Reference Voltages in ADC

[gunturikishore]

badgap accuracy reference for adc

Hi ,

I need atleast three stable refernce voltages in my ADC design which are 35omV, 500 mV and 800 mV. I tried a Band Gap reference circuit with pnp transistors but the voltage reference is about 1.3 V and I have no clue how to genertate these three reference sources from that.

Can anybody help me with some some reference papers or suggestions.

 

[wdd]

malcovati jssc

Commonly, based on you bandgap add a resistor string and three unit buffers

 

[elbadry]

You have two options to do what you want:

1. As gunturikishore pointed out. Buffer the output signal and apply it to a resistor string to get the voltage you need.

2. Generate a Sub-bandgap voltage using another famous core. You can find it in the following papers:

* Curvature-compensated BiCMOS bandgap with 1-V supply voltage
Malcovati, P.; Maloberti, F.; Fiocchi, C.; Pruzzi, M.;
Solid-State Circuits, IEEE Journal of
Volume 36, Issue 7, July 2001 Page(s):1076 - 1081

* 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

 

[megzhuy]

You can use the buffer to get the three different output voltage, but in real ADC design, it's always more difficult than this. You can find some papers of reference buffer. You need to see some datasheet to check the spec of your design.

 

[qutang]

using buffer op maybe simply.

 

[dhasmana]

You can design a 0.35V bandgap and then levelshift up the voltage to derive the higher voltages by buffering the bandgap voltage.

"A CMOS voltage reference based on weighted delta Vgs for CMOS low dropout linear regulators"
IEEE JSSC Vol 38 No. 1 Jan 2003.

Regards.
Dhasmana.

 

[hung_wai_ming@hotmail.com]

Ppl always said to use buffer to generate reference voltage. In reality, if you can check some company's ADC, you may find that they generate references only by resistor string. Why? Because bandgap generate noises to references in high accuracy ADC, and ppl finally prefer to use resistor string.

 

[dhasmana]

Hi Hung,

Why does the bandgap has more noise than resistor strings?The bandgap noise can be filtered also and then converted, but separate circuitary would be needed for that...
Please explain.
Regards,
Dhasmana.

 

[hung_wai_ming@hotmail.com]

1/f noise which cannot be reduced if you have op-amp based or bandgap based circuits.
What I mean is if you have application that works at low frequency like DC measurement or audio application, like ADC/DAC, then your reference got to be clean under low frequency

 

[bkat]

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