bandgap.

Regards
 

do the bandgap without resistor have no industrail or commercial value in the future?
 

If you need a bandgap lower than a conventional (~1.22V) one, I would recommend reading the following paper:

A CMOS bandgap reference circuit with sub-1-V operation
Banba, H.; Shiga, H.; Umezawa, A.; Miyaba, T.; Tanzawa, T.; Atsumi, S.; Sakui, K.;
Solid-State Circuits, IEEE Journal of
Volume 34, Issue 5, May 1999 Page(s):670 - 674
Digital Object Identifier 10.1109/4.760378
 

I have the same question during the bandgap design too!!!
 

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