AD7863ARS-10REEL7 View Datasheet(PDF) - Analog Devices
Part Name
Description
MFG CO.
AD7863ARS-10REEL7 Datasheet PDF : 25 Pages
| |||
TOTAL HARMONIC DISTORTION (THD)
Total harmonic distortion (THD) is the ratio of the rms sum of
harmonics to the rms value of the fundamental. For the
AD7863, THD is defined as
( ) THD dB = 20 log V22 + V32 + V42 + V52
V1
(3)
where:
V1 is the rms amplitude of the fundamental.
V2, V3, V4, and V5 are the rms amplitudes of the second through
the fifth harmonic.
THD is also derived from the FFT plot of the ADC output
spectrum.
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 . . . Intermodulation terms are those for which
neither m nor n is equal to zero. 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).
In this case, the second and third order terms are of different
significance. 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 fundamental expressed in dBs. In this case, the input
consists of two equal amplitude, low distortion sine waves.
Figure 15 shows a typical IMD plot for the AD7863.
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
–110
–120
–130
–140
–150
0
INPUT FREQUENCIES
F1 = 50.13kHz
F2 = 49.13kHz
fSAMPLE = 175kHz
IMD
2ND ORDER TERM
–98.21dB
3RD ORDER TERM
–93.91dB
10 20 30 40 50 60 70 80 90
FREQUENCY (kHz)
Figure 15. IMD Plot
AD7863
PEAK HARMONIC OR SPURIOUS NOISE
Harmonic or spurious noise is defined as the ratio of the rms
value of the next largest component in the ADC output
spectrum (up to fS/2 and excluding dc) to the rms value of the
fundamental. Normally, the value of this specification is
determined by the largest harmonic in the spectrum, but for
parts where the harmonics are buried in the noise floor, the
peak is a noise peak.
DC LINEARITY PLOT
Figure 16 and Figure 17 show typical DNL and INL plots for
the AD7863.
1.0
0.5
0
–0.5
–1.0
0
1.0
2048 4096 6144 8192 10240 12288 14336 16383
ADC CODE
Figure 16. DC DNL Plot
0.5
0
–0.5
–1.0
0
2048
4096 6144 8192 10240 12288 14336 16383
ADC CODE
Figure 17. DC INL Plot
Rev. B | Page 15 of 24
Share Link: 