Preliminary Technical Data

AD7265

Intermodulation Distortion

With inputs consisting of sine waves at two frequencies, fa and

fb, any active device with nonlinearities will create distortion

products at sum and difference frequencies of mfa ± nfb where

m, n = 0, 1, 2, 3, etc. 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 AD7265 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 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 dBs.

PSR (Power Supply Rejection)

Variations in power supply will affect the full-scale transition

but not the converter’s linearity. Power supply rejection is the

maximum change in full-scale transition point due to a change

in power supply voltage from the nominal value. See Typical

Performance Curves.

Rev. PrA | Page 9 of 16