Transmitter Clocking
The fractional PLL generates the parallel clocks (rx_outclock and tx_outclock), the load enable (
LVDS_LOAD_EN
)
signal and the
diffioclk
signal (the clock running at serial data rate) that clocks the load and shift registers.
You can statically set the serialization factor to x4, x5, x6, x7, x8, x9, or x10 using the Quartus II software.
The load enable signal is derived from the serialization factor setting.
You can configure any Cyclone V transmitter data channel to generate a source-synchronous transmitter
clock output. This flexibility allows the placement of the output clock near the data outputs to simplify board
layout and reduce clock-to-data skew.
Different applications often require specific clock-to-data alignments or specific data-rate-to-clock-rate
factors. You can specify these settings statically in the Quartus II MegaWizard Plug-In Manager:
• The transmitter can output a clock signal at the same rate as the data—with a maximum output clock
frequency that each speed grade of the device supports.
• You can divide the output clock by a factor of 1, 2, 4, 6, 8, or 10, depending on the serialization factor.
• You can set the phase of the clock in relation to the data using internal PLL option of the ALTLVDS
megafunction. The fractional PLLs provide additional support for other phase shifts in 45° increments.
The following figure shows the transmitter in clock output mode. In clock output mode, you can use an
LVDS channel as a clock output channel.
Figure 5-36: Transmitter in Clock Output Mode
diffioclk
LVDS_LOAD_EN
Transmitter Circuit
T
Txclkout–
FPGA
Fabric
Fractional
PLL
Parallel
Series
Related Information
Guideline: Use PLLs in Integer PLL Mode for LVDS
on page 5-12
Serializer Bypass for DDR and SDR Operations
You can bypass the serializer to support DDR (x2) and SDR (x1) operations to achieve a serialization factor
of 2 and 1, respectively. The I/O element (IOE) contains two data output registers that can each operate in
either DDR or SDR mode.
I/O Features in Cyclone V Devices
Altera Corporation
CV-52005
Transmitter Clocking
5-64
2014.01.10