
Altera Corporation
5–13
July 2005
Stratix Device Handbook, Volume 2
High-Speed Differential I/O Interfaces in Stratix Devices
Figure 5–8. High-Speed 1-to-1 Transmitter Clock Output
(1)
This figure does not show additional circuitry for clock or data manipulation.
Using SERDES
to Implement
DDR
Some designs require a 2-to-1 data-to-clock ratio. These systems are
usually based on Rapid I/O, SPI-4 Phase 2 (POS_PHY Level 4), or
HyperTransport interfaces, and support various data rates. Stratix
devices meet this requirement for such applications by providing a
variable clock division factor. The SERDES clock division factor is set to 2
for double data rate (DDR).
transmitter clock output signal with half the frequency of the data.
For example, when a system is required to transmit 6.4 Gbps with a
2-to-1 clock-to-data ratio, program the SERDES with eight high-speed
channels running at 800 Mbps each. When you set the output clock
division factor (2 for this example), the Quartus II software automatically
assigns a ninth channel as the transmitter clock output. You can edge- or
center-align the transmitter clock by selecting the default PLL phase or
selecting the negative-edge transmitter clock output. On the receiver side,
the clock signal is connected to the receiver PLL's clock.
The multiplication factor W is also calculated automatically. The data rate
divides by the input clock frequency to calculate the W factor. The
deserialization factor (J) may be 4, 7, 8, or 10.
PD9
PD8
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
PD9
PD8
PD7
PD6
PD5
PD4
PD3
PD2
PD1
PD0
Stratix
Logic Array
Transmitter Circuit
Parallel
Register
Serial
Register
Fast
PLL (1)
TXOUT+
TXOUT
×W
TXLOADEN
Inverter