Silicon Laboratories SI5369, SI5365 Fundamental Mode Crystals Reference Drift, Reference Jitter

Si53xx-RM

Fundamental Mode Crystals

For cost sensitive applications that do not have the most demanding jitter requirements, all of the narrow band devices can use fundamental mode crystals that are in the lowest frequency band ranging from 37 to 41 MHz (corresponding to RATE = LL). Unlike the other narrowband members of the family, the Si5327 is only capable of using fundamental mode crystals that are in this range. For a more detailed discussion of the trade-offs associated with this approach and a list of approved low frequency crystals, please see the application note AN591, which can be downloaded from www.silabs.com/timing.

Reference Drift

During Digital Hold, long-term and temperature related drift of the reference input result in a one-to-one drift of the output frequency. That is, the stability of the any-frequency output is identical to the drift of the reference frequency. This means that for the most demanding applications where the drift of a crystal is not acceptable, an external temperature compensated or ovenized oscillator will be required. Drift is not an issue unless the device is in Digital Hold. Also, the initial accuracy of the reference oscillator (or crystal) is not relevant as long as it is within one of the frequency bands described in Table 60.

Reference Jitter

Jitter on the reference input has a roughly one-to-one transfer function to the output jitter over the band from 100 Hz up to about 30 kHz. If the XA/XB pins implement a crystal oscillator, the reference will have suitably low jitter if a suitable crystal is used. If the XA/XB pins are connected to an external reference oscillator, the jitter of the external reference oscillator may also contribute significantly to the output jitter. A typical reference input-to-output jitter transfer function is shown in Figure 59.

38.88MHz XO, 38.88MHz CKIN, 38.88MHz CKOUT

	10
	0
(dB)
Power	-10						Jitter Xfer
	-20
	-30
	1	10	100	1000	10000	100000	1000000

Frequency (Hz)

Figure 59. Typical Reference Jitter Transfer Function

120 Rev. 0.5