ep2c35 Altera Corporation, ep2c35 Datasheet - Page 158

• Manufacturer Part Number: ep2c35
• Description: Cyclone Ii Device Family Data Sheet
• Manufacturer: Altera Corporation

Duty Cycle Distortion
Figure 5–9. DCD Measurement Technique for Non-DDIO (Single-Data Rate) Outputs
5–68
Cyclone II Device Handbook, Volume 1
clk
DCD Measurement Techniques
DCD is measured at an FPGA output pin driven by registers inside the
corresponding I/O element (IOE) block. When the output is a single data
rate signal (non-DDIO), only one edge of the register input clock (positive
or negative) triggers output transitions
present on the input clock signal, or caused by the clock input buffer, or
different input I/O standard, does not transfer to the output signal.
However, when the output is a double data rate input/output (DDIO)
signal, both edges of the input clock signal (positive and negative) trigger
output transitions
clock and the input clock buffer affect the output DCD.
IOE
(T/2 – D1) / T (the low percentage boundary)
(T/2 + D2) / T (the high percentage boundary)
(Figure
DFF
D
5–10). Therefore, any distortion on the input
Q
(Figure
5–9). Therefore, any DCD
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output
February 2008