82P33813 datasheet(23/70 Pages) RENESAS

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September 5, 2017

82P33813 Datasheet

3.3.2.3

Combo Mode

Figure 13 shows a high level diagram of the Combo mode using fre-

quency control and Figure 14 shows a high level diagram of the Combo

mode using phase control. The 82P33813 uses the disciplined DCO to

provide a stable time base for the IEEE 1588 clock recovery servo algo-

rithm.

In this mode, two PLL cores are used. DPLL1 (or DPLL2) will be

locked to the physical layer clock the second DCO will be controlled by

IEEE 1588 clock recovery servo algorithm. The IEEE 1588 timestamps

are used to calculate the phase offset between the IEEE 1588 master’s

1 PPS pulse and the IEEE 1588 slave’s 1 PPS pulse and then align the

two pulses by moving the slave’s 1 PPS pulse in phase. The slave must

be able to move the 1 PPS pulse by +/- 0.5 s, and the 82P33813 pro-

vides this capability.

The combo mode is very useful for implementations of T-BC per ITU-

T Recommendations. ITU-T Recommendation G.8271.1defines congru-

ent and non-congruent scenarios. Congruent scenario is defined when

both the physical layer frequency and phase/time follow the same syn-

chronization path, and non-congruent scenario is defined when both the

physical layer frequency and phase/time do not follow the same syn-

chronization path. As it is stated in G.8271.1, the non-congruent sce-

nario represents a worst-case for the combination of PTP and SDH/

SyncE.

The combo mode was designed to deal with the worst case scenario

when the physical layer clock and the IEEE 1588 clock are not traceable

to the same primary reference (e.g. the physical layer clock is traceable

to the Primary Reference Clock (PRC) and the IEEE 1588 clock is trace-

able to the Primary Reference Time Clock (PRTC)). In this scenario the

Telecom Slave clock will have to track 2 different frequencies: the physi-

cal layer frequency and the IEEE 1588 frequency. An alternative way of

combining SyncE and IEEE 1588 is to initially frequency lock to a SyncE

clock as the input reference, then the slave switches to the IEEE 1588

packet stream as the timing reference. This method will only work if the

SyncE clock and the IEEE 1588 timing are traceable to the same PRTC.

It is recommended to use the Combo mode as it will work in both cases:

when the physical layer clock and the IEEE 1588 clock are not traceable

to the same primary reference, and also when they are traceable to the

same primary reference.

The advantage of the combo mode is that the physical layer clock

and the IEEE 1588 timing can be traceable to two separate and inde-

pendent timing paths. There can be a significant frequency offset

between the two without causing any problems in the slave clock. Both

the physical layer clock and the IEEE 1588 clock can be recovered and

filtered independently for wander and jitter by the slave clock

This is done all inside the device, no need to route the clocks exter-

nally. It is also important to be able to control phase transients in the

SyncE clock. This can be done by either using an internal filter that will

filter the SyncE transients, or by suppressing the SyncE transients

based on SSM clock quality level.

Figure 13. Combo mode using frequency control

LPF

DCO

SyncE

Clock

DPLL1

LPF

DCO

Output

Clock

Frequency

Offset

Microport

Interface

Phase

Offset

Microport

DPLL1/2

System

Clock

Oscillator

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