How to design Voltage referance using bandgap referance

[rocky.king07]

Hello everyone
I need three voltage references 1.4V, 1.65V and 1.9V for 14-bit pipelined ADC. My supply voltage is 3.3V (0.18u CMOS technology). I have a bandgap reference having reference voltage 1.2V. How I can generate 1.4V, 1.65V and 1.9V using 1.2V. Can anyone suggest a circuit for for generating reference voltages. Thanks.

 

[ducvilla]

I think you can use a structure like LDO: it means you need an error amplifier and use feedback network, then you can easy to get these above reference voltage.
Another advantages of this structure is if you use pipelined ADC, you must use a lot of resistors at the output stage of bandgap, => if these resistors have not enough value => Vref decreases much, => use LDO structure you can easily avoid this problem.

Hope this help!
Duc.

 

[erikl]

How I can generate 1.4V, 1.65V and 1.9V using 1.2V.

Use an opAmp with gain 1.9/1.2 and a resistor chain to tap off the two lower voltages.
If these two lower voltages have too high impedances (resp. are too noise-sensitive), use additional buffers.

 

[RobG]

You didn't mention if these references are supplied with external components or you have to generate them internally. For a pipeline the 1.4 V and 1.9 V references will probably need to be low impedance and very low noise so use an opamp or voltage regulator to create those. There are some papers that show how to create a differential reference if you want to do it more compactly inside of the chip. They should also be tightly coupled together; that is, the pipeline should (depending on the design) be able to tolerate some common mode bounce, but no differential bounce so a differential reference is better if possible. Be very aware of meeting the required noise requirement and settling time issues. You can achieve these with a fast low noise design or a slow design with lots of filtering. If you go with the slow design be aware of signal dependent loading which will require low DC resistance.

The 1.65 V is likely the agnd pin. Often you can tolerate more noise and less precision on this one and be able to use a voltage divider between the 1.4 V and 1.9 V refs.

rg

 

[rocky.king07]

I want to generate it inside. Can you please suggest me some paper for differential reference.

 

[erikl]

I want to generate it inside.

Here's a schematic for similar purpose:

 

[rocky.king07]

Thanks for your reply. Above ckt is very helpful for me. Also, if you have schematic of differential reference then kindly reply.

 

[snaildr]

I thought the point of BG ref is to be stable vs. temperature. If you use amplifiers to convert the voltage, wouldn't that make the voltage temperature dependent? I remember it's possible to build bandgap ref with different voltages. (originally the name of bandgap ref came from the fact you only build bandgap ref with voltage =~ bandgap, but that's not very correct actually)

 

[erikl]

Re: How to design Voltage reference using bandgap reference

I thought the point of BG ref is to be stable vs. temperature. If you use amplifiers to convert the voltage, wouldn't that make the voltage temperature dependent?

You're right of course: you need opAmps with a low TC and VC. Ours was good enough for an integrated voltage change < ½LSB for a 10bit converter over the industrial temperature and supply voltage range.