ICS84330C 데이터 시트보기 (PDF) - Integrated Circuit Systems

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ICS84330C

700MHZ, LOW JITTER, CRYSTAL-TO-3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER

Integrated Circuit Systems 

Integrated

Circuit

Systems, Inc.

ICS84330C

700MHZ, LOW JITTER, CRYSTAL-TO-3.3V

DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER

JITTER REDUCTION FOR FREF_EXT SINGLE END INPUT

If the FREF_EXT input is driven by a 3.3V LVCMOS driver, the

jitter performance can be improved by reducing the amplitude

swing and slowing down the edge rate. Figure 7A shows an

amplitude reduction approach for a long trace. The swing will

be approximately 0.85V for logic low and 2.5V for logic high

(instead of 0V to 3.3V). Figure 7B shows amplitude reduction

approach for a short trace. The circuit shown in Figure 7C

reduces amplitude swing and also slows down the edge rate

by increasing the resistor value.

VDD

Ro ~ 7 Ohm RS

43

Driver_LVCMOS

Zo = 50 Ohm

Td

VDD

R1

100

R2

100

VDD

GND

TEST_CLK

FREF_EXT

FIGURE 7A. AMPLITUDE REDUCTION FOR A LONG TRACE

VDD

Ro ~ 7 Ohm RS

100

Driver_LVCMOS

VDD

R1

200

R2

200

VDD

GND

TEST_CLK

FREF_EXT

FIGURE 7B. AMPLITUDE REDUCTION FOR A SHORT TRACE

VDD

Ro ~ 7 Ohm RS

200

Driver_LVCMOS

VDD

R1

400

R2

400

VDD

GND

TEST_CLK

FREF_EXT

84330CV

FIGURE 7C. EDGE RATE REDUCTION BY INCREASING THE RESISTOR VALUE

www.icst.com/products/hiperclocks.html

12

REV. B DECEMBER 7, 2004

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