Hi, Changing the Cbypass from 15 nF to 1 uF or programming LNA_HPF_PROG or RED_LNA_HPF_3X differently doesn't affect at what * input level* the harmonic distortion appears in terms of input voltage (Vpp). Changing Cbypass or HPF programming only affects the sampled level by the ADC. The only way we have found to get rid of the distortion is to completely disable LNA and PGA HPF. If either or both HPF are enabled there are distortion problems. Disabling the HPF is not an option as the resulting DC offset level is too high, will vary between individual chips and temperature. The datasheet talks about setting low cut-off frequencies (< 2 kHz) so to us it seems unreasonable that AFE5818 cannot handle a 30 kHz input signal within the input voltage range properly. That's why we were hoping we have incorrectly programmed the circuit. Please have your system engineer confirm if this is a non-documented hardware issue or how to program the IC correctly to solve the issue. Thank you, Christer
↧