AD5590BBC datasheet(25/44 Pages) AD

25 / 44 page

AD5590

Rev. 0 | Page 25 of 44

ADC Peak Harmonic or Spurious Noise

Peak 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 deter-

mined by the largest harmonic in the spectrum, but for ADCs

where the harmonics are buried in the noise floor, it is a

noise peak.

ADC 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 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 ADC 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 whereas 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.

AD5590BBC датащи(PDF) 25 Page - Analog Devices