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Operational Mode Descriptions

SYSTEM

CLOCK

Figure 2

shows the LVPSCB configured as a zero skew clock buffer. In this mode the CY7B9911V is used as the basis for a low skew

clock distribution tree. When all the function select inputs (xF0, xF1) are left open, each of the outputs are aligned and drive a

terminated transmission line to an independent load. The FB input is tied to any output in this configuration and the operating frequency

range is selected with the FS pin. The low skew specification, along with the ability to drive terminated transmission lines (with

impedances as low as 50Ω), enables efficient printed circuit board design.

SYSTEM

CLOCK

Figure 3

shows a configuration to equalize skew between metal

traces of different lengths. In addition to low skew between

outputs, the LVPSCB is programmed to stagger the timing of its

outputs. Each of the four groups of output pairs is programmed

to different output timing. Skew timing is adjusted over a wide

range in small increments with the appropriate strapping of the

function select pins. In this configuration the 4Q0 output is sent

back to FB and configured for zero skew. The other three pairs

of outputs are programmed to yield different skews relative to the

feedback. By advancing the clock signal on the longer traces or

Document Number: 38-07408 Rev. *D

Figure 2. Zero Skew and Zero Delay Clock Driver

REF

4Q0

4F0

4Q1

4F1

3Q0

3F0

3Q1

3F1

2F0

2Q0

2F1

2Q1

1F0

1Q0

1F1

1Q1

TEST

LENGTH L1 = L2 = L3 = L4

Figure 3. Programmable Skew Clock Driver

REF

4Q0

4F0

4Q1

4F1

3Q0

3F0

3Q1

3F1

2F0

2Q0

2F1

2Q1

1F0

1Q0

1F1

1Q1

TEST

LENGTH L1 = L2

L3 < L2 by 6 inches

L4 > L2 by 6 inches

retarding the clock signal on shorter traces, all loads receive the

clock pulse at the same time.

Figure 3

the FB input is connected to an output with 0 ns skew

(xF1, xF0 = MID) selected. The internal PLL synchronizes the FB

and REF inputs and aligns their rising edges to make certain that

all outputs have precise phase alignment.

Clock skews are advanced by ±6 time units (tU) when using an

output selected for zero skew as the feedback. A wider range of

delays is possible if the output connected to FB is also skewed.

Since "Zero Skew", +tU, and –tU are defined relative to output

CY7B9911V

3.3V RoboClock+™

LOAD

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