Datasheet

AD7357
Rev. B | Page 11 of 20
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 AD7357 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, 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 (see Table 2), 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 (dB).
Thermal Hysteresis
Thermal hysteresis is defined as the absolute maximum change
of the reference output voltage after the device is cycled through
temperature from either
T_HYS+ = 25°C to T
MAX
to 25°C
T_HYS– = 25°C to T
MIN
to 25°C
It is expressed in ppm using the following equation:
6
10
)25(
)_()25(
)ppm( ×
°
−°
=
CV
HYSTVCV
V
REF
REFREF
HYS
where:
V
REF
(25°C) is V
REF
at 25°C.
V
REF
(T_HYS) is the maximum change of V
REF
at T_HYS+ or
T_HYS–.