PM5380-BI PMC-Sierra, Inc., PM5380-BI Datasheet - Page 406

• Manufacturer Part Number: PM5380-BI
• Description: Network Interface, SATURN User Network Interface (8x155) Telecom Standard Product
• Manufacturer: PMC-Sierra, Inc.

Proprietary and Confidential to PMC-Sierra, Inc., and for its customers’ internal use.
Document No.: PMC- 2010299, Issue 2
13.16 High Speed PECL Interfaces
In normal operation, the S/UNI-8x155 performs clock and data recovery on the incoming serial
stream. The device is designed for optical modules without clock and data recovery such as
HFCT/HFBR-5208 transceivers.
Only a few passive components are required to convert the optical transceivers signals to ECL
(or PECL) logic levels. Figure 34 and Figure 35 illustrate the recommended configurations for
both types of ECL voltage levels when connecting to optical modules. Note that the
RXD[7:0]+/- inputs are internally terminated with a 100 ohm resistor between the differential
inputs. The SPECLV must be set appropriately to configure the RXD[7:0]+/- and SD[7:0] for
the optical module being used. The SD also supports TTL input which may be enabled using
the SDTTL input.
The TXD[7:0]+/- outputs are AC coupled so that the ECL inputs of the optical module are free
to swing around the ECL bias voltage (V
1.3volts lower than the supply. The bias voltage may be generated using a resistor divided as
shown in Figure 35. The bias voltage may shared between optical modules if the resistor
divider is well decoupled and star connected to the termination networks. Otherwise, data
dependent jitter may be coupled between optic modules.
The TXD+/- outputs on the S/UNI-8x155 swing approximately 3.3V and requires the
combination of the series source resistor and the termination resistors to divide the output
voltage down to a nominally 800mV swing. The series resistor attenuates the signal as well as
damping any signal reflections from the optics module. Calculations involving the series
resistor must include the 15 to 20 ohm source resistance of the TXD[7:0]+/- output drivers.
The 50 ohm control impedance traces reduce the effect of signal reflections between the optical
module and the S/UNI-8x155. Vias should be avoided on the signal path between the optical
module and the S/UNI-8x155 as they can affect the jitter performance of the interface. Vias
may be used for the termination networks as the inductive effective of a via will not
significantly affect the termination performance.
When a RXD[7:0]+/- PECL input is not being used, the positive differential input must be tied
to analog power (AVD) and the negative differential input must be tied to analog ground (AVS).
In all cases, the PECL inputs must be driven with a differential voltage (do not connect both
pins to AVD or AVS). When a TXD[7:0]+/- PECL output is not being used, the pins must be
left floating.
S/UNI®-8x155 ASSP Telecom Standard Product Data Sheet
BB
). In general, the ECL bias voltage is referenced
Released
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