Hi ADI,

I short EVB AD7176-2 input pin with GND to get ENOB=19.8bit, according to MT-003, SINAD = 6.02*ENOB+1.76dB = 120dB.

And CN0310 shows AD7176-2 can measure SINAD 99.9dB.

I use APx515 to transmit pure 1kHz sinewave to test AD7176-2 RX quality, and use the raw data which get from AD7176-2 to calculate THD+N via MATLAB FFT, I can only get SINAD 75dB.

The result is really confused me.

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1. Because I can't find the FFT tool on AD717x Eval+ Software,

could you teach me how you get the FFT as above figure 6?

2. The attachment is raw data, might you use the tool to help me check it?

Thanks a lot.

Homeway

Hi Homeway,

ENOB is a measurement of the resolution with a sine wave input. It is a function of SINAD for a certain frequency. Thus, having the input connected to ground will not give you the exact value of ENOB in 1kHz signal. On the other hand, SINAD is the ratio of the rms value of the signal to the rms value of all spectral components including harmonics but except DC.

The difference of your result, the 75dB, the actual SINAD, 99.9dB, can be caused by different input amplitude. The actual SINAD was measured at -6dBFs or 2.5Vpp input with 5V reference. The setup can also cause noise that can lower the measured SINAD. For this, can you show your current setup.

Thanks,

Daryl