SAF784X datasheet(32/93 Pages) NXP

32 / 93 page

SAF784X_2

Product data sheet

Rev. 02 — 9 May 2008

32 of 93

NXP Semiconductors

SAF784x

One chip CD audio device with integrated MP3/WMA decoder

6.5.5.5

Available signals for monitoring

The operation of the bit detector can be monitored by the microcontroller via an external

pin. Five signals are available for measurement:

PLL frequency signal: The microcontroller monitors this signal by reading register

PLLIntegrator.

Asymmetry signal: This signal is in 2’s complement form and can be read from register

SlicerAssym.

Jitter signal: A jitter measurement is done internally. The zero-crossing jitter value is

available in register PLLJitter.

Internal lock ﬂags.

Jitter signal:

Jitter measurement is done in two steps:

1. The distance between the EFM zero transition and the bit clock zero transition is

measured.

2. The calculated jitter for the zero transition is averaged using a 10-bit low-pass ﬁlter.

The top 8-bits of the ﬁlter output can be read back from register PLLJitter. To obtain

the jitter in % of the channel bit clock, Equation 3 applies:

(3)

This jitter measurement is also available via the Meas1 telemetry signal on pin CL1. The

full 10-bit output of the ﬁlter is available via this pin; see Section 6.5.5.8.

It is also possible to read out an average jitter value via register PLLAverageJitter. This

value is an average of the normal jitter value over a period of 8000 bit clock periods. The

formula to transform this into a percentage is shown in Equation 4:

(4)

6.5.5.6

Use of jitter measurement

The jitter measurement is an absolute-reference jitter measurement. It gives the average

square value of the bit detection jitter. Note that bit-to-clock jitter is measured. In this

device, the bit-to-clock jitter is measured directly before the bit detection, and contains

contributions due to various imperfections of the complete signal path:

• Disc

Table 6.

Jitter input calculation

Distance (

× f

bit)

Average distance (bit clocks)

Jitter ﬁlter input (5-bit decimal

integer)

< 2

⁄

16 to

⁄

16 to

⁄

> 6

⁄

jitter

jitter 7:0

[] 2.83

–

1024

--------------------------------------------

100 %

()

average jitter

averagejitter 7:0

[] 2.83

–

1024

-----------------------------------------------------------------

100

()

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