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LTC6957 additive phase noise when the LTC input is square wave


         In the data sheet, the additve phase noise data for LTC6954 is based on the sine wave input. What if the square wave input? In addition, LTC6954 is a limiter,nonlinear products may produce. Does the square wave input go through the limiter still a square wave?

  • Amplitude Noise to Phase Noise conversion is sensitive to the input slew rate.   Up to a point, Faster slew rates limit the amount of amplitude noise to phase noise conversion.  The below slide shows the equation to calculate slew rates for sine waves and square waves.  In other words, if the square wave has an equal or faster slew rate than the sine wave than the additive phase will be equal or possibly better.  

    As long your input does not exceed the maximum input voltage amplitude in the datasheet you should not see any unexpected spurious results due to the input waveform shape.