EVAL-AD7450ACB AD [Analog Devices], EVAL-AD7450ACB Datasheet - Page 10

• Manufacturer Part Number: EVAL-AD7450ACB
• Description: Differential Input, 1 MSPS 10-Bit and 12-Bit ADCs in an 8-Lead SOT-23
• Manufacturer: AD [Analog Devices]

AD7440/AD7450A
TERMINOLOGY
Signal-to-(Noise + Distortion) Ratio
This is the measured ratio of signal to (noise + distortion) at the
output of the ADC. The signal is the rms amplitude of the
fundamental. Noise is the sum of all nonfundamental signals
up to half the sampling frequency (f
ratio is dependent on the number of quantization levels in the
digitization process; the more levels, the smaller the quanti-
zation noise. The theoretical signal-to-(noise + distortion) ratio
for an ideal N-bit converter with a sine wave input is given by
the following:
Thus for a 12-bit converter, this is 74 dB; and for a 10-bit
converter, this is 62 dB.
Total Harmonic Distortion (THD)
THD is the ratio of the rms sum of harmonics to the
fundamental. For the AD7440/AD7450A, it is defined as
where V
V
harmonics.
Peak Harmonic or Spurious Noise
Peak harmonic (spurious noise) is the ratio of the rms value of
the next largest component in the ADC output spectrum (up to
f
Normally, 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, 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 the 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).
S
/2 and excluding dc) to the rms value of the fundamental.
4
, V
5
, and V
Signal-to-(Noise + Distortion) = (6.02N + 1.76)dB.
THD
1
is the rms amplitude of the fundamental and V
6
(
dB
are the rms amplitudes of the second to the sixth
)
=
20
log
V
2
2
+
V
3
S
/2), excluding dc. The
2
+
V
V
4
1
2
+
V
5
2
+
V
6
2
2
, V
3,
Rev. B | Page 10 of 28
The AD7440/AD7450A is tested using the CCIF standard of
two input frequencies near the top end of the input bandwidth.
In this case, the second-order terms are distanced in frequency
from the original sine waves, while the third-order terms are 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.
Aperture Delay
This is the amount of time from the leading edge of the
sampling clock until the ADC actually takes the sample.
Aperture Jitter
This is the sample-to-sample variation in the effective point in
time at which the actual sample is taken.
Full Power Bandwidth
The full power bandwidth of an ADC is 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.
Common-Mode Rejection Ratio (CMRR)
The common-mode rejection ratio is the ratio of the power
in the ADC output at full-scale frequency, f, to the power of a
100 mV p-p sine wave applied to the common-mode voltage of
V
Pf is the power at the frequency f in the ADC output; Pfs is the
power at frequency f
Integral Nonlinearity (INL)
This is the maximum deviation from a straight line passing
through the endpoints of the ADC transfer function.
Differential Nonlinearity (DNL)
This is the difference between the measured and the ideal
1 LSB change between any two adjacent codes in the ADC.
Zero-Code Error
This is the deviation of the midscale code transition
(111...111 to 000...000) from the ideal V
IN+
and V
IN–
of frequency f
CMRR (dB) = 10 log (Pf/Pfs)
S
in the ADC output.
S
as follows:
IN+
− V
IN–
(i.e., 0 LSB).