AN-07 [ETC]
SY89429/30V Frequency Synthesis ; SY89429 / 30V频率合成\n
| 型号： | AN-07 |
| 厂家： | 
ETC |
| 描述： | SY89429/30V Frequency Synthesis
|
| 文件： | 总8页 (文件大小：135K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SY89429/30V
FREQUENCY
SYNTHESIS
APPLICATION NOTE
AN-07
Introduction
General Requirements
Micrel-Synergy’s SY89429/30V frequency synthesizers
Operating the SY89429/30V is very simple. Very few low
are designed to be used in various clock subsystems. The cost external components are required. These low cost
Primary function of the product is to synthesize clock external components provide the tuning capability needed
frequencies required for systems needing a high quality, to optimize and minimize jitter characteristics in each
low jitter clock source.
individual system application. To achieve the best possible
The cost of other clock sources, either crystal or SAW performance in jitter and power supply noise rejection, basic
oscillators, increase dramatically as precision/frequency high speed design guidelines should be followed.
requirements of digital systems push into the 100+ MHz
Power Supply Requirements
arena. Many low cost CMOS frequency synthesizers
appeared in the market in the last few years. Unfortunately,
these products have relatively high jitter and limited operating
frequency range. Therefore, their applications are limited to
lower precision/lower frequencies.
SY89429/30V, designed with Micrel-Synergy’s high
performance ASSET™ Bipolar technology and differential
ECL circuit technology throughout, is a perfect low cost
alternative to the expensive crystal or SAW oscillators. Unlike
other frequency synthesizers, SY89429/30V has extremely
low jitter and high supply noise rejection that ECL is famous
for.
Because the devices are programmable between 25MHz
to 950MHz using a 16MHz crystal, different system
frequency requirements can all use the same device. This
may dramatically reduce inventory costs and management
of additional products otherwise required to achieve these
various frequencies. This programmability also makes board/
system speed grading possible as part of the normal
production flow without multiple oscillators. This provides
higher overall yield and lower manufacturing cost.
In addition to cost savings, there are many other benefits
to using the SY89429/30V. Normal system production testing
can incorporate frequency margining that is unavailable to
fixed frequency designs as in crystal or SAW oscillators.
This capability leads directly to higher product quality and
reliability. Furthermore, SY89429/30V can be programmed
in small steps (1MHz steps with a 16.000MHz crystal).
Other precise frequencies can be programmed as well. See
section titled “Advanced Frequency Control Applications.”
This ability to provide any frequency eliminates the need for
the high cost custom oscillator alternatives.
SY89429/30V is designed to operate with a single positive
supply of either +3.3V or +5V. The FOUT and /FOUT (the
differential PECL outputs) will interface to PECL inputs using
the same supply voltage. However, SY89429/30V can also
be used in a true ECL systems. For this application, please
refer to the section titled “True ECL Design.”
Power Supply Filtering Techniques
As in any high speed integrated circuits, power supply
filtering is very important. A 0.1µF high frequency by-pass
capacitor should be used between all separate power supply
pins and ground. VCC1, VCC_QUIET, VCC_TTL and VCC_OUT
should be individually connected to the power supply plane
through vias, and a by-pass capacitor should be used for
each pin. To achieve optimum jitter performance, better
power supply isolation is required. In this case a ferrite
bead along with a 1µF and a 0.01µF by-pass capacitor
should be connected to each power supply pin. Figure 4
shows the connections of the power supply filtering using
ferrite beads.
Termination for PECL Outputs
The differential PECL outputs, FOUT and /FOUT, are
open emitter outputs. Therefore, terminating resistors or
current sources must be used for functionality. These outputs
are designed to drive 50Ω transmission lines. Matched
impedance techniques should be used to maximize operating
frequency and minimize wave-form distortion. There are a
few simple termination schemes. Figure 1 shows three
simple termination circuits for a +5V system.
Interface for Inputs
Throughout this application note we refer to a frequency
range of 25MHz to 950MHz. This is only for simplicity
reasons and make the application note applicable to both
devices.
The VCO range for SY89429V and SY89430V are
different. That is, SY89429V has an internal VCO range of
400MHz to 800MHz and an external output frequency of
25MHz to 400MHz. SY89430V has an internal VCO range
of 400MHz to 950MHz and an external output frequency of
50MHz to 950MHz.
