Actel Fusion Mixed-Signal FPGAs
Ideal Output
Actual Output
0...01
0...00
Offset Error = 1.5 LSB
Input Voltage to Prescaler
Figure 2-87 • Offset Error
Resolution
ADC resolution is the number of bits used to represent an analog input signal. To more accurately
replicate the analog signal, resolution needs to be increased.
Sampling Rate
Sampling rate or sample frequency, specified in samples per second (sps), is the rate at which an
ADC acquires (samples) the analog input.
SNR – Signal-to-Noise Ratio
SNR is the ratio of the amplitude of the desired signal to the amplitude of the noise signals at a
given point in time. For a waveform perfectly reconstructed from digital samples, the theoretical
maximum SNR (EQ 2-21) is the ratio of the full-scale analog input (RMS value) to the RMS
quantization error (residual error). The ideal, theoretical minimum ADC noise is caused by
quantization error only and results directly from the ADC’s resolution (N bits):
SNRdB[MAX] = 6.02dB × N + 1.76dB
EQ 2-21
SINAD – Signal-to-Noise and Distortion
SINAD is the ratio of the rms amplitude to the mean value of the root-sum-square of the all other
spectral components, including harmonics, but excluding DC. SINAD is a good indication of the
overall dynamic performance of an ADC because it includes all components which make up noise
and distortion.
Total Harmonic Distortion
THD measures the distortion content of a signal, and is specified in decibels relative to the carrier
(dBc). THD is the ratio of the RMS sum of the selected harmonics of the input signal to the
fundamental itself. Only harmonics within the Nyquist limit are included in the measurement.
TUE – Total Unadjusted Error
Preliminary v1.7
2-113
ACTEL [ Actel Corporation ]
