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AD7328 Datasheet(PDF) 14 Page  Analog Devices 

AD7328 Datasheet(HTML) 14 Page  Analog Devices 
14 / 36 page AD7328 Rev. A  Page 14 of 36 Thermal Hysteresis ChanneltoChannel Isolation Thermal hysteresis is defined as the absolute maximum change of reference output voltage after the device is cycled through temperature from either Channeltochannel isolation is a measure of the level of crosstalk between any two channels. It is measured by applying a fullscale, 100 kHz sine wave signal to all unselected input channels and determining the degree to which the signal attenuates in the selected channel with a 50 kHz signal. Figure 14 shows the worst case across all eight channels for the AD7328. The analog input range is programmed to be the same on all channels. T_HYS+ = +25°C to TMAX to +25°C or T_HYS− = +25°C to TMIN to +25°C It is expressed in ppm using the following equation: 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 0. For example, the secondorder terms include (fa + fb) and (fa − fb), whereas the thirdorder terms include (2fa + fb), (2fa − fb), (fa + 2fb), and (fa − 2fb). 6 10 ) 25 ( ) _ ( ) 25 ( ) ( × ° − ° = C V HYS T V C V ppm V REF REF REF HYS where: VREF(25°C) is VREF at 25°C. VREF(T_HYS) is the maximum change of VREF at T_HYS+ or T_HYS−. CMRR (CommonMode Rejection Ratio) The AD7328 is tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the secondorder terms are usually distanced in frequency from the original sine waves, whereas the thirdorder terms are usually at a frequency close to the input frequencies. As a result, the second and thirdorder terms are specified separately. The calculation of the intermodulation distortion is 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. CMRR is defined as the ratio of the power in the ADC output at fullscale frequency, f, to the power of a 100 mV sine wave applied to the commonmode voltage of the VIN+ and VIN− frequency, fS, as CMRR (dB) = 10 log (Pf/PfS) where Pf is the power at frequency f in the ADC output, and PfS is the power at frequency fS in the ADC output (see Figure 17). PSR (Power Supply Rejection) Variations in power supply affect the fullscale transition but not the linearity of the converter. Power supply rejection is the maximum change in the fullscale transition point due to a change in power supply voltage from the nominal value (see the Typical Performance Characteristics section). 
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