AD7721ARZ-REEL Analog Devices Inc, AD7721ARZ-REEL Datasheet - Page 8

• Manufacturer Part Number: AD7721ARZ-REEL
• Description: 16-BIT SIGMA DELTA A-D I.C.
• Manufacturer: Analog Devices Inc

Specifications of AD7721ARZ-REEL

• Number Of Bits: 16
• Sampling Rate (per Second): 468.75k
• Data Interface: Serial, Parallel
• Number Of Converters: 1
• Power Dissipation (max): 150mW
• Voltage Supply Source: Analog and Digital
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (0.300", 7.50mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD7721
TERMINOLOGY
Integral Nonlinearity
This is the maximum deviation of any code from a straight line
passing through the endpoints of the transfer function. The end-
points of the transfer function are zero scale (not to be con-
fused with bipolar zero), a point 0.5 LSB below the first code
transition (100 . . . 00 to 100 . . . 01 in bipolar mode and
000 . . . 00 to 000 . . . 01 in unipolar mode) and full scale, a point
0.5 LSB above the last code transition (011 . . . 10 to 011 . . . 11 in
bipolar mode and 111 . . . 10 to 111 . . . 11 in unipolar mode). The
error is expressed in LSBs.
Differential Nonlinearity
This is the difference between the measured and the ideal 1 LSB
change between two adjacent codes in the ADC.
Common Mode Rejection Ratio
The ability of a device to reject the effect of a voltage applied to
both input terminals simultaneously—often through variation of
a ground level—is specified as a common-mode rejection ratio.
CMRR is the ratio of gain for the differential signal to the gain
for the common-mode signal.
Unipolar Offset Error
Unipolar offset error is the deviation of the first code transition
from the ideal VIN1 voltage which is (VIN2 + 0.5 LSB) when
operating in the unipolar mode.
Bipolar Offset Error
This is the deviation of the midscale transition (111 . . . 11
to 000 . . . 00) from the ideal VIN1 voltage which is (VIN2 –
0.5 LSB) when operating in the bipolar mode.
Unipolar Full-Scale Error
Unipolar full-scale error is the deviation of the last code transition
(111 . . . 10 to 111 . . . 11) from the ideal VIN1 voltage which is
(VIN2 + V
Bipolar Full-Scale Error
The bipolar full-scale error refers to the positive full-scale error and
the negative full-scale error. The positive full-scale error is the
deviation of the last code transition (011 . . . 10 to 011 . . . 11) from
the ideal VIN1 voltage which is (VIN2 + V
The negative full-scale error is the deviation of the first code transi-
tion (100 . . . 00 to 100 . . . 01) from the ideal VIN1 voltage which
is (VIN2 – V
Signal to (Noise + Distortion)
Signal to (Noise + Distortion) is measured signal to noise at the
output of the ADC. The signal is the rms magnitude of the funda-
mental. Noise is the rms sum of all the nonfundamental signals up
to half the sampling frequency (f
ponent. Signal to (Noise + Distortion) is dependent on the num-
ber of quantization levels used in the digitization process; the more
levels, the smaller the quantization noise. The theoretical Signal to
(Noise + Distortion) ratio for a sine wave input is given by
where N is the number of bits. Thus, for an ideal 12-bit converter,
Signal to (Noise + Distortion) = 74 dB.
Total Harmonic Distortion
Total Harmonic Distortion (THD) is the ratio of the rms sum
of harmonics to the rms value of the fundamental. For the
AD7721, THD is defined as
Signal to (Noise + Distortion) = (6.02 N + 1.76) dB
THD
REFIN
REFIN
– 3/2 LSBs).
20 log
/2 + 0.5 LSB).
(V
2
2
CLK
V
/2) but excluding the dc com-
3
2
V
V
1
4
REFIN
2
V
/2 – 3/2 LSB).
5
2
V
6
2
)
–8–
where V
V
sixth harmonic.
USING THE AD7721
ADC Differential Inputs
The AD7721 uses differential inputs to provide common-mode
noise rejection. In the bipolar mode configuration, the analog
input range is
midway between successive integer LSB values. The output
code is 2s complement binary with 1 LSB = 0.61 mV in paral-
lel mode and 38 V in serial mode. The ideal input/output
transfer function is illustrated in Figure 2.
In the unipolar mode, the analog input range is 0 V to 2.5 V.
Again, the designed code transitions occur midway between suc-
cessive integer LSB values. The output code is straight binary with
1 LSB = 0.61 mV in parallel mode and 38 V in serial mode. The
ideal input/output transfer function is shown in Figure 3.
4
, V
Figure 3. AD7721 Unipolar Mode Transfer Function
Figure 2. AD7721 Bipolar Mode Transfer Function
5
111...111
111...110
111...101
111...100
000...011
000...010
000...001
000...000
and V
011...111
011...110
000...010
000...001
000...000
111...111
111...110
100...001
100...000
1
is the rms amplitude of the fundamental and V
OUTPUT
CODE
6
OUTPUT
CODE
are the rms amplitudes of the second through the
–REF IN/2
0V
1.25 V. The designed code transitions occur
DIFFERENTIAL INPUT VOLTAGE (VIN1–VIN2)
AD7721
DIFFERENTIAL INPUT VOLTAGE (VIN1–VIN2)
AD7721
0V
+REF IN/2–1LSB
REF IN–1LSB
2
REV. A
, V
3
,