Voltage Shifter or Voltage Translator

Thread Starter

fieryfire

Joined Feb 14, 2017
150
Dear All,

I am looking to use a DAC which is the AD5672R. But this is a unipolar DAC that outputs values from 0 to 2.5V. But i would like to translate the values into a bipolar range at -1.25V to +1.25V. Could you please suggest a simple technique to do this?i do not think that the AD5672R works on bipolar rails. Is there some kind of method you could propose to convert from unipolar to bipolar ? Thank you
 

Thread Starter

fieryfire

Joined Feb 14, 2017
150
Wow. Thanks a lot eric. I also came across the following document from TI. that talks about this subject. Im amazed at how fast you can realize circuits. You must have very strong basics. I feel like a complete noob in comparison :)

For your question. I have the flexibility to use any op amp.
http://www.ti.com/lit/ug/slau525/slau525.pdf
 

Thread Starter

fieryfire

Joined Feb 14, 2017
150
Wow. Thanks a lot eric. I also came across the following document from TI. that talks about this subject. Im amazed at how fast you can realize circuits. You must have very strong basics. I feel like a complete noob in comparison :)

For your question. I have the flexibility to use any op amp.
http://www.ti.com/lit/ug/slau525/slau525.pdf
I hate to disturb you again on this. but after following the equations from the above reference. It does not work if i need to convert the scale from say 0 to 2.5V to a bipolar output between -20m to +20m. Is it possible to convert it from your circuit. or would it be better to use a voltage divider at the output
 

ericgibbs

Joined Jan 29, 2010
18,766
hi,
Can you say how the +/-20mV will be used.?
You will require a very stable OPA etc to maintain a +/-20mV Vout for a 0V to +2.5Vin.
E
 

Thread Starter

fieryfire

Joined Feb 14, 2017
150
hi,
Can you say how the +/-20mV will be used.?
You will require a very stable OPA etc to maintain a +/-20mV Vout for a 0V to +2.5Vin.
E
It's in continuation with our earlier discussion in order to be offsetting a wheat stone bridge. I'll swing the output of the wheat stone bridge which will later be amplified and filtered through a sallen key filter
 

ericgibbs

Joined Jan 29, 2010
18,766
hi ff,
OK,
Do you have a basic sketch you could post showing how the project is intended to work with a bridge.
It sound a doubtful method, perhaps a circuit would give a clearer idea.
E
 

Thread Starter

fieryfire

Joined Feb 14, 2017
150
Hi Eric,

I wanted to do something like this. But i have an input DAC which swings from 0 to 2.5V. But need the output of the bridge to swing from -20mv to 20mv.

I was planning to first shift the level from 0->2.5V to -1.25V to +1.25V and then modify the circuit below to output from -20mV to +20mV. But this would involve making two stages of op amp. but i was wondering if it could be done in a single stage. P.S i dont mind using two stages, but i was wondering that a single stage could be a cheaper.

1582706631977.png
 

ericgibbs

Joined Jan 29, 2010
18,766
Morning ff,
You need to apply a positive offset voltage to the input of U1 OPA in order to swing O1 below zero volts with a 0v thru +2.5v input.
Post your LTS asc file, lets see what we can do with it.
E
 

ericgibbs

Joined Jan 29, 2010
18,766
hi ff,
When you are using a Wheatstone bridge excited by a single supply voltage, you must consider that the bridge Vout will have a steady state of Vext/2.
So the following IA amplifier will have a steady state input on its NI and INV pins [ no bridge signal output ] of Vext/2

This is why the circuit requires the input positive offset voltage on the NI input of the OPA, so that Vout will swing above and below Vext/2.

E

The Yahoo LTSpice user Group has lots of information.
 

Thread Starter

fieryfire

Joined Feb 14, 2017
150
hi ff,
When you are using a Wheatstone bridge excited by a single supply voltage, you must consider that the bridge Vout will have a steady state of Vext/2.
So the following IA amplifier will have a steady state input on its NI and INV pins [ no bridge signal output ] of Vext/2

This is why the circuit requires the input positive offset voltage on the NI input of the OPA, so that Vout will swing above and below Vext/2.

E

The Yahoo LTSpice user Group has lots of information.
Yes this is correct. Since the 0 level(or balanced state of the bridge ) at 2.5V reference voltage is at 1.25V So inorder to go higher or low than the 0 level. we induce - or + voltage to the circuit. This i get . thank you.

But my question is how did you design the preceding circuit(to induce the -20 to +20mV) offset. I havent been able to figure it out completely behind this magic. All the other parts of the circuit i get
1582717861704.png
 
Top