AD7457 Analog Devices, AD7457 Datasheet - Page 10

• Manufacturer Part Number: AD7457
• Description: Pseudo Differential Input, 100 kSPS, 12-Bit ADC in 8-Lead SOT-23
• Manufacturer: Analog Devices

Specifications of AD7457

• Resolution (bits): 12bit
• # Chan: 1
• Sample Rate: 100kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (Vref) p-p
• Adc Architecture: SAR
• Pkg Type: SOT

AD7457
TERMINOLOGY
Signal to (Noise + Distortion) Ratio (SINAD)
The measured ratio of SINAD 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
number of quantization levels in the digitization process; the
more levels, the smaller the quantization noise. The theoretical
SINAD ratio for an ideal N-bit converter with a sine wave input
is given by
Therefore, for a 12-bit converter, the SINAD is 74 dB.
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental. For
the AD7457, it is defined as
where:
V
V
sixth harmonics.
Peak Harmonic or Spurious Noise
The ratio of the rms value of the next largest component in the
ADC output spectrum (up to f
value of the fundamental. Normally, the value of this specifica-
tion is determined by the largest harmonic in the spectrum, but,
for ADCs where the harmonics are buried in the noise floor, it is
a noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities creates distortion prod-
ucts at sum and difference frequencies of mfa ± nfb, where m, 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), while the
third order terms include (2fa + fb), (2fa − fb), (fa + 2fb) and
(fa − 2fb).
The AD7457 is tested using the CCIF standard, where two input
frequencies near the top end of the input bandwidth are used.
In this case, the second order terms are usually distanced in fre-
quency 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.
1
2
, V
is the rms amplitude of the fundamental.
THD
3
Signal
, V
4
, V
( )
dB
to
5
S
, and V
/2), excluding dc. The ratio is dependent on the
(
Noise
=
20
6
log
+
are the rms amplitudes of the second to the
Distortion
V
2
2
+
S
/2 and excluding dc) to the rms
V
3
) (
2
=
+
V
V
. 6
1
4
2
02
+
N
V
5
2
+
+
. 1
V
76
6
2
)
dB
Rev. A | Page 10 of 20
The calculation of the intermodulation distortion is as per the
total harmonic distortion 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 dB.
Aperture Delay
The amount of time from the leading edge of the sampling
clock until the ADC actually takes the sample.
Aperture Jitter
The sample-to-sample variation in the effective point in time at
which the actual sample is taken.
Full-Power Bandwidth
The full-power bandwidth of an ADC is that input frequency
at which the amplitude of the reconstructed fundamental is
reduced by 0.1 dB or 3 dB for a full-scale input.
Integral Nonlinearity (INL)
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function.
Differential Nonlinearity (DNL)
The difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Offset Error
The deviation of the first code transition (000...000 to 000...001)
from the ideal (that is, AGND + 1 LSB).
Gain Error
The deviation of the last code transition (111...110 to 111...111)
from the ideal (that is, V
been adjusted out.
Track-and-Hold Acquisition Time
The minimum time required for the track-and-hold amplifier to
remain in track mode for its output to reach and settle to within
0.5 LSB of the applied input signal.
Power Supply Rejection Ratio (PSRR)
The ratio of the power in the ADC output at full-scale
frequency, f, to the power of a 100 mV p-p sine wave applied to
the ADC V
input varies from 1 kHz to 1 MHz.
Pf is the power at frequency f in the ADC output; Pfs is the
power at frequency fs in the ADC output.
PSRR (dB) = 10 log( Pf/Pfs )
DD
supply of frequency fs. The frequency of this
REF
− 1 LSB), after the offset error has