Hi
I have a project where I use a ADS131M02 AD converter together with an input ”amplifier” that actually is not an amplifier but a signal conditioning circuit.
The input is a tone signal in the range +10dBm to -60dBm (impedance is 600 ohm, measurement unit is dB milliwatt).
The sampling frequency of the AD converter is 8kHz and the input frequency is 600 Hz to 2300 Hz.
When the input frequency is 650 Hz, everything works fine, the output correspond to the input signal.
But when the input is above 1500 Hz, the output is too low.
At 2300 Hz the output from the AD converter is app. one half of the input signal.
Do You have a good explanation of this – we have not been able to figure it out.
We think that it should be possible to convert a 2350Hz using an 8kHz sampling frequency and getting the right amplitude.
When we make an FFT of the input signal, the frequency is correct, the amplitude is not.
The software setup of the AD converter is not changed, only the sampling frequency is setup.
The rest of the values are default values.
See also the attached file regarding input / AD output values.
