CS61304A Cirrus Logic, Inc., CS61304A Datasheet - Page 12

• Manufacturer Part Number: CS61304A
• Description: T1-E1 Line Interface Unit for CPE-ISDN PRI
• Manufacturer: Cirrus Logic, Inc.

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.
12
1 : 2
RTIP
RRING
Figure 10. Receiver Block Diagram
Detector
Slicer
Level
Edge
Data
Continuously
Delay Line
Calibrated
Extraction
PEAK-TO-PEAK
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.
Sampling
Figure 11. Minimum Input Jitter Tolerance of Receiver
Selector
(unit intervals)
Phase
Clock
Clock
Data
JITTER
&
(Clock Recovery Circuit and Jitter Attenuator)
300
138
100
28
10
.4
.1
1
1
Attenuator
AT&T 62411
Jitter
10
JITTER FREQUENCY (Hz)
Minimum
Performance
100
300
CS61304A
RPOS
RNEG
RCLK
700
1k
DS156PP2
10k
100k