# What matters, the rms or peak value of the Analog signal to choose appropriate ADC for digitization?

i have an 23 bit ADC with voltage reference of 1.4 V. If my input Analog signal is AC with frequency 50 HZ and its rms ranges from 0.2 Vrms to 1.3 Vrms. Then its peak voltages will vary from 0.28 V to 1.838 V.

Now, considering ADC high value that it can digitize (1.4 V). What does it mean? I mean, if i consider input Analog rms values or peak values to find out that this adc will work for my inputs. Because if i consider rms value then it probably would work, but it ADC is concerned with max peak of incoming Analog signal then my inputs with peaks higher than 1.4 V won't be able to digitized correctly.?

Please guide, what is considered by choosing ADC, is it the rms of Analog or peak.?

And if it is peak, then what would happen if Analog value is higher than adc specified value? Will all values higher than 1.4 V will treated as same digital value??

• What type of ADC do you have and what is the AC input relative to ground? In means that it goes + and -1.8Vpk. Commented Sep 11, 2018 at 12:04
• Peak of course. Commented Sep 11, 2018 at 12:07
• Do you want to measure the waveform (i.e. so you can see the 50Hz sine wave) or just the amplitude at say 1Hz? Either way, you're going to need a different ADC and/or some signal conditioning. Commented Sep 11, 2018 at 12:10
• I want to know that at peak of input signal (when signal value s highest in cycle) is 1.8V. Will it be converted into a valid digital value by this ADC?? Commented Sep 11, 2018 at 12:21
• Will all values higher than 1.4 V will treated as same digital value?? Maybe, maybe not. The data sheet should be explicit about what happens in those circumstances. These days, most ADCs seem to be well behaved and limit at the maximum code, some even have an overflow bit. Commented Sep 11, 2018 at 14:00

An RMS sine wave of 1.3 volts has a peak-to-peak value of 2 x $\sqrt2$ x 1.3 volts i.e. 3.677 volts p-p. It is not only that range that has to be accommodated by your ADC but you also need to DC bias the AC signal so that when it is 0 volts AC, the DC level is 3.677 volts / 2 i.e. 1.838 volts.