AD7357 Analog Devices, AD7357 Datasheet - Page 10

• Manufacturer Part Number: AD7357
• Description: Differential Input, Dual, Simultaneous Sampling, 4.25 MSPS, 14-Bit, SAR ADC
• Manufacturer: Analog Devices

Specifications of AD7357

• Resolution (bits): 14bit
• # Chan: 2
• Sample Rate: 4.25MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Bip,Diff-Uni,Usr-Defined Range/Offset
• Ain Range: Vcm ± Vref/2
• Adc Architecture: SAR
• Pkg Type: SOP

TERMINOLOGY
Integral Nonlinearity (INL)
INL is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. 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.
Negative Full-Scale Error
Negative full-scale error is the deviation of the first code transi-
tion (00 … 000) to (00 … 001) from the ideal (that is, −V
0.5 LSB) after the midscale error has been adjusted out.
Negative Full-Scale Error Match
Negative full-scale error match is the difference in negative full-
scale error between the two ADCs.
Midscale Error
Midscale error is the deviation of the midscale code transition
(011 … 111) to (100 … 000) from the ideal (that is, 0 V).
Midscale Error Match
Midscale error match is the difference in midscale error
between the two ADCs.
Positive Full-Scale Error
Positive full-scale error is the deviation of the last code transi-
tion (111 … 110) to (111 … 111) from the ideal (that is, V
1.5 LSB) after the midscale error has been adjusted out.
Positive Full-Scale Error Match
Positive full-scale error match is the difference in positive full-
scale error between the two ADCs.
ADC-to-ADC Isolation
ADC-to-ADC isolation is a measure of the level of crosstalk
between ADC A and ADC B. It is measured by applying a full-
scale 1 MHz sine wave signal to one of the two ADCs and
applying a full-scale signal of variable frequency to the other
ADC. The ADC-to-ADC isolation is defined as the ratio of the
power of the 1 MHz signal on the converted ADC to the power
of the noise signal on the other ADC that appears in the FFT.
The noise frequency on the unselected channel varies from
100 kHz to 2.5 MHz.
Power Supply Rejection Ratio (PSRR)
PSRR is defined as 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
of the input varies from 5 kHz to 25 MHz.
where:
Pf is the power at frequency, f, in the ADC output.
Pf
AD7357
S
is the power at frequency, f
PSRR (dB) = 10 log(Pf/Pf
DD
supply of the frequency, f
S
S
)
, in the ADC output.
S
. The frequency
REF
REF
+
Rev. B | Page 10 of 20
−
Common-Mode Rejection Ratio (CMRR)
CMRR is defined as 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 common-mode voltage of V
of frequency, f
where:
Pf is the power at frequency, f, in the ADC output.
Pf
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 ±1 LSB, after the end of conversion.
Signal-to-(Noise + Distortion) Ratio (SINAD)
SINAD 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 SINAD for an ideal N-bit converter with a sine
wave input is given by
Thus, for a 12-bit converter, SINAD is 74 dB and for a 14-bit
converter, SINAD is 86 dB.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the funda-
mental. For the AD7357, it is defined as
where:
V
V
through the sixth harmonics.
Peak Harmonic or Spurious Noise
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
the fundamental. Normally, the value of this specification 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.
1
2
S
, V
is the rms amplitude of the fundamental.
is the power at frequency, f
CMRR (dB) = 10log (Pf/Pf
SINAD = (6.02 N + 1.76) dB
THD
3
, V
4
, V
( )
dB
5
, and V
S
, as follows:
=
−
S
/2 and excluding dc) to the rms value of
20
6
are the rms amplitudes of the second
log
V
2
2
S
, in the ADC output.
S
+
)
S
V
/2), excluding dc. The ratio is
3
2
+
V
V
1
4
2
+
V
5
IN+
2
+
and V
V
6
2
IN−