ADCV08832CIM National Semiconductor, ADCV08832CIM Datasheet - Page 11

• Manufacturer Part Number: ADCV08832CIM
• Description: Low Voltage/ 8-Bit Serial I/O CMOS A/D Converter with Sample/Hold Function
• Manufacturer: National Semiconductor

Functional Description
digitally analyze the frequency components of the signal.
Depending on the application, further digital processing can
be applied.
6.1 Sampling Rate
The Sampling Rate, sometimes referred to as the Through-
put Rate, is the time between repetitive samples by an
Analog-to-Digital Converter. The sampling rate includes the
conversion time, as well as other factors such a MUX setup
time, acquisition time, and interfacing time delays. Typically,
the sampling rate is specified in the number of samples
taken per second, at the maximum analog-to-digital con-
verter clock frequency.
Signals with frequencies exceeding the Nyquist frequency
(1/2 the sampling rate), will be aliased into frequencies be-
low the Nyquist frequency. To prevent signal degradation,
sample at twice (or more) than the highest frequency com-
ponent of the input signal and/or use of a low pass
(anti-aliasing) filter on the front-end. Sampling at a much
higher rate than the input signal will reduce the requirements
of the anti-aliasing filter.
6.2 Signal-to-Noise Ratio
Signal-to-Noise Ratio (SNR) is the ratio of RMS magnitude
of the fundamental to the RMS sum of all the
non-fundamental signal, excluding the harmonics, up to 1/2
of the sampling frequency (Nyquist).
6.3 Total Harmonic Distortion
Total Harmonic distortion is the ratio of the RMS sum of the
amplitude of the harmonics to the fundamental input fre-
quency.
Where V
V
Applications
2
THD = 20 log [(V
,V
3
, V
4
1
, V
is the RMS amplitude of the fundamental and
5
, V
6
are the RMS amplitudes of the individual
2
2
+ V
3
2
+ V
4
2
+ V
5
2
+ V
(Continued)
6
2
)
1/2
/V
1
]
Protecting the Input
11
harmonics. In theory, all harmonics are included in THD
calculations, but in practice only about the first 6 make
significant contributions and require measurement.
6.4 Signal-to-Noise and Distortion
Signal-to-Noise And Distortion ratio (SINAD) is the ratio of
RMS magnitude of the fundamental to the RMS sum of all
the non-fundamental signals, including the noise and har-
monics, up to 1/2 of the sampling frequency (Nyquist), ex-
cluding DC.
SINAD is also dependent on the number of quantization
levels in the A/D Converter used in the waveform sampling
process. The more quantization levels, the smaller the quan-
tization noise and theoretical noise performance. The theo-
retical SINAD for a n-Bit Analog-to-Digital Converter is given
by:
Thus, for an 8-bit converter, the ideal SINAD = 49.92 dB
6.5 Effective Number of Bits
Effective Number Of Bits (ENOB) is another specification to
quantify dynamic performance. The equation for ENOB is
given by:
Like SINAD, the Effective Number Of Bits combines the
cumulative effect of several errors, including quantization,
ADC non-linearities, noise, and distortion.
6.6 Spurious Free Dynamic Range
Spurious Free Dynamic Range (SFDR) is the ratio of the
signal amplitude to the amplitude of the highest harmonic or
spurious noise component. If the amplitude is at full scale,
the specification is simply the reciprocal of the peak har-
monic or spurious noise.
SINAD = (6.02 n + 1.76) dB
ENOB = [(SINAD - 1.76) / 6.02]
DS200084-9
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