AD7764 Analog Devices, AD7764 Datasheet - Page 15

• Manufacturer Part Number: AD7764
• Description: 24-Bit, 312 kSPS, 109 dB Sigma Delta ADC with On-Chip Buffers and Serial Interface
• Manufacturer: Analog Devices

Specifications of AD7764

• Resolution (bits): 24bit
• # Chan: 1
• Sample Rate: 40MSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: 6.5 V p-p
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

TERMINOLOGY
Signal-to-Noise Ratio (SNR)
The ratio of the rms value of the actual input signal to the rms
sum of all other spectral components below the Nyquist fre-
quency, excluding harmonics and dc. The value for SNR is
expressed in decibels (dB).
Total Harmonic Distortion (THD)
The ratio of the rms sum of harmonics to the fundamental.
For the AD7764, it is defined as
where:
V
V
to the sixth harmonics.
Nonharmonic Spurious-Free Dynamic Range (SFDR)
The ratio of the rms signal amplitude to the rms value of the
peak spurious spectral component, excluding harmonics.
Dynamic Range
The ratio of the rms value of the full scale to the rms noise
measured with the inputs shorted together. The value for
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 is equal to 0. 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 AD7764 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
sum of the individual distortion products to the rms amplitude
of the sum of the fundamentals expressed in decibels.
1
2
, V
is the rms amplitude of the fundamental.
THD
3
, V
4
, V
( )
dB
5
, and V
=
20
log
6
are the rms amplitudes of the second
V
2
2
+
V
3
2
+
V
V
1
4
2
+
V
5
2
+
V
6
2
Rev. A | Page 15 of 32
Integral Nonlinearity (INL)
The maximum deviation from a straight line passing through
the endpoints of the ADC transfer function.
Differential Nonlinearity (DNL)
The difference between the measured and the ideal 1 LSB
change between any two adjacent codes in the ADC.
Zero Error
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
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 1/2 LSB above the nominal negative full
scale. The last transition (from 011…110 to 011…111) should
occur for an analog voltage 1 1/2 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
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.
AD7764