ad7921arm-reel Analog Devices, Inc., ad7921arm-reel Datasheet - Page 12

• Manufacturer Part Number: ad7921arm-reel
• Description: 2-channel, 2.35 V To 5.25 V 250 Ksps, 10-/12-bit Adcs
• Manufacturer: Analog Devices, Inc.

AD7911/AD7921
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 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).
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The AD7911/AD7921 are tested using the CCIF standard,
where two input frequencies are used (see fa and fb in the
Specifications section). 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-order and third-
order terms are specified separately. The calculation of the
intermodulation distortion is as in the THD specification,
where it is defined as the ratio of the rms sum of the individual
distortion products to the rms amplitude of the sum of the
fundamentals expressed in dB.