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SLK2501 Datasheet(PDF) 9 Page - Texas Instruments |
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SLK2501 Datasheet(HTML) 9 Page - Texas Instruments |
9 / 22 page www.ti.com Jitter Generation Loop Timing Mode Loss-of-Lock Indicator Loss of Signal Signal Detect Multiplexer Operation Demultiplexer Operation SLK2501 SLLS502C – OCTOBER 2001 – REVISED MARCH 2007 OC-N/STS-N F0 F1 F2 F3 F4 A1 A2 A3 LEVEL (Hz) (Hz) (Hz) (kHz) (kHz) (Ulpp) (Ulpp) (Ulpp) 3 10 30 300 6.5 65 0.15 1.5 15 12 10 30 300 25 250 0.15 1.5 15 24 Not specified 48 10 600 6000 100 1000 0.15 1.5 15 Figure 3. Input Jitter Tolerance The jitter of a serial clock and serial data outputs must not exceed 0.01 UIrms/0.1 UIp-p when a serial data with no jitter is presented to the inputs. The measurement bandwidth for intrinsic jitter is 12 kHz to 20 MHz. When LOOPTIME is high, the clock synthesizer used to serialize the transmit data is bypassed and the timing is provided by the recovered clock. However, REFCLK is still needed for the recovery loop operation. The SLK2501 has a lock detection circuit to monitor the integrity of the data input. When the clock recovery loop is locked to the input serial data stream, the LOL signal goes high. If the recovered clock frequency deviates from the reference clock frequency by more than 100 ppm, LOL goes low. If the data stream clock rate deviates by more than 170 ppm, loss of lock occurs. If the data streams clock rate deviates more than 500 ppm from the local reference clock, the LOL output status might be unstable. Upon power up, the LOL goes low until the PLL is close to phase lock with the local reference clock. The loss-of-signal (LOS) alarm is set high when no transitions appear in the input data path for more than 2.3 µs. The LOS signal becomes active when the above condition occurs. If the serial inputs of the device are ac-coupled to its source, the ac-coupling capacitor needs to be big enough to maintain a signal level above the threshold of the receiver for the 2.3- µs no transition period. Once activated, the LOS alarm pin is latched high until the receiver detects an A1A2 pattern. The recovered clock (RXCLK) is automatically locked to the local reference when LOS occurs. The parallel data (RXDATAx) may still be processed even when LOS is activated. The SLK2501 has an input SIGDET pin to force the device into the loss of signal state. This pin is generally connected to the signal detect output of the optical receiver. Depending on the optics manufacturer, this signal can be either active high or active low. To accommodate the differences, a polarity select (PS) is used. For an active low, SIGDET input sets the PS pin high. For an active high, SIGDET input sets the PS pin low. When the PS signal pin and SIGDET are of opposite polarities, the loss of signal state is generated and the device transmits all zeroes downstream. The 4-bit parallel LVDS data is clocked into an input buffer by a clock derived from the synthesized clock. The data is then clocked into a 4:1 multiplexer. The D0 bit is the most significant bit and is shifted out first in the serial output stream. The serial 2.5 Gbps data is clocked into a 1:4 demultiplexer by the recovered clock. The D0 bit is the first bit that is received in time from the input serial stream. The 4-bit parallel data is then sent to the LVDS driver along with the divided down recovered clock. 9 Submit Documentation Feedback |
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