Altera Corporation
2–61
October 2007
Stratix II GX Device Handbook, Volume 2
Stratix II GX Transceiver Architecture Overview
Receiver PLL
Each transceiver block contains four receiver PLLs, which receive the
reference clock to train the VCO used by the CRU to match the phase and
frequency of the reference clock.
Figure 2–51
shows the block diagram for
the lock-to-reference portion as the receiver PLL is active.
Table 2–15
lists
some of the PLL specifications.
Table 2–16
lists the available /M and /L
values within the receiver PLL.
Figure 2–51. Receiver PLL Block Diagram
Note to
Figure 2–51
:
(1)
Values of /M and /L counters are specified in
Table 2–16
. The Quartus II software selects these values automatically
based on the data rate and the selected reference clock frequencies.
f
This section focuses on the receiver PLL in lock-to-reference mode only
(the receiver is not active in lock-to-data mode). The lock-to-data mode is
discussed in the section
“Clock Recovery Unit” on page 2–63
. For
information on the operation between the lock-to-reference and
lock-to-data modes, refer to
“Lock-to-Reference and Lock-to-Data
Modes” on page 2–64
.
The receiver PLL has an optional lock indicator,
rx_pll_locked
, which
indicates when the receiver PLL is phase and frequency locked to the
reference clock. The
rx_pll_locked
is an active high signal. A high
signal indicates that the PLL is phase and frequency-locked to a reference
clock, a low signal indicates that the PLL is not locked to the reference
clock. If the CRU is locked to the incoming data, the
rx_pll_locked
port may toggle (assert and deassert) because the phase and/or
frequency differences between the recovered clock and the reference
clock might be large enough to trigger a loss of lock. This is an expected
behavior because the receiver PLL is inactive in the lock-to-data mode
rx_cruclk
CP+LF
Up
Down
VCO
/M
rx_datain
High-Speed Recovered Clock
Low-Speed Recovered Clock
Down
Up
rx_locktorefclk
rx_locktodata
rx_freqlocked
Clock Recovery Unit Control
PFD
/L
÷
2
÷
N
÷
1, 2, 4
÷
1, 2, 4
Inactive Circuits
Active Circuits
rx_pll_locked