Hi,
We have need to use the differential input mode, however, when we do so we are seeing additional harmonics in the resulting data stream.
To test this we have AC terminated the input pins to ground via a 27nF capacitor (although we are getting the same results when we short the differential inputs together).
We are not using the AGC and the digital ADC gains are set to 0. The PGA gain is also set to 0.
In SE mode with the analog selection being to pin IN1L and IN1R i.e.
reg[52] = 0b11110011
reg[54] = 0b01111111
reg[55] = 0b11110011
reg[57] = 0b01111111
The following spectrum is achieved (each color being a different channel, L and R over 3 chips synchronously clocked).
Conversely when switching to differential inputs IN2L(P) - IN3L(M) and IN2R(P) - IN3R(M) i.e.
reg[52] = 0b00111111
reg[54] = 0b01111111
reg[55] = 0b00111111
reg[57] = 0b01111111
the following spectrum was found
The differential signal display less white noise, and no more slow-time drift, however, we are now also seeing the harmonic like components which are not present in the SE data.
Is this normal, or is there something wrong in our configuration? If so do you have any idea what might cause it?
