AD7896BR Analog Devices Inc, AD7896BR Datasheet - Page 6

• Manufacturer Part Number: AD7896BR
• Description: A/D Converter (A-D) IC
• Manufacturer: Analog Devices Inc

Specifications of AD7896BR

• Package/case: 8-SOIC
• Features: +2.7V To 5V, 12?Bit ADC In 8?Pin
• Interface Type: Serial
• Leaded Process Compatible: No
• Number Of Bits: 12
• Number Of Channels: 1
• Peak Reflow Compatible (260 C): No
• Rohs Status: RoHS non-compliant
• Sampling Rate (per Second): 100k
• Data Interface: Serial
• Number Of Converters: 1
• Power Dissipation (max): 10.8mW
• Voltage Supply Source: Single Supply
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With: EVAL-AD7896CBZ - BOARD EVALUATION FOR AD7896CBZ
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

AD7896
TERMINOLOGY
Relative Accuracy
This is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function. The end-
points of the transfer function are zero scale (which is V
AGND + 1/2 LSB), a point 1/2 LSB below the first code transi-
tion (00 . . . 000 to 00 . . . 001), and full scale (which is V
AGND + V
transition (11 . . . 110 to 11 . . . 111).
Differential Nonlinearity
This is the difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Unipolar Offset Error
This is the deviation of the first code transition (00 . . . 000 to
00 . . . 001) from the ideal V
Positive Full-Scale Error
This is the deviation of the last code transition (11 . . . 110 to
11 . . . 111) from the ideal (V
after the offset error has been adjusted out.
Track-and-Hold Acquisition Time
Track-and-hold acquisition time is the time required for the
output of the track-and-hold amplifier to reach its final value,
within ± 1/2 LSB, after the end of conversion (the point at which
the track-and-hold returns into track mode). It also applies to a
situation where there is a step input change on the input voltage
applied to the selected V
the user must wait for the duration of the track-and-hold acquisi-
tion time after the end of conversion or after a step input change
to V
operates to specification.
Signal-to-(Noise + Distortion) Ratio
This is the measured ratio of signal-to-(noise + distortion) at the
output of the ADC. The signal is the rms amplitude of the fun-
damental. 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:
Thus, for a 12-bit converter, this is 74 dB.
IN
before starting another conversion, to ensure the part
Signal-to-(Noise + Distortion) = (6.02N + 1.76) dB
DD
– 1/2 LSB), a point 1/2 LSB above the last code
IN
input of the AD7896. It means that
IN
S
IN
/2), excluding dc. The ratio is
voltage (AGND + 1 LSB).
= AGND + V
DD
– 1 LSB)
IN
IN
=
=
–6–
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the rms sum of
harmonics to the fundamental. For the AD7896, it is defined as:
where V
V
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
fundamental. Normally, the value of this specification is deter-
mined by the largest harmonic in the spectrum, but for parts
where the harmonics are buried in the noise floor, it will be a
noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities will create distortion
products at sum and difference frequencies of mfa ± nfb where
m, n = 0, 1, 2, 3, etc. 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 AD7896 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 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 sepa-
rately. The calculation of the intermodulation distortion is as
per the THD specification where it is the ratio of the rms sum of
the individual distortion products to the rms amplitude of the
fundamental expressed in dB.
4
, V
5
, and V
THD dB
1
is the rms amplitude of the fundamental and V
(
6
are the rms amplitudes of the second through the
)
S
/2 and excluding dc) to the rms value of the
=
20
log
V
2
2
+
V
3
2
+
V
V
1
4
2
+
V
5
2
+
V
6
2
REV. C
2
, V
3
,