SNAS835A September 2022 – February 2025 LMK5B33414
PRODUCTION DATA
Each APLL has a 40-bit fractional-N divider to support high-resolution frequency synthesis and very low phase noise and jitter. Each APLL also has the ability to tune the VCO frequency through sigma-delta modulator (SDM) control in DPLL mode. In cascaded mode, each APLL has the ability to lock the VCO frequency to another VCO frequency.
In free-run mode, the BAW APLL uses the XO input as an initial reference clock to the VCBO. The PFD of the BAW APLL compares the fractional-N divided clock with the reference clock and generates a control signal. The control signal is filtered by the BAW APLL loop filter to generate a control voltage to set the VCBO output frequency. The SDM modulates the N divider ratio to get the desired fractional ratio between the PFD input and the VCBO output. The other conventional APLL with the LC VCO operates similar to the VCBO. User can select the reference from either the VCBO clock or the XO clock.
In DPLL mode, the APLL fractional SDM is controlled by the DPLL loop to pull the VCO frequency into lock with the DPLL reference input. For example, Figure 8-6 shows how the APLL1 or APLL2 can derive the references from the VCBO if the respective DPLL1 or DPLL2 are disabled. The VCO1 or VCO2 is then effectively locked to the DPLL3 reference input, assuming there is no synthesis error introduced by the fractional N divide ratio of APLL1 or APLL2.