AD7938 Analog Devices, AD7938 Datasheet - Page 13

• Manufacturer Part Number: AD7938
• Description: 8-Channel, 1.5 MSPS, 12-Bit Parallel ADCs with a Sequencer
• Manufacturer: Analog Devices

Specifications of AD7938

• Resolution (bits): 12bit
• # Chan: 8
• Sample Rate: 1.5MSPS
• Interface: Byte,Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: (2Vref) p-p,5V p-p,Uni (Vref),Uni (Vref) x 2,Uni 2.5V,Uni 5.0V
• Adc Architecture: SAR
• Pkg Type: CSP,QFP

Data Sheet
TERMINOLOGY
Integral Nonlinearity
This 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
This 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).
Offset Error Match
This is the difference in offset error between any two channels.
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.
Gain Error Match
This is the difference in gain error between any two channels.
Zero-Code Error
This applies when using the twos complement output coding
option, in particular to the 2 × V
+V
midscale transition (all 0s to all 1s) from the ideal V
(that is, V
Zero-Code Error Match
This is the difference in zero-code error between any two
channels.
Positive Gain Error
This applies when using the twos complement output coding
option, in particular to the 2 × V
+V
code transition (011…110) to (011…111) from the ideal (that
is, V
Positive Gain Error Match
This is the difference in positive gain error between any two
channels.
REF
REF
REF
biased about the V
biased about the V
− 1 LSB) after the zero-code error has been adjusted out.
REF
).
REFIN
REFIN
point. It is the deviation of the
point. It is the deviation of the last
REF
REF
input range with −V
input range with −V
REF
− 1 LSB) after the offset
IN
voltage
REF
REF
to
to
Rev. C | Page 13 of 36
Negative Gain Error
This applies when using the twos complement output coding
option, in particular to the 2 × V
+V
code transition (100…000) to (100…001) from the ideal (that is,
−V
Negative Gain Error Match
This is the difference in negative gain error between any two
channels.
Channel-to-Channel Isolation
Channel-to-channel isolation is a measure of the level of
crosstalk between channels. It is measured by applying a full-
scale sine wave signal to all seven nonselected input channels
and applying a 50 kHz signal to the selected channel. The
channel-to-channel isolation is defined as the ratio of the power
of the 50 kHz signal on the selected channel to the power of the
noise signal on the unselected channels that appears in the FFT
of this channel. The noise frequency on the unselected channels
varies from 40 kHz to 740 kHz. The noise amplitude is at 2 × V
while the signal amplitude is at 1 × V
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 noise varies from 1 kHz to 1 MHz.
where:
Pf is the power at frequency f in the ADC output.
Pf
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
frequency, f
where:
Pf is the power at frequency f in the ADC output.
Pf
S
S
REF
REFIN
is the power at frequency f
is the power at frequency f
PSRR (dB) = 10 log(Pf/Pf
CMRR (dB) = 10 log(Pf/Pf
biased about the V
+ 1 LSB) after the zero-code error has been adjusted out.
S
.
DD
supply of frequency, f
REF
point. It is the deviation of the first
S
S
S
)
in the ADC output.
in the ADC output.
S
)
REF
input range with −V
REF
AD7938/AD7939
. See Figure 5.
IN+
and V
S
. The frequency
IN−
of
REF
to
REF
,