Cypress Semiconductor CY7B991 Arkusz specyfikacji - Strona 14

Przeglądaj online lub pobierz pdf Arkusz specyfikacji dla Sprzęt komputerowy Cypress Semiconductor CY7B991. Cypress Semiconductor CY7B991 20 stron. Cypress programmable skew clock buffer specification sheet

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range since the highest frequency output is running at 20 MHz.

Figure 7

shows some of the functions that are selectable on the

3Qx and 4Qx outputs. These include inverted outputs and

outputs that offer divide-by-2 and divide-by-4 timing. An inverted

output enables the system designer to clock different

subsystems on opposite edges, without suffering from the pulse

asymmetry typical of non-ideal loading. This function enables

each of the two subsystems to clock 180 degrees out of phase

and align within the skew specifications.

The divided outputs offer a zero delay divider for portions of the

system that need the clock divided by either two or four, and still

remain within a narrow skew of the "1X" clock. Without this

feature, an external divider is added, and the propagation delay

20 MHz

DISTRIBUTION

CLOCK

Document Number: 38-07138 Rev. *B

Figure 7. Multi-Function Clock Driver

REF

4F0

4Q0

4Q1

4F1

3Q0

3F0

3Q1

3F1

2Q0

2F0

2Q1

2F1

1Q0

1F0

1Q1

1F1

TEST

of the divider adds to the skew between the different clock

signals.

These divided outputs, coupled with the Phase Locked Loop,

enables the PSCB to multiply the clock rate at the REF input by

either two or four. This mode enables the designer to distribute

a low frequency clock between various portions of the system,

and then locally multiply the clock rate to a more suitable

frequency, still maintaining the low skew characteristics of the

clock driver. The PSCB performs all of the functions described in

this section at the same time. It multiplies by two and four or

divides by two (and four) at the same time. In other words, it is

shifting its outputs over a wide range or maintaining zero skew

between selected outputs.

80 MHz

INVERTED

20 MHz

80 MHz

ZERO SKEW

80 MHz

SKEWED –3.125 ns (–4t

)

CY7B991

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