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參數(shù)資料
| 型號(hào)： | S4503 |
| 廠商： | Applied Micro Circuits Corp. |
| 英文描述： | BiCMOS Clock Synthesizer(帶可編程時(shí)鐘輸出的BiCMOS時(shí)鐘合成器) |
| 中文描述： | BiCMOS工藝時(shí)鐘合成器（帶可編程時(shí)鐘輸出的BiCMOS工藝時(shí)鐘合成器） |
| 文件頁(yè)數(shù)： | 5/10頁(yè) |
| 文件大小： | 117K |
| 代理商： | S4503 |
Applied Micro Circuits Corporation
6195 Lusk Blvd., San Diego, CA 92121 (619) 450-9333
Page 5
S4503
CLOCK SYNTHESIZER
FILTER AND VCO COMPONENT
SELECTION
The S4503 is designed to operate over a wide range
of VCO frequencies. Because of this, it is necessary
to modify the values of Rspan and Rfcenter in order
to get the best performance at a given frequency.
When operating the S4503 with the VCO in the 150–
225 MHz region, the values for the VCO components
are:
Rspan = 470 Ohms, Rfcenter = 390 Ohms
When operation the S4503 with the VCO in to 225–
300 Mhz, the values for the VCO components are:
Rspan = 390 Ohms, Rfcenter = 820 Ohms
The loop filter components, Rcomp and Ccomp, do
not change values at different frequencies. The cor-
rect values for these components are:
Rcomp = 2.7K Ohms, Ccomp = 0.1uF
All of the resistor values are 5% and 1/8 watt.
20pF
2M
CRYSTAL
20pF
S4503
26
25
Decoupling capacitors of 0.1 and 0.01 uF are
needed. Three pairs should be placed as close
to the S4503 power and ground pins as pos-
sible. One pair should be used to decouple the
analog VCC and GND, while the others are for the
digital supplies. The Vtt supply will also need to
be decoupled using 0.1 and 0.01 uF capacitors.
These components should be surface mounted
chip capacitors, to reduce the parasitic induc-
tance.
No dynamic signal lines should pass through or
beneath the filter circuitry area, to avoid the
possibility of noise due to crosstalk.
The crystal oscillator will need to have a 2 M
ohm shunt resistor connected between the ter-
minals of the external crystal, and two 20 pF
capacitors connected from each pin of the crys-
tal to VCC (or GND). These components are
necessary to ensure the oscillator will operate at
the correct frequency.
The loop filter and VCO components must be
surface mounted to reduce the parasitic induc-
tance, and the components are connected to the
analog power and ground planes, rather than the
digital planes.
BOARD LAYOUT CONSIDERATIONS
To minimize the impact of board noise on the opera-
tion of the S4503, the following guidelines should be
followed.
The analog VCCA and GNDA need to be iso-
lated from the digital supplies. This can be ac-
complished by creating small analog power and
ground planes next to the S4503 under the filter
and VCO components. These analog planes
can be connected to the digital planes through
wire jumpers, small inductors (5-100 uH), or fer-
rite beads. If the digital supply noise is too large
(>100mV), the inductors or ferrite beads will be
necessary.
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