AD7825 Analog Devices, AD7825 Datasheet - Page 8

• Manufacturer Part Number: AD7825
• Description: 3 V/5 V, 2 MSPS, 8-Bit, 1-/4-/8-Channel Sampling ADCs
• Manufacturer: Analog Devices

Specifications of AD7825

• Resolution (bits): 8bit
• # Chan: 4
• Sample Rate: 2MSPS
• Interface: Par
• Analog Input Type: SE-Uni
• Ain Range: 2 V p-p,2.5V p-p
• Adc Architecture: Pipelined
• Pkg Type: DIP,SOIC,SOP

AD7822/AD7825/AD7829
TERMINOLOGY
Signal-to-(Noise + Distortion) Ratio
The measured ratio of signal-to-(noise + distortion) at the
output of the analog-to-digital 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
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 an 8-bit converter, this is 50 dB.
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental. For
the AD7822/AD7825/AD7829, it is defined as
where V
V
sixth harmonics.
Peak Harmonic or Spurious Noise
The ratio of the rms value of the next largest component in the
ADC output spectrum (up to f
value of the fundamental. Normally, the value of this specification
is determined by the largest harmonic in the spectrum, but for
parts where the harmonics are buried in the noise floor, it is a
noise peak.
Intermodulation Distortion
With inputs consisting of sine waves at two frequencies, fa and
fb, any active device with nonlinearities creates distortion
products at sum and difference frequencies of mfa ± nfb, where
m, n = 0, 1, 2, 3, … . Intermodulation terms are those for which
neither m nor n is equal to zero. For example, the second-order
terms include (fa + fb) and (fa − fb), and the third-order terms
include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb).
S
4
/2), excluding dc. The ratio is dependent upon the number of
, V
Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB
THD
5
, and V
1
is the rms amplitude of the fundamental and V
(dB)
6
are the rms amplitudes of the second through the
=
20
log
V
S
2
/2 and excluding dc) to the rms
2
+
V
3
2
+
V
V
1
4
2
+
V
5
2
+
2
V
, V
6
3
2
,
Rev. C | Page 8 of 28
The AD7822/AD7825/AD7829 are 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,
and 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 decibels (dB).
Channel-to-Channel Isolation
A measure of the level of crosstalk between channels. It is
measured by applying a full-scale 20 kHz sine wave signal to
one input channel and determining how much that signal is
attenuated in each of the other channels. The figure given is the
worst case across all four or eight channels of the AD7825 and
AD7829, respectively.
Relative Accuracy or Endpoint Nonlinearity
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function.
Differential Nonlinearity
The difference between the measured and the ideal one LSB
change between any two adjacent codes in the ADC.
Offset Error
The deviation of the 128th code transition (01111111) to
(10000000) from the ideal, that is, V
Offset Error Match
The difference in offset error between any two channels.
Zero-Scale Error
The deviation of the first code transition (00000000) to
(00000001) from the ideal; that is, V
5 V ± 10%), or V
Full-Scale Error
The deviation of the last code transition (11111110) to (11111111)
from the ideal; that is, V
or V
MID
+ 1.0 V − 1 LSB (V
MID
− 1.0 V + 1 LSB (V
MID
DD
+ 1.25 V − 1 LSB (V
= 3 V ± 10%).
MID
MID
.
DD
− 1.25 V + 1 LSB (V
= 3 V ± 10%).
DD
= 5 V ± 10%),
DD
=