# Differential to single ended circuit

I have a differential signal up to 1.5 MHz and have to transform it to a single ended signal.

I have found this amplifier which has a BW of 2.2 MHz and should therefore be okay for this task.

The manufacturer also offers a simulation program, where I've tested this where $R_f = R_g$ and $R_1 = R_2$.

The input signals are 500mV pp and have a common voltage of 1V. Is this the right way of transforming a differential signal to a single-ended one?

• yes, but 2.2MHz is waaaaay too little bandwidth for a 1.5MHz signal, if you look at the distortion graph in the data sheet, they only bother to plot it to 5kHz! 2.2MHz is -3dB. Nov 28, 2017 at 14:13
• I understand. I guess it is normal for instrumentation amplifiers to not have a big BW at all. Nov 28, 2017 at 14:49
• Your opamp hasn't 2,2MHz bandwidth. Its gain-bandwidth product is 2,2MHz. You cannot have much gain at 1,5MHz. If you do not need gain, only conversion from differential to single ended, it can work, but it's still a gamble due missing specs at 1,5MHz. What is the spectral range of your signal? 1,5MHz frequency gives no info about it. There can exist usable other solutions.
– user136077
Nov 28, 2017 at 15:20
• @user287001 my signal ranges from DC to 1.5 MHz and you are right, I do not need gain. Just want to convert it. Nov 28, 2017 at 15:21
• @SpehroPefhany I just read the op-amp section in "the Art of electronics" and it explained alot. What a great book! Nov 28, 2017 at 18:40

It's one right way, assuming that the other characteristics of this circuit are acceptable in your application.

For example, the input impedance is relatively low, compared, say, to an instrumentation amplifier. But if your source impedance is low, it shouldn't be a problem.

It also requires careful resistor matching in order to achieve a high CMRR. But matched resistor networks are readily available, as well as amplifiers that have the resistors integrated right on the chip.

EDIT: My comments above were based solely on looking at the topology of the circuit diagram in your question. However, the amplifier you linked to, the AD8422, actually is an instrumentation amplifier, so that circuit diagram does not apply.

• the inputs are coming from an amplifier output so I guess they are low. Nov 28, 2017 at 14:41

If the performance must be equal from 0 to 1.5MHz, I would try a high frequency differential amplifier IC, for example AD8132. Your current candidate has specs which seem to dive at much lower frequencies than 1.5MHz - for example the max output amplitude is virtually zero at 1MHz. High frequency differential amp ICs are fully usable to several tens of megahertzes, even higher.