zl50064 Zarlink Semiconductor, zl50064 Datasheet - Page 23

• Manufacturer Part Number: zl50064
• Description: 16 K Channel Digital Switch With High Jitter Tolerance, Single Rate 2, 4, 8 Or 16 Mbps And 64 Input And 64 Output Streams
• Manufacturer: Zarlink Semiconductor

by jitter. There are, however, some cases where data experience more delay than the timing signals. A common
example is when multiple data lines are tied together to form bidirectional buses. The large bus loading may cause
data to be delayed. If this is the case, the optimum sampling point may be 3/4 or 4/4 instead of 1/2. The optimum
sampling point is dependent on the application. The user should optimize the sampling point to achieve the best
jitter tolerance performance.
2.5
Input clock jitter tolerance depends on the data rate. In general, the higher the data rate, the smaller the jitter
tolerance is, because the period of a bit cell is shorter, and the sampling point variation allowance is smaller.
Jitter tolerance can not be accurately represented by just one number. Jitter of the same amplitude but different
frequency spectrum can have different effect on the operation of a device. For example, a device that can tolerate
20ns of jitter of 10kHz frequency may only be able to tolerate 10ns of jitter of 1MHz frequency. Therefore, jitter
tolerance should be represented as a spectrum over frequency. The highest possible jitter frequency is half of the
carrier frequency. In the case of the ZL50062/64, the input clock is 8.192MHz, and the jitter associated with this
clock can have the highest frequency component at 4.096MHz.
For the above reasons, jitter tolerance of the ZL50062/64 has been characterized at 16.384Mbps. The lower data
rates (2.048Mbps, 4.096Mbps, 8.192Mbps) will have the same or better tolerance than that of the 16.384Mbps
operation. Tolerance of jitter of different frequencies are shown in the “AC Electrical Characteristics“ section, table
“Input Clock Jitter Tolerance“ on page 62. The Jitter Tolerance Improvement Circuit was enabled (Control Register,
bit FBDEN set HIGH, and bits FBD_MODE[2:0] set to 111
3.0
Various registers are used to control the input sampling point (delay) and the output advancement for the Local and
Backplane streams. The following sections explain the details of these offset programming features.
3.1
Control of the Input Bit Delay allows each input stream to have a different frame boundary with respect to the
master frame pulse, FP8i. Each input stream can be individually delayed by up to 7 3/4 bits with a resolution of 1/4
bit of the bit period.
3.1.1
Input Bit Delay Registers LIDR0-31 and BIDR0-31 work in conjunction with the SMPL_MODE bit in the Control
Register to allow users to control input bit fractional delay as well as input bit sample point selection for greater
flexibility when designing switch matrices for high speed operation.
When SMPL_MODE = LOW (input bit fractional delay mode), bits LID[4:0] and BID[4:0] in the LIDR0-31 and
BIDR0-31 registers respectively define the input bit fractional delay of the corresponding local and backplane
stream. The total delay can be up to 7 3/4 bits with a resolution of 1/4 bit at the selected data rate. When
SMPL_MODE = HIGH (sampling point select mode), bits LID[1:0] and BID[1:0] define the input bit sampling point of
the stream. The sampling point can be programmed at the 3/4, 4/4, 1/4 or 2/4 bit location to allow better tolerance
for input jitter. Bits LID[4:2] and BID[4:2] define the integer input bit delay, with a maximum value of 7 bits at a
resolution of 1 bit.
Refer to Figure 9 and Figure 10 for Input Bit Delay Timing at 16Mbps and 8Mbps data rates, respectively.
Refer to Figure 10 for Input Sampling Point Selection Timing at 8Mbps data rates.
Input Clock Jitter Tolerance
Input Offsets
Input and Output Offset Programming
Input Bit Delay Programming (Backplane and Local Input Streams)
Zarlink Semiconductor Inc.
ZL50062/4
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B
), and the sampling point was optimized.
Data Sheet