EP3SE50F780I3N Altera, EP3SE50F780I3N Datasheet - Page 328

• Manufacturer Part Number: EP3SE50F780I3N
• Description: Stratix III
• Manufacturer: Altera

Programmable Pre-Emphasis and Programmable VOD
Programmable
Pre-Emphasis
and
Programmable
VOD
Figure 9–10. Programmable VOD
9–12
Stratix III Device Handbook, Volume 1
OUT
OUT
Synchronizer
The synchronizer is a 1-bit × 6-bit deep FIFO buffer that compensates for
the phase difference between the recovered clock from the DPA circuit
and the diffioclk that clocks the rest of the logic in the receiver. The
synchronizer can only compensate for phase differences, not frequency
differences between the data and the receiver’s INCLK.
An optional port, RX_FIFO_RESET, is available to the internal logic to
reset the synchronizer. The synchronizer is automatically reset when the
DPA first locks to the incoming data. Altera recommends using
RX_FIFO_RESET to reset the synchronizer when the DPA signals a
loss-of-lock condition beyond the initial locking condition.
Stratix III LVDS transmitters support programmable pre-emphasis and
programmable VOD. Pre-emphasis increases the amplitude of the high
frequency component of the output signal, and thus helps compensate for
the frequency dependent attenuation along the transmission line.
Figure 9–10
is produced by pre-emphasis. This overshoot should not be included in
the VOD voltage. The definition of VOD is also shown in
Pre-emphasis is an important feature for high-speed transmission.
Without pre-emphasis, the output current is limited by the VOD setting
and the output impedance of the driver. At high frequency, the slew rate
may not be fast enough to reach the full VOD before the next edge,
producing a pattern dependent jitter.
illustrates an LVDS output with pre-emphasis. The overshoot
VOD
Overshoot
Overshoot
Altera Corporation
Figure
November 2007
9–10.