Hi,

   Maybe I can ask the question in another way, is it possible to converter the singled-ended input signal to differential output signals from the architecture shown below?

Hi,


If you treat the single-ended input as a common-mode + differential signal, then you just want to reject the common-mode part. So i guess you want to make sure the amplifier has very good common-mode rejection.

Also, you should check the common-mode output impedance. If it is high compared to those resistor values, then the effectiveness might depend on the loading to the op-amp.


just my thoughts...
Aaron

Hi Jacki,


I'm not sure if you understood my meaning. If you cancel the common-mode signal, all you will have left is a differential-mode signal. i.e. you will get perfect single-ended to differential conversion. That's in an ideal world however.

I had a look at the datasheet, and to me its not obvious what kind of common-mode cancellation you will get. Maybe somebody else can shed some light. If I had to guess, I would say that there are 2 factors you need to take into account.

1. The common-mode gain.
For the common-mode gain, I think it is a resistive divider between output impedance of the device, and (RFP + RFG). So at 1 MHz it would be 20/20020 = -60 dB.

2. The output balance error.
At 1 MHz its -40 dB. I assume that it means that if you provide a perfect differential signal, how much is converted to common-mode at the output.

In this case, -40 dB is much worse than -60 dB, so you can just look at the output balance error. Remember that it is frequency dependent.


regards,
Aaron

Sheldon,


this wasn't actually my question, but perhaps you care to elaborate?

Quote:


I read the product description (and skimmed through the data sheet) and it says that it is suitable for single-to-differential conversion, but I wasn't able to identify which parameter describes the single-ended to differential performance. What have you seen that I didn't?

Quote:


Common-mode gain normally means common-mode input to differential output conversion gain, but what I was referring to was common-mode input to common-mode output gain. The simple calculation I included should have made that obvious.

I realise I used the wrong terminology, but honestly, the way I was using it makes more sense, and the normal meaning should be called common-mode to differential gain or something like that. Whatever the case, the datasheet doesn't say anything about common-mode input to common-mode output gain.

Is this the confusion you were talking about?


Aaron