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參數資料
| 型號： | W42C31-03 |
| 廠商： | Cypress Semiconductor Corp. |
| 英文描述： | Spread Spectrum Frequency Timing Generator(寬頻譜頻率同步產生器) |
| 中文描述： | 擴頻頻率定時發生器（寬頻譜頻率同步產生器） |
| 文件頁數： | 2/6頁 |
| 文件大小： | 136K |
| 代理商： | W42C31-03 |
W42C31-03
2
Functional Description
The W42C31-03 uses a phase-locked loop (PLL) to frequency
modulate an input clock. The result is an output clock whose
frequency is slowly swept over a narrow band near the input
signal. The basic circuit topology is shown in
Figure 1
. An
on-chip crystal driver causes the crystal to oscillate at its fun-
damental. The resulting reference signal is divided by Q and
fed to the phase detector. A signal from the VCO is divided by
P and fed back to the phase detector also. The PLL will force
the frequency of the VCO output signal to change until the
divided output signal and the divided reference signal match
at the phase detector input. The output frequency is then equal
to the ratio of P/Q times the reference frequency. The unique
feature of the Spread Spectrum Clock Generator is that a mod-
ulating waveform is superimposed at the input to the VCO.
This causes the VCO output to be slowly swept across a pre-
determined frequency band.
Because the modulating frequency is typically 1000 times
slower than the fundamental clock, the spread spectrum pro-
cess has little impact on system performance.
Frequency Selection With SSFTG
In Spread Spectrum Frequency Timing Generation, EMI re-
duction depends on the shape, modulation percentage, and
frequency of the modulating waveform. While the shape and
frequency of the modulating waveform are fixed, the modula-
tion percentage may be varied.
Using frequency select bits (FS1:0 pins), various spreading
percentages can be chosen (see
Table 1
).
A larger spreading percentage improves EMI reduction. How-
ever, large spread percentages may either exceed system
maximum frequency ratings or lower the average frequency to
a point where performance is affected. For these reasons,
spreading percentages between ±0.5% and ±2.5% are most
common.
The W42C31 features the ability to select from various spread
spectrum
characteristics.
Selections
W42C31-03 are shown in
Table 1
. Other spreading character-
istics are available (see separate data sheets) or can be cre-
ated with a custom mask.
specific
to
the
Pin Definitions
Pin Name
Pin No.
Pin
Type
Pin Description
CLKOUT
5
O
Output Modulated Frequency
: Frequency modulated copy of the unmodulated input
clock
X1
1
I
Crystal Connection or External Reference Frequency Input:
This pin has dual
functions. It may either be connected to an external crystal, or to an external reference
clock.
X2
2
I
Crystal Connection:
If using an external reference, this pin must be left unconnected.
Output Enable (Active LOW):
This pin three-states the output when HIGH. It has an
internal pull-down resistor.
Frequency Selection Bit 0:
This pin selects the frequency spreading characteristics.
Refer to
Table 1
. This pin has a pull-up resistor.
OE#
8
I
FS0
4
I
FS1
7
I
Frequency Selection Bit 1:
This pin selects the frequency range. Refer to
Table 1
.
This pin has a pull-up resistor.
VDD
6
P
Power Connection:
Connected to 5V power supply.
Ground Connection:
This should be connected to the common ground plane.
GND
3
G
Figure 1. System Block Diagram
XTAL
Freq.
Divider
Q
Phase
Detector
Modulating
Waveform
VCO
Post
Dividers
CLKOUT
Charge
Pump
Feedback
DiP
PLL
GND
VDD
X1
X2
Crystal load
capacitors
as needed
Σ
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相關代理商/技術參數 |
參數描述 |
|---|---|
| W42C31-03G | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Clock Driver |
| W42C31-03GT | 制造商:Cypress Semiconductor 功能描述: |
| W42C31-04 | 制造商:CYPRESS 制造商全稱:Cypress Semiconductor 功能描述:Spread Spectrum Frequency Timing Generator |
| W42C31-04G | 制造商:Cypress Semiconductor 功能描述:Logic and Timing, Spread Spectrum Frequency Timing Generator 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| W42C31-04GT | 制造商:Cypress Semiconductor 功能描述:Logic and Timing, Spread Spectrum Frequency Timing Generator |
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