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SY87701VZC Datasheet(PDF) 3 Page - Micrel Semiconductor |
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SY87701VZC Datasheet(HTML) 3 Page - Micrel Semiconductor |
3 / 12 page SY87701V 3 Micrel FUNCTIONAL DESCRIPTION Clock Recovery Clock Recovery, as shown in the block diagram generates a clock that is at the same frequency as the incoming data bit rate at the Serial Data input. The clock is phase aligned by a PLL so that it samples the data in the center of the data eye pattern. The phase relationship between the edge transitions of the data and those of the generated clock are compared by a phase/frequency detector. Output pulses from the detector indicate the required direction of phase correction. These pulses are smoothed by an integral loop filter. The output of the loop filter controls the frequency of the Voltage Controlled Oscillator (VCO), which generates the recovered clock. Frequency stability without incoming data is guaranteed by an alternate reference input (REFCLK) that the PLL locks onto when data is lost. If the Frequency of the incoming signal varies by greater than approximately 1000ppm with respect to the synthesizer frequency, the PLL will be declared out of lock, and the PLL will lock to the reference clock. The loop filter transfer function is optimized to enable the PLL to track the jitter, yet tolerate the minimum transition density expected in a received SONET data signal. This transfer function yields a 30 µs data stream of continuous 1's or 0's for random incoming NRZ data. The total loop dynamics of the clock recovery PLL provides jitter tolerance which is better than the specified tolerance in GR-253-CORE. Lock Detect The SY87701V contains a link fault indication circuit which monitors the integrity of the serial data inputs. If the received serial data fails the frequency test, the PLL will be forced to lock to the local reference clock. This will maintain the correct frequency of the recovered clock output under loss of signal or loss of lock conditions. If the recovered clock frequency deviates from the local reference clock frequency by more than approximately 1000ppm, the PLL will be declared out of lock. The lock detect circuit will pull the input data stream in an attempt to reacquire lock to data. If the recovered clock frequency is determined to be within approximately 1000ppm, the PLL will be declared in lock and the lock detect output will go active. RDOUTP, RDOUTN [Receive Data Output] Differential PECL. These ECL 100K outputs (+3.3V or +5V referenced) represent the recovered data from the input data stream (RDIN). This recovered data is sampled on the rising edge of RCLK. RCLKP, RCLKN [Clock Output] Differential PECL. These ECL 100K outputs (+3.3V or +5V referenced) represent the recovered clock used to sample the recovered data (RDOUT). TCLKP, TCLKN [Clock Output] Differential PECL. These ECL 100K outputs (+3.3V or +5V referenced) represent either the recovered clock (CLKSEL = HIGH) used to sample the recovered data (RDOUT) or the transmit clock of the frequency synthesizer (CLKSEL = LOW). PLLSP, PLLSN [Clock Synthesis PLL Loop Filter] External loop filter pins for the clock synthesis PLL. PLLRP, PLLRN [Clock Recovery PLL Loop Filter] External loop filter pins for the receiver PLL. POWER & GROUND VCC Supply Voltage(1) VCCA Analog Supply Voltage(1) VCCO Output Supply Voltage(1) GND Ground N/C No Connect NOTE: 1. VCC, VCCA, VCCO must be the same value. |
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