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參數(shù)資料
| 型號： | AN-06 |
| 英文描述： | SY89429A Frequency Synthesis |
| 中文描述： | SY89429A頻率合成 |
| 文件頁數(shù)： | 3/12頁 |
| 文件大?。?/td> | 189K |
| 代理商： | AN-06 |
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APPLICATION NOTE
AN-06
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1
Table 1. M & N Combinations For Generating OC-3
and Related Frequencies
In addition to using a single SY89429A, multiple
SY89429As in conjunction with dividers may be used to
achieve multiple required frequencies. There are many
companion divider products offered by Micrel-Synergy for
these applications. SY100EL32 is a divider by 2 and
SY100EL33 is a divider by 4. SY100S834 is a divider by 1,
2, 4 or 2, 4, 8 while SY100S838 is a divider by 1, 2/3 or 2,
4/6. Figure 9 and 10 show examples of using SY89429A in
conjuction with dividers to generate all OC-3 and related
frequencies using 19.44MHz and 16.384MHz clock,
respectively. The MR (Master Reset) pins are used to
synchronize all frequency outputs.
Voltage Controlled Crystal Oscillator
Applications
SY89429A is a PLL (Phase Locked Loop) based
frequency synthesizer with on chip crystal oscillator. With a
16MHz crystal connected in series with varactors as shown
in Figure 11, the oscillator frequency can easily be pulled
by
±
1000ppm. Since the output frequency is directly
proportional to the cyrstal oscillator frequency, the output
frequency is pulled by the same amount (in ppm) as the
crystal oscillator.
Pulse Shaping Application
For applications where 50% duty cycle clock is important,
SY89429A may be the perfect solution. Many clock
Oscillators or signals from the back plane do not provide
the required 50% duty cycle. The problem may be corrected
by simply using the SY89429A as a 1X frequency multiplier.
The
FOUT
output will always maintain 50% duty cycle.
However, phase relationship between the input and output
may not be maintained. For frequencies between 25MHz
and 200MHz, use the SY89429A as a 1X multiplier. For
frequencies between 200MHz and 400MHz, use a divide by
2 stage as a prescaler and the SY89429A as a 2X frequency
multiplier as shown in Figure 12.
frequency is programmed by properly configuring the internal
dividers and can be represented by this formula (See Table
1 for an application example):
FOUT
FXTAL
8
M
N
=
×
Step Size
FXTAL
8
1
N
=
×
FVCO
FXTAL
8
M
=
×
where
FXTAL
is the crystal frequency or input reference frequency
M
is the VCO frequency multiplier (from 2 to 511)
N
is the post divider (2, 4, 8, or 16)
FVCO
is the VCO frequency
Crystal oscillator frequency is designed to be less than
25MHz using a fundamental crystal. In many applications,
wider range of input reference frequency can be used. Input
frequencies at the low end is limited to above 6.26MHz due
to minimum VCO frequency of 400MHz. Input frequency at
the high end is limited by the speed of the phase detector
and should not exceed 200MHz.
Frequency Multiplication Applications
As mentioned before, FOUT is a function of M and N.
Therefore, output frequency may be set to any multiplication
factor as long as the following is valid:
1)
2)
3)
M
is an integer between 2 to 511 inclusive
N
is 2, 4, 8, or 16
Input reference frequency is more than 6.26MHz and
less than 200MHz
VCO
frequency is more than 400MHz and less than
800MHz
4)
Using the FOUT equation, it is very easy to determine
what M and N values must be for a certain multiplication
factor.
One area of interest is communication. The frequencies
often encountered are 155.52MHz for OC-3 or STS-3 and
51.84MHz for OC-1 or STS-1 standard SONET rates. The
following table is a summary of how these frequencies may
be generated:
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