CS61582 datasheet(11/32 Pages) CIRRUS

11 / 32 page

The clock recovery circuit is a second-order

phase locked loop that can tolerate up to 0.4 UI

of jitter from 10 kHz to 100 kHz without gener-

ating errors (Figure 7). The clock and data

recovery circuit is tolerant of long strings of con-

secutive zeros and will successfully recover a

1-in-175 jitter-free line input signal.

Recovered data at RPOS and RNEG is stable

and may be sampled using the recovered clock

RCLK. The CLKE input determines the clock

polarity where the output data is stable and valid

as shown in Table 2. When CLKE is low, RPOS

and RNEG are valid on the rising edge of

RCLK. When CLKE is high, RPOS and RNEG

are valid on the falling edge of RCLK.

CLKE

DATA

CLOCK

Clock Edge

for Valid Data

LOW

RPOS

RNEG

RCLK

Rising

HIGH

RPOS

RNEG

RCLK

Falling

Table 2. Recovered Data/Clock Options

JITTER ATTENUATOR

The jitter attenuator is located in the transmit

path of each channel to remove gapped clock jit-

ter on TCLK. Figure 8 illustrates the typical

jitter attenuation curve.

The attenuator consists of a 64-bit FIFO, a nar-

row-band monolithic PLL, and control logic.

Signal jitter is absorbed in the FIFO which is de-

signed to neither overflow nor underflow. If

overflow or underflow is imminent, the jitter

transfer function is altered to insure that no bit-

errors occur. Under this condition, jitter gain

may occur and jitter should be attenuated exter-

nally in a frame buffer. The jitter attenuator will

typically tolerate 43 UIs before the overflow/un-

d erflo w mechanism occu rs. If the jitter

attenuator has not had time to "lock" to the aver-

age incoming frequency (e.g., following a device

reset) the attenuator will tolerate a minimum of

22 UIs before the overflow/underflow mecha-

nism occurs. The attenuator can accept a

transmit clock with gaps

≤ 28 UIs and a transmit

clock burst rate of

≤ 8 MHz.

When a loss of signal occurs, the last recovered

frequency is not held and the output frequency be-

comes the frequency of the reference clock.

REFERENCE CLOCK

The CS61582 requires a reference clock with a

minimum accuracy of

±100 ppm for T1 and E1

applications. This clock can be either a 1X clock

(i.e., 1.544 MHz or 2.048 MHz), or can be a 8X

clock (i.e., 12.352 MHz or 16.384 MHz) as se-

10k

1 00

100k

70 0

100

300

30 0

PE AK-TO -PEAK

JITTER

(unit in te rv als)

J ITT E R F R E Q UE NCY (H z)

C S 61582

P e rform ance

138

A T& T 62411

(1990 V e rsion)

Figure 7. Minimum Input Jitter Tolerance of Receiver

F requ ency in H z

100

1 k

10 k

b ) Ma ximum

A tte n uatio n

Lim it

6 2411 (199 0 V ersion)

R e quirem ents

a) M in im u m A tte nua tion Lim it

C S 61582 P e rform an ce

Figure 8. Typical Jitter Transfer Function

DS224PP1

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