THS4131: Single to Differential Conversion for transferring the signals through a ribbon cable assembly prone to noise and then converting back to Single Ended.

Hello Nidhin,

  Thank you for providing a system block diagram; it was very helpful to visualize the setup and question. 

  Fortunately, there are a lot of options, you can either use a regular operational amplifier as a difference amplifier or you can use a dedicated instrumentational amplifier which is dedicated to differential to single-ended with an emphasis on high DC performance (CMRR) if that is an important factor for your design. Here is a thread that shows these two choices: https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/593129/differential-signalling-to-single-ended-adc?tisearch=e2e-sitesearch&keymatch=INA826S

  But, in your case you do not really need the high input impedance. 

 I am assuming your voltage supplies are in the 5V range based on the THS4131 choice, but if that is not the case, let us know what your desired voltage supplies are for the new board and that will help narrow down to a more suitable choice for your design especially around if the amplifier needs to be RRIO (rail-to-rail input/output range). 

 On our end for high speed amplifier group (>50MHz) which this thread is linked under, I would recommend either the OPA891 which is our very low noise and THD device or OPA365 which is overall good DC and AC part that is RRIO. 

  If you want to go to higher DC precision part that is <50MHz, or want a instrumentational amplifier (INA) recommendation, I could redirect thread to the precision amplifier group to offer suggestions on this thread.

Thank you,

Sima  

Thankyou Sima for the detailed answer,

The single ended signal is .3V to 3.5V varying at maximum 4 MHz

Available voltage at the capture board is 4V in one variant and 5V in another variant.  I could not find reference circuit for THS4131 on PSpice for TI, Right clicking on the symbol does not show reference design ? am I missing something here ?

On the main board also available minimum voltage is 4V but in worst case we can manage 5V as well.

Our aim is to get rid of the noise that we are currently getting with the single ended signal. You can also give some options which i will explore and decide.

Hello Nidhin,

  With your signal range and 4-5V supply requirement, I would recommend using the OPA365 as a standard differenced/differential amplifier would work. The supply voltage range of the OPA365 is from 2.2V to 5.5V and it is RRIO amplifier which means it can accept input signals and output signals very close to the supply rails of the amplifier. Here is the output range of the device:

Simulation circuits for our devices can be found on the product folder under Design & Development --> Design tools & simulation. It looks like this device does not a reference circuit, just the model. You may use the THS4531A reference circuit as an example and replace the THS4531A with the THS4131. Let me know if you are unable to get this method to work. 

Thank you,

Sima

Thanks Sima,

That work around helped.

I was able to simulate both amplifiers connected in cascaded. I think THS4131 is not performing well close to 3.5 Volt at the input.

Could you suggest another Part ? I think a rail to rail part would be more good.

Red Input Single ended signal

And Green is output single ended converted from differential.

File attached

THS4531A.DSN

Hi Sima,

Just wanted to let you know I'm moving forward with THS4521 at the capture board and OPA365 at the New Board.

Hi Sima,

Just an update, when tried with a 4MHZ signal at the input the OPA365 has some attenuation, therefore proceeding with OPA836 instead of OPA365. Please let me know if you have any comment on the final selection. Thankyou

Hello Nidhin,

  Sorry for the delay in response, I was on a work trip then I got sick. Thank you for the updates 

  For the THS4131, its output voltage swing is down to 3.6V, and depending on the load it could have that affect.

  Good choice on THS4521 since it is a rail-to-rail output device, and OPA836 has higher GBW compared to OPA365 while also being rail-to-rail output. I do not see any issues at 4MHz at unity gain:

  I hope it has been working out for you! 

Thank you,

Sima