LMX2592: LMX2592 & PLLatinum Sim

PLL_FLK is the flicker noise contribution. PLL_FLR is the figure-of-merit (FOM) contribution.

Flicker noise has a characteristic 10dB/decade slope, is independent of phase detector frequency, and tends to increase with carrier frequency. The datasheet specifies the flicker noise as the coefficient PLL_1/f, at the 10kHz offset, normalized to a 1GHz carrier (and since we know the slope, we can calculate the flicker contribution for any offset). PLLatinum Sim calculates the PLL_FLK noise contribution by PLL_1/f + 20*log(Fout/1GHz) - 10*log(offset/10kHz), where offset is the carrier offset for which the flicker contribution is calculated.

FOM noise is a white noise contribution from the phase detector, charge pump, and a handful of other sources (multiplier, post-r, etc). The FOM noise improves by 20dB/decade decrease in N-divider, and decreases by 10dB/decade with increasing phase detector frequency, for a net improvement of 10dB/decade as the phase detector frequency varies. By convention, FOM is specified in the datasheet as the coefficient PLL_FOM, normalized to 1Hz phase detector frequency (for convenient math and impressive-sounding marketing numbers). PLLatinum Sim calculates the PLL_FLR contribution by PLL_FOM + 20*log(N) + 10*log(Fpd/1Hz).

Both of these noise sources sum with the reference noise, and both the PLL and reference noise contributions are attenuated by the loop filter, above which the VCO noise and eventually the output noise floor becomes dominant.

For a detailed discussion of these behaviors, see Chapter 23 of PLL Performance, Simulation, and Design, a book written by one of our engineers to elaborate on these topics.