HFBR-0537 Avago Technologies US Inc., HFBR-0537 Datasheet - Page 2

• Manufacturer Part Number: HFBR-0537
• Description: Fiber Optics, Evaluation Kit
• Manufacturer: Avago Technologies US Inc.

Specifications of HFBR-0537

• Tool / Board Applications: Fiber Optic Transceivers
• Mcu Supported Families: HFBR-1527, HFBR-2526
• Development Tool Type: Hardware / Software - Eval/Demo Board
• Main Purpose: Interface, Fiber Optics
• Embedded: No
• Utilized Ic / Part: HFBR-1527, HFBR-2526
• Primary Attributes: DC ~ 32MBd TTL
• Secondary Attributes: TTL-Compatible
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: 516-2146; HFBR-0537

The Pros and Cons of Arbitrary Duty Factor or Burst Mode Data
The most important advantage of any existing data
communication protocol is that it already exists, and
typically works reasonably well with copper wires in
many applications. On the other hand, existing pro-
tocols for copper wire are usually not the best choice
for optimizing the performance of a fiberoptic link. For
example, a receiver designed for use with arbitrary duty
factor data, or burst mode data, will typically be 4 dB to
7 dB less sensitive than when the same components are
used in receiver circuits optimized for use with encoded
data. Encoded data normally has a 50 percent duty fac-
tor, or restricted duty factor variation, which allows the
construction of higher-sensitivity fiberoptic receivers.
The best arbitrary duty factor or burst-mode receivers
described in this application note are considerably less
sensitive than the encoded data receivers described in
AN-1122.
When sending arbitrary duty factor data, a separate op-
tical link must be used to send the clock if synchronous
serial communication is desired, or an asynchronous
data communication system can be implemented if the
data is oversampled by a local clock oscillator located
Figure 1. Relationship Between PWd and Sampling Rate
2
at the receiving end of the fiberoptic data link. To avoid
excessive pulsewidth distortion (PWD), the local oscilla-
tor used to oversample the received data must operate
at frequency that is greater than the serial data rate. For
instance, if the data rate is 32-Mbits/sec, a clock frequen-
cy of 100 MHz will assure three times oversampling of
the received serial data. As the sampling rate decreases,
the PWD of the reclocked data increases. Conversely,
when the sampling rate is increased, the PWD of the
asynchronous data link decreases. At modest data rates
such as 32-Mbits/sec the frequency of the local clock
oscillator will rise sharply if higher oversampling rates
are attempted; for instance, to guarantee five times
oversampling the clock oscillator at the receiver would
need to operate at a frequency slightly greater than 160
MHz. Refer to Figure 1 for a graphical representation of
the relationship between the sampling rate and PWD of
an asynchronous serial data communication link.
The 10Base-T copper standard sends no transitions
between packets of Ethernet data, but the 10Base-FL
standard for optical fiber media inserts a 1 MHz square
wave between each packet of Ethernet traffic.