参数资料
型号: 843004AGI-01T
厂商: INTEGRATED DEVICE TECHNOLOGY INC
元件分类: 时钟产生/分配
英文描述: 170 MHz, OTHER CLOCK GENERATOR, PDSO24
封装: 4.40 X 7.80 MM, 0.925 MM HEIGHT, MO-153, TSSOP-24
文件页数: 2/19页
文件大小: 1414K
代理商: 843004AGI-01T
ICS843004AGI-01 REVISION B MARCH 24, 2011
10
2011Integrated Device Technology, Inc.
ICS843004I-01 Data Sheet
FEMTOCLOCK CRYSTAL-TO-3.3V, 2.5V LVPECL FREQUENCY SYNTHESIZER
Overdriving the XTAL Interface
The XTAL_IN input can be overdriven by an LVCMOS driver or by
one side of a differential driver through an AC coupling capacitor. The
XTAL_OUT pin can be left floating. The amplitude of the input signal
should be between 500mV and 1.8V and the slew rate should not be
less than 0.2V/nS. For 3.3V LVCMOS inputs, the amplitude must be
reduced from full swing to at least half the swing in order to prevent
signal interference with the power rail and to reduce internal noise.
Figure 3A shows an example of the interface diagram for a high
speed 3.3V LVCMOS driver. This configuration requires that the sum
of the output impedance of the driver (Ro) and the series resistance
(Rs) equals the transmission line impedance. In addition, matched
termination at the crystal input will attenuate the signal in half. This
can be done in one of two ways. First, R1 and R2 in parallel should
equal the transmission line impedance. For most 50
applications,
R1 and R2 can be 100
. This can also be accomplished by removing
R1 and changing R2 to 50
. The values of the resistors can be
increased to reduce the loading for a slower and weaker LVCMOS
driver. Figure 3B shows an example of the interface diagram for an
LVPECL driver. This is a standard LVPECL termination with one side
of the driver feeding the XTAL_IN input. It is recommended that all
components in the schematics be placed in the layout. Though some
components might not be used, they can be utilized for debugging
purposes. The datasheet specifications are characterized and
guaranteed by using a quartz crystal as the input.
Figure 3A. General Diagram for LVCMOS Driver to XTAL Input Interface
Figure 3B. General Diagram for LVPECL Driver to XTAL Input Interface
VCC
XTAL_OUT
XTAL_IN
R1
100
R2
100
Zo = 50 ohms
Rs
Ro
Zo = Ro + Rs
C1
.1uf
LVCMOS Driver
XTAL_OUT
XTAL_IN
Zo = 50 ohms
C2
.1uf
LVPECL Driver
Zo = 50 ohms
R1
50
R2
50
R3
50
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