There is an insatiable thirst for improved phase noise performance from clock and LO synthesizer sources in critical radar and communication systems. The LMX2820 integrated PLL/VCO synthesizer is a very low noise synthesizer solution with programmable frequency from 45 MHz to 22.6 GHz. For applications where squeezing every drop of phase noise performance is important, combining the output of two LMX2820 outputs is an easy and straightforward approach to getting a modest phase noise performance improvement.

Combining two devices to achieve improved noise performance is a common practice. The improvement is possible due to the random nature of noise. When combining two outputs, the signals are correlated meaning they are of equal amplitude and phase. This yields a 6 dB signal increase. The noise is uncorrelated; there are random amplitude and phase differences between the noise signals. The combined incoherent noise yields on average a 3 dB increase. Overall, there is a net 3 dB improvement in signal to noise ratio (SNR) performance.