SNAS522K September 2011 – December 2023 LMK03806
PRODUCTION DATA
The LMK03806 has an the ability to be driven by an external reference. Typical external reference interfaces are shown in Figure 8-2 and Figure 8-3.
In applications where the external reference amplitude is less than the VOSCin specification of 2.4 Vpp Figure 8-2 is an appropriate method of interfacing the reference to the LMK03806.
In applications where the external reference amplitude is greater than the VOSCin specification of 2.4 Vpp Figure 8-3 is an appropriate method of interfacing the reference to the LMK03806.
In both cases C1 and C2 should be present a low impedance at the reference frequency. A typical value for C1 and C2 is 0.1 µF.
Using an external reference, such as a crystal oscillator (XO), may provide better phase noise than a crystal at offsets below the loop bandwidth. If the jitter integration bandwidth for the application of interest is above the loop filter bandwidth, the added phase noise of a crystal will not be a significant jitter contributor and may be a more cost effective solution than an XO. Also, operating at higher reference frequencies allows higher phase detector frequencies, which also improves in band PLL phase noise performance.