AD7468 Analog Devices, AD7468 Datasheet - Page 16

• Manufacturer Part Number: AD7468
• Description: 1.6 V Micro-Power 8-Bit ADC
• Manufacturer: Analog Devices

Specifications of AD7468

• Resolution (bits): 8bit
• # Chan: 1
• Sample Rate: 200kSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: SOP,SOT

AD7466/AD7467/AD7468
TERMINOLOGY
Integral Nonlinearity (INL)
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function. For the AD7466/
AD7467/AD7468, the endpoints of the transfer function are
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 (DNL)
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).
Gain Error
The deviation of the last code transition (111 . . . 110) to
(111…111) from the ideal (that is, V
error has been adjusted out.
Track-and-Hold Acquisition Time
The time required for the part to acquire a full-scale step
input value within ±1 LSB, or a 30 kHz ac input value within
±0.5 LSB. The AD7466/AD7467/AD7468 enter track mode on
the CS falling edge, and return to hold mode on the third SCLK
falling edge. The parts remain in hold mode until the following
CS falling edge. See Figure 3 and the Serial Interface section for
more details.
Signal-to-Noise Ratio (SNR)
The measured ratio of signal to noise at the output of the ADC.
The signal is the rms value of the sine wave input. Noise is the
rms quantization error within the Nyquist bandwidth (f
The rms value of the sine wave is half of its peak-to-peak value
divided by √2, and the rms value for the quantization noise is
q/√12. The ratio depends on the number of quantization levels
in the digitization process; the more levels, the smaller the
quantization noise.
For an ideal N-bit converter, the SNR is defined as
Thus, for a 12-bit converter, it is 74 dB; for a 10-bit converter, it
is 62 dB; and for an 8-bit converter, it is 50 dB.
However, in practice, various error sources in the ADCs cause
the measured SNR to be less than the theoretical value. These
errors occur due to integral and differential nonlinearities,
internal ac noise sources, and so on.
SNR = 6.02 N + 1.76 db
REF
− 1 LSB) after the offset
S
/2).
Rev. C | Page 16 of 28
Signal-to-Noise and Distortion Ratio (SINAD)
The measured ratio of signal-to-noise and distortion at the
output of the ADC. The signal is the rms value of the sine wave,
and noise is the rms sum of all nonfundamental signals up to
half the sampling frequency (f
excluding dc.
Total Unadjusted Error (TUE)
A comprehensive specification that includes gain error, linearity
error, and offset error.
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental. For
the AD7466/AD7467/AD7468, it is defined as
where V
V
sixth harmonics.
Peak Harmonic or Spurious Noise (SFDR)
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 specifica-
tion is determined by the largest harmonic in the spectrum, but
for ADCs where the harmonics are buried in the noise floor, it
is a noise peak.
Intermodulation Distortion (IMD)
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 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 AD7466/AD7467/AD7468 are tested using the CCIF
standard where two input frequencies 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 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 sum
of the fundamentals, expressed in dB.
4
, V
THD
5
, and V
1
is the rms amplitude of the fundamental, and V
( )
dB
6
are the rms amplitudes of the second through
=
20
log
V
2
2
+
S
S
/2), including harmonics, but
/2 and excluding dc) to the rms
V
3
2
+
V
V
1
4
2
+
V
5
2
+
V
6
2
2
, V
3
,