AD7478A Analog Devices, AD7478A Datasheet - Page 14

• Manufacturer Part Number: AD7478A
• Description: 8-Bit, 1 MSPS, Low-Power A/D Converter in SC70 and MSOP Packages
• Manufacturer: Analog Devices

Specifications of AD7478A

• Resolution (bits): 8bit
• # Chan: 1
• Sample Rate: 1.2MSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni Vdd
• Adc Architecture: SAR
• Pkg Type: SC70,SOP

AD7476A/AD7477A/AD7478A
TERMINOLOGY
Integral Nonlinearity (INL)
INL is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. For the
AD7476A/AD7477A/AD7478A, the endpoints of the transfer
function are zero scale (1 LSB below the first code transition),
and full scale (1 LSB above the last code transition).
Differential Nonlinearity (DNL)
DNL is the difference between the measured and the ideal
1 LSB change between any two adjacent codes in the ADC.
Offset Error
This is the deviation of the first code transition (00 . . . 000) to
(00 . . . 001) from the ideal, that is, AGND + 1 LSB.
Gain Error
This is the deviation of the last code transition (111 . . . 110) to
(111 . . . 111) from the ideal, that is, V
error has been adjusted out.
Track-and-Hold Acquisition Time
The track-and-hold amplifier returns to track mode at the end
of a conversion. The track-and-hold acquisition time is the time
required for the output of the track-and-hold amplifier to reach
its final value, within  0.5 LSB, after the end of conversion. See
the Serial Interface section for more details.
Signal-to-(Noise + Distortion) Ratio (SINAD)
This is the measured ratio of signal-to-(noise + distortion) at
the output of the ADC. The signal is the rms amplitude of the
fundamental. Noise is the sum of all nonfundamental signals up
to half the sampling frequency (f
dependent on the number of quantization levels in the digitiza-
tion process; the more levels, the smaller the quantization noise.
The theoretical signal-to-(noise + distortion) ratio for an ideal
N-bit converter with a sine wave input is given by signal-to-
(noise + distortion) = (6.02 N + 1.76) dB. Thus, it is 74 dB for a
12-bit converter, 62 dB for a 10-bit converter, and 50 dB for an
8-bit converter.
Total Unadjusted Error (TUE)
This is a comprehensive specification that includes the gain,
linearity, and offset errors.
S
/2), excluding dc. The ratio is
REF
– 1 LSB after the offset
Rev. F | Page 14 of 28
Total Harmonic Distortion (THD)
Total harmonic distortion is the ratio of the rms sum of
harmonics to the fundamental. It is defined as
where V
V
sixth harmonics.
Peak Harmonic or Spurious Noise (SFDR)
Peak harmonic or spurious noise is defined as the ratio of the rms
value of the next largest component in the ADC output spectrum
(up to f
Normally, the value of this specification is determined by the largest
harmonic in the spectrum. For ADCs where the harmonics are
buried in the noise floor, it is a noise peak.
Intermodulation Distortion (IMD)
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities create distortion
products at sum and difference frequencies of mfa,  n fb, where
m and n = 0, 1, 2, 3, and so on. Intermodulation distortion
terms are those for which neither m nor n are equal to zero. For
example, the second-order terms include (fa + fb) and (fa – fb),
and the third-order terms include (2fa + fb), (2fa – fb), (fa + 2fb),
and (fa – 2fb).
The AD7476A/AD7477A/AD7478A are tested using the CCIF
standard where two input frequencies are used (see fa and fb in
the Specifications section). In this case, the second-order terms
are usually distanced in frequency from the original sine waves,
while the third-order terms are usually at a frequency close to the
input frequencies. As a result, the second- and third-order terms
are specified separately. The calculation of the intermodulation
distortion is per the THD specification, where it is the ratio of
the rms sum of the individual distortion products to the rms
amplitude of the sum of the fundamentals expressed in decibels.
4
, V
THD
5
, and V
S
/2 and excluding dc) to the rms value of the fundamental.
1
is the rms amplitude of the fundamental, and V
(
dB
6
)
are the rms amplitudes of the second through the
=
20
log
V
2
2
+
V
3
2
+
V
V
1
4
2
+
V
5
2
+
V
6
2
2
, V
3
,