Is there a way to detect 1ms pulse with voltage of around 300mV?

[KS]

We are already using ADC for battery sense, also tried using ADC and LPCOM but could not get any reliable result.

[Roger Clark]

I'm not sure which response you replied to, as you posted your response and an answer

Using the ADC is not ideal for pulse detection, because of the acquisition time

I don't know the acquisition time of the ADC on the nRF51822 but I'm fairly sure if you ran it constantly, you would be able to detect a 1mS wide pulse.

However normally pulse detection is done using GPIO and possibly via interrupt GPIOTE

Do you require a low power solution, as I don't think an OpAmp is likely to be low power.

What OpAmp did you try using, is it "rail to rail" i.e will it drive the output to the supply voltage ?