参数资料
型号: ICS84321
英文描述: 260MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER
中文描述: 260MHZ,水晶到3.3V的差分LVPECL频率合成器
文件页数: 2/18页
文件大小: 204K
代理商: ICS84321
84321AY
www.icst.com/products/hiperclocks.html
REV. B JUNE 9, 2005
10
Integrated
Circuit
Systems, Inc.
ICS84321
260MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL
LVPECL FREQUENCY SYNTHESIZER
V
CC - 2V
50
Ω
50
Ω
RTT
Z
o = 50Ω
Z
o = 50Ω
FOUT
FIN
RTT =
Z
o
1
((V
OH + VOL) / (VCC – 2)) – 2
3.3V
125
Ω
125
Ω
84
Ω
84
Ω
Z
o = 50Ω
Z
o = 50Ω
FOUT
FIN
The clock layout topology shown below is a typical termina-
tion for LVPECL outputs. The two different layouts mentioned
are recommended only as guidelines.
FOUT and nFOUT are low impedance follower outputs that
generate ECL/LVPECL compatible outputs.Therefore, terminat-
ing resistors (DC current path to ground) or current sources
must be used for functionality. These outputs are designed to
FIGURE 2B. LVPECL OUTPUT TERMINATION
FIGURE 2A. LVPECL OUTPUT TERMINATION
V
CC - 2V
drive 50
Ω transmission lines. Matched impedance techniques
should be used to maximize operating frequency and minimize
signal distortion.
Figures 2A and 2B show two different layouts
which are recommended only as guidelines. Other suitable clock
layouts may exist and it would be recommended that the board
designers simulate to guarantee compatibility across all printed
circuit and clock component process variations.
TERMINATION FOR LVPECL OUTPUTS
APPLICATION INFORMATION
CRYSTAL INPUT INTERFACE
The ICS84321 has been characterized with 18pF parallel reso-
nant crystals.The capacitor values shown in
Figure 3 below were
determined using a 25MHz, 18pF parallel resonant crystal and
were chosen to minimize the ppm error. These same capacitor
values will tune any 18pF parallel resonant crystal over the fre-
quency range of 14MHz to 40MHz providing the other param-
eters specified in
Table 6, Crystal Characteristics, are satisfied.
Figure 3. CRYSTAL INPUt INTERFACE
C1
18p
X1
18pF Parallel Crystal
C2
22p
XTAL_IN
XTAL_OUT
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ICS84321AY 260MHZ, CRYSTAL-TO-3.3V DIFFERENTIAL LVPECL FREQUENCY SYNTHESIZER
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