Altera HardCopy II Clock Uncertainty Calculator Uživatelský manuál stáhnout pdf (Strana 29)

Altera Corporation 3–3

HardCopy II Clock Uncertainty Calculator User Guide

Design Case Exceptions

Clock Divider

Figure 3–4 shows an example of a clock divider for intra-clock transfer, in

which CLK1 is accounted for in the clock uncertainty calculator, but not

CLK2. You should add 25 ps to both the setup and hold clock uncertainty

values.

Figure 3–4. Clock Divider for Intra-Clock Transfer

Ripple Clock

Figure 3–5 shows a ripple clock as an intra-clock transfer example. A

ripple clock is similar to a divided clock, but uses a different calculation

to account for extra clock uncertainty value.

CLK0 is accounted for by the clock uncertainty calculator, but not CLK1

and CLK2. You need to add 25 ps uncertainty for the CLK1 network and

also add 25 ps uncertainty for the CLK2 network. Therefore, you should

add 50 ps on both setup and hold clock uncertainty for the example

shown in Figure 3–5.

Figure 3–5. Ripple Clock for Intra-Clock Transfer

PLL

INBUF

Source

Clock

Destination

Clock

Source

Destinatio

CLK1

CLK2

CLK3

CLK1

clk_a

clk_b

CLK1

LK0

reg_c reg_d

CLK2

1 2 ... 24 25 26 27 28 29 30 31 32 33 34 ... 61 62

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Altera HardCopy II Clock Uncertainty Calculator Uživatelský manuál Strana 29