The SY89429/30V is designed to interface with TTL
compatible signals. All inputs except XTAL1 and XTAL2 are
TTL compatible. These inputs have internal pull up resistors.
Therefore, any inputs can be left open—open inputs are
logical “1” state. Although inputs can be left open, it is
recommended that open inputs be connected to a power
supply line. These inputs can be connected to a power
supply line (VCC for a logical “1”) or a ground line (VEE for a
logical “0”) directly or through series resistors. Alternatively,
these inputs can also be driven directly from any TTL
compatible signals. XTAL1 and XTAL2 inputs should only
be connected to a crystal.
Rev.: E
Amendment:/0
Issue Date: February 2000
1
APPLICATION NOTE
AN-07
Micrel
Input Reference Frequency and
On-Chip Crystal Oscillator
Filter Design
The filter for any Phase Locked Loop (PLL) based device
deserves special attention. SY89429/30V provides filter pins
for an external filter. A simple three-component passive filter
is recommended for achieving ultra low jitter. Figure 3b
shows the recommended three-components. Due to the
differential design, the filter is connected between
LOOP_FILTER and LOOP_REF pins. With this configuration,
extremely high supply noise rejection is achieved. It is
important that the filter circuit and filter pins be isolated
from any non-common mode coupling and placed in the
VCC plane.
The SY89429/30V is designed based on input reference
frequency of 16MHz and phase detector frequency of 2MHz.
For using other input reference frequencies, refer to section
titled “Advanced Frequency Control Applications.” Using
16MHz reference frequency, the output frequency can be
programmed from 25MHz to 950MHz in 1MHz steps. The
input crystal oscillator requires only an off-chip 16MHz
reference crystal connected between XTAL1 and XTAL2
pins. Figure 3a shows the recommended crystal oscillator
circuit.
Generating High-Speed TTL Clock Signals
A high speed PECL-to-TTL translator such as SY10/
100ELT23 or SY10/100ELT23L (for +3.3V) may be used to
generate high speed TTL compatible signals. High speed
PECL-to-TTL translating Clock Drivers such as SY10/
100H841/842 or SY10/100H641/646 may be added if
multiple copies of such clocks are desired. For 3.3 volt
power supply operation, the following PECL-to-TTL
translating clock drivers SY10/100H841L/842L or SY10/
100H641L/646L may be used. These translators are capable
of driving 50pF loads up to 160MHz.
Using the On-Board Crystal Oscillator
The SY89429/30V features a fully integrated on-board
crystal oscillator to minimize system implementation costs.
The oscillator is a series resonant, multivibrator type design
as opposed to the more common parallel resonant oscillator
design. The series resonant design provides better stability
and eliminates the need for large on chip capacitors. As the
oscillator is somewhat sensitive to loading on its inputs the
user is advised to mount the crystal as close to the SY89429/
30V as possible to avoid any board level parasitics. To
facilitate co-location surface mount crystals are
recommended, but not required.
True ECL Design
The oscillator circuit is a series resonant circuit and thus
for optimum performance a series resonant crystal should
be used. Unfortunately most crystals are characterized in a
parallel resonant mode. Fortunately there is no physical
difference between a series resonant and parallel resonant
crystal. The difference is purely in the way the devices are
characterized. As a result a parallel resonant crystal can be
used with the SY89429/30V with only a minor error in the
desired frequency. A parallel resonant mode crystal used in
a series resonant circuit will exhibit a frequency of oscillation
a few hundred ppm lower than specified, a few hundred
ppm translates to KHz inaccuracies. In a general computer
application this level of inaccuracy is immaterial. Table 1
specifies the performance requirements of the crystals to
be used with the SY89429/30V.
The SY89429/30V is designed for TTL/PECL systems.
However, it can be designed into a pure ECL environment
easily. Connect all VCC pins to ground and all GND pins to
–3.3V, –4.5V (or –5.2V) power supply line. With this
operating condition, FOUT and /FOUT interface directly with
normal 100K ECL signals. All other inputs have internal pull
up resistors. Therefore, any input can be left open and
open inputs are logical “1” state. Although inputs are allowed
to be open, it is recommended that open inputs be connected
to a power supply line. These inputs can be connected to
ground lines (0 volt for a logical “1”) or negative power
supply lines (–3.3V, –4.5V or –5.2V for a logical “0”) directly
or through series resistors. These inputs can interface to
normal ECL signals with SY100ELT23 for signal translation.
