Unipolar to Bipolar OpAmp

Dukel

Other Parts Discussed in Thread: OPA171, OPA191, OPA170, OPA704

Hi,

I would like to amplify a Unipolar 0 - 4.096V to a Bipolar ±10V signal.

I tried filtering the amplifiers, but there is no option to choose input/ouput ranges. Can someone help me?
The signal is coming from a DAC 12-bit

Best regards,

Luc

over 8 years ago

0 Will Wang47 over 8 years ago

TI__Expert 8920 points

Hi Luc,

Your input signal is 4.096V and your output range is 20V, so the gain should be 20/4.096;

The output is bipolar ±10V signal, a high voltage amplifier is needed.

I design with the OPA171, and use the following circuit.

You could also choose the OPA170/2, and if you need higher accuracy, OPA191/2/6/7 may work.

For detailed design information, please refer to the below application note.

http://www.ti.com/lit/an/sboa263/sboa263.pdf

single_to_bipolar.TSC

0 Will Wang47 over 8 years ago in reply to Will Wang47

TI__Expert 8920 points

Sorry to put the wrong reference document, the right document should be the below one:
www.ti.com/.../sboa262.pdf

0 Dukel over 8 years ago in reply to Will Wang47

Intellectual 610 points

Thank you Will Wang,

I did some digging myself and came across the OPA704 wich is included in Tina. I build a circuit that gives the wanted ±10 output. Please take a look

Best regards

0 Will Wang47 over 8 years ago in reply to Dukel

TI__Expert 8920 points

Hi Luc,

I did the simulation, and it looks the output range is -10V to 10.48V. If this is OK for your application, then this circuit is OK.

Regards,

Will

0 Dukel over 8 years ago in reply to Will Wang47

Intellectual 610 points

Dear will,

I also calculated the resistors for your schematic, but I have as small question.

My answers are: 4R3 = R4 and 41.6667R1 = R2

How do you choose the values for the resistors if you get such weird results( at least for R1) do you just pick a resistor that is around 42 times as big or is there something else that makes this easier?

Best regards

0 Will Wang47 over 8 years ago in reply to Dukel

TI__Expert 8920 points

Hi Luc,

I did the resistor value selection work using the "Analog Engineer's Calculator". Below is the software download link.

http://www.ti.com/tool/analog-engineer-calc?keyMatch=analog%20calculator&tisearch=Search--Everything

I use the calculator: Amplifier and Comparators -> Find Amplifier Gain. For we have already know the gain we want, we select the inverting gain circuit to calculate resistor value. For inverting circuit, the gain should be -41.6667, and we choose 1% resistor, it's most common and you could choose more accurate resistor which give you more better match but also cost more. Then we get the result, the below picture show the result.

Highly recommend this tool for you.

Regards,

Will

0 Dukel over 8 years ago in reply to Will Wang47

Intellectual 610 points

Hi Will, do you know how I can reduce the reference noise. I searched the internet and found a solution to use like 4 reference ICs and combine them to set a 10V input with a voltage divider to 2.5v but in the comments this was not a good solution.

0 Will Wang47 over 8 years ago in reply to Dukel

TI__Expert 8920 points

Hi Luc,

You could add caps(value should follow the datasheet instruction) to filter output noise of the reference IC. And you could also add caps parallel with R7 and R2 to get low pass filter to limit the output noise of the total circuit output noise.

Regards,

Will

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Unipolar to Bipolar OpAmp