AD7766-1 AD [Analog Devices], AD7766-1 Datasheet - Page 14

• Manufacturer Part Number: AD7766-1
• Description: 24-Bit, 8.5 mW, 109 dB, 128/64/32 kSPS ADCs
• Manufacturer: AD [Analog Devices]

AD7767
TERMINOLOGY
Signal-to-Noise Ratio (SNR)
SNR is the ratio of the rms value of the actual input signal to the
rms sum of all other spectral components below the Nyquist
frequency, excluding harmonics and dc. The value for SNR is
expressed in decibels.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the fundamen-
tal. For the AD7767, it is defined as
where:
V
V
the sixth harmonics.
Nonharmonic Spurious-Free Dynamic Range (SFDR)
SFDR is the ratio of the rms signal amplitude to the rms value
of the peak spurious spectral component, excluding harmonics.
Dynamic Range
Dynamic range is the ratio of the rms value of the full scale to
the rms noise measured with the inputs shorted together. The
value for the dynamic range is expressed in decibels.
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 are equal to 0. 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).
The AD7767 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, 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
1
2
, V
is the rms amplitude of the fundamental.
THD
3
, V
4
, V
( )
dB
5
, and V
=
20
6
log
are the rms amplitudes of the second to
V
2
2
+
V
3
2
+
V
V
1
4
2
+
V
5
2
+
V
6
2
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sum of the individual distortion products to the rms amplitude
of the sum of the fundamentals expressed in decibels.
Integral Nonlinearity (INL)
INL is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function.
Differential Nonlinearity (DNL)
DNL is the difference between the measured and the ideal
1 LSB change between any two adjacent codes in the ADC.
Zero Error
Zero error is the difference between the ideal midscale input
voltage (when both inputs are shorted together) and the actual
voltage producing the midscale output code.
Zero Error Drift
Zero error drift is the change in the actual zero error value due
to a temperature change of 1°C. It is expressed as a percentage
of full scale at room temperature.
Gain Error
The first transition (from 100…000 to 100…001) should occur
for an analog voltage ½ LSB above the nominal negative full
scale. The last transition (from 011…110 to 011…111) should
occur for an analog voltage 1½ LSB below the nominal full
scale. The gain error is the deviation of the difference between
the actual level of the last transition and the actual level of the
first transition, from the difference between the ideal levels.
Gain Error Drift
Gain error drift is the change in the actual gain error value due
to a temperature change of 1°C. It is expressed as a percentage
of full scale at room temperature.
Common-Mode Rejection Ratio (CMRR)
CMRR is defined as the ratio of the power in the ADC output
at full-scale frequency f to the power of a 100 mV sine wave
applied to the common-mode voltage of the V
inputs at frequency fs.
where Pf is the power at the frequency f in the ADC output and
Pfs is the power at the frequency fs in the ADC output.
CMRR (dB) = 10 log(Pf/Pfs)
IN+
and V
IN−