Figure 5 shows the schematic with signal translations.
Parameter
Value
Fundamental AT Cut
Series Resonance*
±75ppm at 25°C
±150ppm 0 to 70°C
0 to 70°C
Advanced Frequency Control Applications
The primary function of these products is to synthesize
clock frequencies from 25MHz to 950MHz in 1MHz steps
with a 16.00MHz crystal. However, there are many other
applications that are not so obvious. Even though the
SY89429/30V is said to be able to generate frequencies
between 25MHz to 950MHz in 1MHz steps with a 16MHz
crystal, output frequency is programmed by properly
configuring the internal dividers and can be represented by
this formula (See Table 1 for an application example):
Crystal Cut
Resonance
Frequency Tolerance
Frequency/Temperature Stability
Operating Range
Shunt Capacitance
5-7pF
Equivalent Series Resistance (ESR)
Correlation Drive Level
Aging
50Ω to 80Ω
100µW
5ppm/Yr (First 3 Years)
Table 1. Crystal Specifications
2
APPLICATION NOTE
AN-07
Micrel
Crystal oscillator frequency is designed to be less than
25MHz using a fundamental crystal. Input frequencies at
the low end is limited to above 6.26MHz due to minimum
VCO frequency of 400MHz.
Using the FOUT equation, it is very easy to determine
what M and N values must be for a certain multiplication
factor.
FXTAL
8
M
N
FOUT =
×
FXTAL
8
1
Step Size =
×
N
FXTAL
FVCO =
×M
8
where
FXTAL is the crystal frequency or input reference frequency
M is the VCO frequency multiplier (from 128 to 511)
N is the post divider (1,2,4,8, or 16)
FVCO is the VCO frequency (400MHz to 950MHz)
3
APPLICATION NOTE
AN-07
Micrel
+5V
+5V
Zo
PECL
SY89429/30V
Input
R=Zo
R=Zo
+5V
0.1µF
3V
3V Reg.
<<Zo
+5V
+5V
Zo
PECL
Input
SY89429/30V
+5V
R=Zo
R=Zo
0.1µF
R=2Zo
+5V
R=5/3Zo
R=5/3Z
+5V
+5V
Zo
PECL
Input
SY89429/30V
R=5/2Zo
R=5/2Zo
Figure 1. Matched Impedance Termination Schemes for 5V Systems
4
APPLICATION NOTE
AN-07
Micrel
+3.3V
+3.3V
Zo=100Ω
PECL
SY89429/30V
Inputs
100Ω
100Ω
+3.3V
+3.3V
Zo
PECL
Inputs
SY89429/30V
+3.3V
0.1µF
R=Zo
R=Zo
R=Zo
+3.3V
+3.3V
+3.3V
Zo
R=5/2Zo
R=5/3Zo
R=5/2Zo
PECL
SY89429/30V
Inputs
R=5/3Zo
Figure 2. Matched Impedance Termination Schemes for 3.3V Systems
5
APPLICATION NOTE
AN-07
Micrel
XTAL2
XTAL1
16MHz
Figure 3a. Recommended External Components for Crystal Oscillator
LOOP_FILTER
LOOP_REF
3300pF
0.47µF
150Ω
Figure 3b. Recommended Passive Filter Circuit
6
APPLICATION NOTE
AN-07
Micrel
Figure 4. Power Supply Filtering
7
APPLICATION NOTE
AN-07
Micrel
ECL
VCC
FOUT
SY89429/30V
ECL
ELT23
ELT23L
TTL
Input
GND
–3.3V
–5.2V
Figure 5. Interfacing to SY89429/30V TTL Inputs with
ECL Signals for True ECL Designs
MICREL-SYNERGY 3250 SCOTT BOULEVARD SANTA CLARA CA 95054 USA
TEL + 1 (408) 980-9191 FAX + 1 (408) 914-7878 WEB http://www.micrel.com
This information is believed to be accurate and reliable, however no responsibility is assumed by Micrel for its use nor for any infringement of patents or
other rights of third parties resulting from its use. No license is granted by implication or otherwise under any patent or patent right of Micrel Inc.
© 2000 Micrel Incorporated
8
相关型号：
©2020 ICPDF网 联系我们和版权申明