A simulation is shown:

(8-bit, 17 periods, nonlinearity sine amplitude 0.005, 1 period)

The lowest frequency shows the DC content.

The signal at frequency 17 has -9 dB magnitude.

The first harmonic at frequency 34 has -55.15 dB magnitude.

The average noise level is -82 dB giving a total noise of -59 dB (without Harmonic of -58 dB).

ADC characteristic can be determine:

Signal to noise ratio: | SNR = -9.06 dB - (- 59 dB) = 50 dB.
Signal magnitude line 1 and total noise magnitude line 2.
From there on total noise magnitude remains constant. No more harmonics. |

Signal to distortion ratio: | SDR = -9.06 dB - (-55.15 dB) = 46.09 dB
Signal magnitude line 1 and signal magnitude line 2. |

Signal to noise and distortion ratio: | SNDR = - 9.06 dB - (- 53.66 dB) = 44.6 dB
line 1 |

Spurious free dynamic range: | SFDR = -9.06 dB - (- 55.15 dB) = 46.09 dB
Signal magnitude line 1 and signal magnitude line 2. |

Since there is only one harmonic SDR and SFDR is the same.

Signal to distortion ratio (SDR): signal to total distortion power (all harmonics).

\( SDR = 10 \cdot \log \left( \frac{Signal \; power}{Total \; distortion \; power}\right) \)

Signal to distortion ratio (SNDR): signal to noise and distortion power.

\( SNDR = 10 \cdot \log \left( \frac{Signal \; power}{Noise \; and \; distortion \; power}\right) \)

Spurious free dynamic range (SFDR): signal to highest harmonic.

\( SFDR = 10 \cdot \log \left( \frac{Signal \; power}{Largest \; harmonic \; power}\right) \)

The objective should be to have all numbers the same getting the expected ENOB.

Harmonics should be eliminated correcting non linearities.

Harmonics can also be eliminated, if the power supply during conversion is not stable.

Non harmonic peaks can come from the power supply or radio interference.

The total noise without harmonics can be increaed due to device parameters: high resistors,
low capacitance values, high transistor or operational amplifier input noise.

Diagnosis tries to determine the exact root cause for errors to guide the circuit designer
to a better design.

Unfortunately there is little literature available about diagnosis strategies.