I set up ADC12J1600 using HSDC pro as per this thread: https://e2e.ti.com/support/data-converters/f/73/t/731953
- Initially, I tried a 2MHz single ended tone with 600Mvpp swing and got severe attenuation in the FFT plot (Fundamental = -70dBFs).
- Next, I bypassed the onboard BalUn and provided differential inputs with a 450mVpp swing on each at a 1.225V common mode. (ac coupling caps C1 and C6 intact). The output still remained the same.
- Finally, I removed the ac-coupling capacitors(C1 and C6) and shorted the traces to provide a dc coupled inputs of 300mVpp swing at 1.225V common mode. The FFT still shows -61dBFs for the fundamental
- An observation was that, when the swing is 100mVpp and the VCMi = 150mV, at 7MHz, the FFT shows ~-49dBFs for the fundamental. The FFT spectrum is shown here
- The codes show 16340(saturating input).
Is there a way to differentiate ac coupled vs dc-coupled inputs from the ADC point of view? Is there something I am doing wrong? Please help. The max frequency content of my signal will be 5-7MHz.