Internal and External Reference voltage for a DAC

[Somil]

Hi

I am talking in general about the Reference voltage in a DAC.

Say For example: If we are using +10V as the internal reference voltage, the range of the DAC would be -10 to +10V. But if the signal goes only from -5 to +5 V, the resolution of DAC is not getting maximized. To maximize the Resolution, an external refernce voltage of +5V can be given. Now the range of the DAQ will be -5V to +5V, same as that of the signal..

What is internal and external reference voltage for DAC ?????

[Mark_SAI]

Hello,

Internal reference voltages are something on-board the DAC that can be switched on easily by programming it. External reference voltages are something you connect externally to the DAC IC from a stable power source.

Note to get your +5V to -5V range you gave as an example, you would need +5V on the positive reference and -5V on the negative reference IF the DAC supports that. Normally the range would only be between +5V and 0V if you only gave the DAC a +5V reference.

I hope this information helps!

[Somil]

Thanks for the reply.

Mark, in case of 6251 DAQ, the range of the voltage is from -10V to +10V. This means, i will get maximum resolution for my signal only when the signal goes from -10 voltage level to +10 voltage level. However, if my signal lies in between the voltage range -5 to +5V range, then do i need to connect an external reference voltage of +5V in order to get a maximum resolution signa???

And 1 thing more, can i connect some voltage level different than this. I mean for a signal of -5V to +5V, can i connect a reference voltage say 2V or 9V?

[Mark_SAI]

Hello,

This will explain it in more detail, I believe it answers your question!

[Somil]

Oh, i am getting more confused now.

I have read that for getting higher resolution, the signal must cover the entire range of the DAQ device. For this , we even go for the amplification of the signal.

But this states that halving the range will give you twice as good resolution.

[Mark_SAI]

Hello,

Example:

If I have a signal going from +5v to -5v on a 10-bit DAC where the reference is set up to +5v and -5v, the voltage between steps is about 10mV per step. If I then half the range, my new signal will go from +2.5V to -2.5V on a 10-bit DAC where the reference is set up to +2.5v and -2.5v, the voltage between steps is about 5mV.

Message Edited by macaba on 09-08-2009 05:30 AM

[Somil]

OK!!!!

The whole thing revolves around Reference voltage only. Had i halved the range without halving the reference voltage, then the resolution of the signal would have gone poor. So, can i say that reference voltage is used to set the voltage level between two successive steps ,as in your example, halving the reference voltage also changed the resolution voltage level from 10mv to 5mv thus giving a higher resolution.