AD7862ARZ-2 Analog Devices Inc, AD7862ARZ-2 Datasheet - Page 6

• Manufacturer Part Number: AD7862ARZ-2
• Description: DUAL 12-BIT PARALLEL ADC I.C.
• Manufacturer: Analog Devices Inc

Specifications of AD7862ARZ-2

• Number Of Bits: 12
• Sampling Rate (per Second): 250k
• Data Interface: Parallel
• Number Of Converters: 2
• Power Dissipation (max): 75mW
• 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

AD7862
TERMINOLOGY
Signal to (Noise + Distortion) Ratio
This is the measured ratio of signal to (noise + distortion) at the
output of the A/D converter. The signal is the rms amplitude of
the fundamental. Noise is the rms sum of all nonfundamental
signals up to half the sampling frequency (f
The ratio is dependent upon the number of quantization levels
in the digitization 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.
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the rms sum of
harmonics to the fundamental. For the AD7862 it is defined as:
where V
and V
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
m, n = 0, 1, 2, 3, etc. Intermodulation 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 (2 fa + fb), (2 fa – fb), (fa + 2 fb) and
(fa – 2 fb).
The AD7862 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 and third order terms are of different
significance. 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
separately. 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 dBs.
5
Signal to (Noise + Distortion) = (6.02 N + 1.76) dB
are the rms amplitudes of the second through the fifth
1
is the rms amplitude of the fundamental and V
THD dB
S
/2 and excluding dc) to the rms value of the
20 log
V
2
2
V
3
2
V
1
S
V
/2), excluding dc.
4
2
V
2
5
nfb where
2
, V
3
, V
4
–6–
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 100 kHz sine wave signal to each of the four inputs
individually. These, in turn, are individually referenced to the
other three channels whose inputs are grounded, and the ADC
output is measured to determine the level of crosstalk from the
other channel. The figure given is the worst case across all four
channels.
Relative Accuracy
Relative accuracy or endpoint nonlinearity is the maximum
deviation from a straight line passing through the endpoints of
the ADC transfer function.
Differential Nonlinearity
This is the difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Positive Full-Scale Error
This is the deviation of the last code transition (01 . . . 110 to
01 . . . 111) from the ideal 4 VREF – 3/2 LSB (AD7862-10
after the Bipolar Offset Error has been adjusted out.
Positive Full-Scale Error (AD7862-2, 0 V to 2.5 V)
This is the deviation of the last code transition (01 . . . 110 to
01 . . . 111) from the ideal VREF – 3/2 LSB after the unipolar
offset error has been adjusted out.
Bipolar Zero Error (AD7862-10,
This is the deviation of the midscale transition (all 1s to all 0s)
from the ideal AGND – 1/2 LSB.
Unipolar Offset Error (AD7862-2, 0 V to 2.5 V)
This is the deviation of the first code transition (00 . . . 000 to
00 . . . 001) from the ideal AGND + 1/2 LSB.
Negative Full-Scale Error (AD7862-1,
This is the deviation of the first code transition (10 . . . 000 to
10 . . . 001) from the ideal –4 VREF + 1/2 LSB (AD7862-10
after Bipolar Zero Error has been adjusted out.
Track/Hold Acquisition Time
Track/Hold acquisition time is the time required for the output
of the track/hold amplifier to reach its final value, within
track/hold returns to track mode). It also applies to situations
where a change in the selected input channel takes place or
where there is a step input change on the input voltage applied
to the selected V
user must wait for the duration of the track/hold acquisition
time, after the end of conversion or after a channel change/step
input change to V
ensure that the part operates to specification.
10 V range) or VREF – 3/2 LSB (AD7862-3, 2.5 V range)
10 V range) or –VREF + 1/2 LSB (AD7862-3, 2.5 V range)
1/2 LSB, after the end of conversion (the point at which the
2.5 V)
AX/BX
AX/BX
input of the AD7862. It means that the
, before starting another conversion to
10 V, AD7862-3,
10 V; AD7862-3,
2.5 V)
REV. 0