AD7999 Analog Devices, AD7999 Datasheet - Page 16

• Manufacturer Part Number: AD7999
• Description: 4-Channel, 8-Bit ADC with I2C Compatible Interface in 8-Lead SOT-23
• Manufacturer: Analog Devices

Specifications of AD7999

• Resolution (bits): 8bit
• # Chan: 4
• Sample Rate: 140kSPS
• Interface: I²C/Ser 2-Wire
• Analog Input Type: SE-Uni
• Ain Range: (Vref) p-p,Uni (Vref),Uni Vdd
• Adc Architecture: SAR
• Pkg Type: SOT

AD7991/AD7995/AD7999
TERMINOLOGY
Signal-to-Noise and Distortion (SINAD) Ratio
The measured ratio of signal-to-noise and distortion at the output
of the ADC. The signal is the rms amplitude of the fundamental.
Noise is the sum of the nonfundamental signals excluding dc,
up to half the sampling frequency (f
on the number of quantization levels in the digitization process:
the more levels, the smaller the quantization noise. The theoretical
SINAD ratio for an ideal N-bit converter with a sine wave input
is given by
Therefore, SINAD is 49.92 dB for an 8-bit converter, 61.96 dB
for a 10-bit converter, and 74 dB for a 12-bit converter.
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental. For
the AD7991/AD7995/AD7999, it is defined as
where:
V
V
through 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. Typically, the value of this specification
is determined by the largest harmonic in the spectrum, but for
ADCs where the harmonics are buried in the noise floor, the
largest harmonic may be 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, and so on. Intermodulation distortion terms
are those for which neither m nor n equals 0. For example,
second-order terms include (fa + fb) and (fa − fb), and
third-order terms include (2fa + fb), (2fa − fb), (fa + 2fb), and
(fa − 2fb).
The AD7991/AD7995/AD7999 are tested using the CCIF standard,
where two input frequencies near the maximum input bandwidth
are used. In this case, the second-order terms are usually distanced
1
2
, V
is the rms amplitude of the fundamental.
Signal-to-(Noise + Distortion) = (6.02 N + 1.76) dB
THD
3
, V
4
, V
(
dB
5
, and V
)
=
20
6
log
are the rms amplitudes of the second
V
2
2
+
S
/2 and excluding dc) to the rms
V
3
2
+
S
/2). The ratio is dependent
V
V
4
1
2
+
V
5
2
+
V
6
2
Rev. B | Page 16 of 28
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 intermodulation distortion is, like the THD
specification, the ratio of the rms sum of the individual distortion
products to the rms amplitude of the sum of the fundamentals,
expressed in decibels.
Channel-to-Channel Isolation
Channel-to-channel isolation is a measure of the level of
crosstalk between any two channels. It is measured by applying
a full-scale sine wave signal to all unselected input channels and
then determining the degree to which the signal attenuates in
the selected channel with a 10 kHz signal. The frequency of the
signal in each of the unselected channels is increased from 2 kHz
up to 92 kHz. Figure 14 shows the worst-case across all four
channels for the AD7991.
Full-Power Bandwidth
The input frequency at which the amplitude of the reconstructed
fundamental is reduced by 0.1 dB or 3 dB for a full-scale input.
Integral Nonlinearity
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function. The endpoints are
at zero scale (a point 1 LSB below the first code transition) and
full scale (a point 1 LSB above the last code transition).
Differential Nonlinearity
The difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Offset Error
The deviation of the first code transition (00 … 000 to
00 … 001) from the ideal—that is, AGND + 1 LSB.
Offset Error Match
The difference in offset error between any two channels.
Gain Error
The deviation of the last code transition (111 … 110 to
111 … 111) from the ideal (that is, V
the offset error has been adjusted out.
Gain Error Match
The difference in gain error between any two channels.
REF
− 1 LSB) after