lxt6155 Intel Corporation, lxt6155 Datasheet - Page 19

• Manufacturer Part Number: lxt6155
• Description: 155 Mbps Sdh/sonet/atm Transceiver
• Manufacturer: Intel Corporation

2.3.3
2.4
2.4.1
2.4.2
2.4.3
2.5
Datasheet
(LOS=High) or Rx PLL loss of lock (LOCK=Low) conditions RSOCLK P/N is switched to the Tx
serial clock. Also the serial output data is forced to all zeros. This feature can be disabled in SW
mode (HWSEL = High) via register #10, bit #7.
Crystal Reference Clock (XTALIN/XTALOUT)
An optional 19.44 MHz crystal can be connected across the XTALIN and XTALOUT pins. This
crystal reference provides an onchip clock that is independent of the external system clock
(TSICLKP/TSICLKN or TPICLK). The main functions of the crystal reference clock are threefold:
(1) to center the receive PLL at 155 MHz, (2) to keep the PLL centered at 155 MHz when LOS
asserts, and (3) In the event incoming data is lost, to provide a reference clock for other devices
which require it. The designer has the option to use this crystal reference clock or the transmit input
clock (TSICLKP/TSICLKN or TPICLK) to center the receive PLL.
Jitter
The Bellcore GR-253 standard defines jitter as the “short-term variations of a digital signal’s
significant instants from their ideal positions in time”. Significant instants are the optimum data
sampling instants. Jitter parameters can be measured at the line interface, with system interface in
loopback mode, yielding jitter accumulated in both transmitter and receiver. Isolated jitter
measurements for transmitter and receiver can also be performed. Jitter specs are divided into three
categories: jitter tolerance, jitter generation, and jitter transfer. Jitter values, in effect, measure the
performance of the receive PLL and the transmit synthesizer PLL.
Jitter Tolerance
Jitter tolerance is the peak-to-peak amplitude of sinusoidal jitter applied at the line interface input
that causes an equivalent 1 dB SNR loss measured as BER = 10
page 44
Jitter Generation (Intrinsic Jitter)
Jitter generation is the amount of transmit jitter at the output of the equipment with a jitter-free
transmit input data and clock. For SONET/SDH, jitter generation is less than 0.01 UI rms,
measured with a band-pass filter from 12 kHz to 1.3 MHz. Refer to 27 on page 45 for the LXT6155
performance.
Jitter Transfer
Jitter transfer is defined as the ratio of output jitter to input jitter amplitude versus jitter frequency
for a given bit rate. Input jitter amplitude is shown in the Jitter Tolerance curve. Output jitter is
under the Jitter Transfer template. Refer to Figures 27 and 28 on pages and for the LXT6155
performance.
Operational Modes
The LXT6155 functions in both Hardware standalone and Software modes. The operating mode is
set by the state of the HWSEL pin.
for the LXT6155 performance.
155 Mbps SDH/SONET/ATM Transceiver — LXT6155
-10
. Refer to Figure 26 on page
19