CS61577 datasheet(12/44 Pages) ETC

12 / 44 page

put from the phase selector feeds the clock and

data recovery circuits which generate the recov-

ered clock and sample the incoming signal at

appropriate intervals to recover the data.

Data sampling will continue at the periods se-

lected by the phase selector until an incoming

pulse deviates enough to cause a new phase to be

selected for data sampling. The phases of the de-

lay line are selected and updated to allow as much

as 0.4 UI of jitter from 10 kHz to 100 kHz, with-

out error. The jitter tolerance of the receiver

exceeds that shown in Figure 11. Additionally,

this method of clock and data recovery is tolerant

of long strings of consecutive zeros. The data

sampler will continuously sample data based on

its last input until a new pulse arrives to update

the clock phase selector.

The delay line is continuously calibrated using

the crystal oscillator reference clock. The delay

line produces 13 phases for each cycle of the ref-

erence clock. In effect, the 13 phases are

analogous to a 20 MHz clock when the reference

clock is 1.544 MHz. This implementation utilizes

the benefits of a 20 MHz clock for clock recovery

without actually having the clock present to im-

pede analog circuit performance.

In the Hardware Mode, data at RPOS and RNEG

should be sampled on the rising edge of RCLK,

the recovered clock. In the Extended Hardware

Mode, data at RDATA should be sampled on the

falling edge of RCLK. In the Host Mode, CLKE

determines the clock polarity for which output

data should be sampled as shown in Table 5.

10k

100

100k

700

100

300

PEAK-TO-PEAK

JITTER

(unit intervals)

JITTER FREQUENCY (Hz)

AT&T 62411

138

Minimum

Performance

Figure 11. Minimum Input Jitter Tolerance of Receiver

(Clock Recovery Circuit and Jitter Attenuator)

1 : 2

RTIP

RRING

RPOS

RNEG

RCLK

Data

Level

Slicer

Data

Sampling

& Clock

Extraction

Jitter

Attenuator

Edge

Detector

Clock

Phase

Selector

Continuously

Calibrated

Delay Line

Figure 10. Receiver Block Diagram

CS61577

DS155PP2

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