JAJSO88 October 2023 LMK04714-Q1
PRODUCTION DATA
The loop filter acts as a low-pass filter that accumulates correction currents from the charge pump and converts those correction currents into a voltage. The loop filter determines the PLL loop bandwidth, which has a dramatic effect on the performance of the PLL since it directly impacts the phase noise, spur level, and switching speed of the device. The loop filter component values are dependent on the phase detector frequency, charge pump gain, and the gain of the VCO.
Loop filter design involves trade-offs. Choosing the optimal bandwidth is application dependent. Minimizing jitter may lead to higher spur levels and a longer lock time; therefore, determining the loop filter components varies by application, as well.
of how to use this tool to obtain an optimal loop filter design that aims to minimize jitter. On this example, the FPD
= 245.76 MHz, KPD = 3.2 mA, and the KVCO = 12.1 MHz/V (this values are also application dependent) which
resulted in an external loop filter of C1 = 220 pF, C2 = 68 nF, and R2 = 120 Ω.
PLL2 has an integrated loop filter of C1i = 60 pF, R3 = 2400 Ω, C3 = 50 pF, R4 = 200 Ω and C4 = 10 pF as shown in Figure 8-9. Loop filter components C1, C2, and R2 can be solved using the PLLatinumSim software