SNAS801B June 2020 – June 2021 LMK05318B
PRODUCTION DATA
Figure 9-2 shows the PLL architecture implemented in the LMK05318B. The primary "PLL1" channel consists of a digital PLL (DPLL) and analog PLL (APLL1) with integrated BAW VCO (VCO1) capable of generating clocks with RMS phase jitter of 50-fs typical. A secondary APLL (APLL2) with integrated LC VCO (VCO2) can be used as an additional clock generation domain with RMS phase jitter of 130-fs typical.
The DPLL is comprised of a time-to-digital converter (TDC), digital loop filter (DLF), and 40-bit fractional feedback (FB) divider with sigma-delta-modulator (SDM). The APLLs are comprised of a reference (R) divider, phase-frequency detector (PFD), loop filter (LF), fractional feedback (N) divider with SDM, and VCO. APLL2 has a reference selection mux that allows APLL2 to be either locked to the VCO domain of the APLL1 (Cascaded APLL2) or locked to the XO input (Non-Cascaded APLL2). Otherwise, APLL2 can be disabled (powered-down) if this clock domain is not needed. The VCO of the APLL1 feeds the output clock distribution blocks directly, whereas the VCO of the APLL2 drives the clock distribution blocks through the VCO post-dividers.
The following sections describe the basic principle of operation for DPLL mode and APLL-only mode. See Section 9.4.2 for more details on the PLL modes of operation including holdover.