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| 型號： | AN-07 |
| 英文描述： | SY89429/30V Frequency Synthesis |
| 中文描述： | SY89429/30V頻率合成 |
| 文件頁數(shù)： | 1/8頁 |
| 文件大?。?/td> | 132K |
| 代理商： | AN-07 |
APPLICATION NOTE
AN-07
SY89429/30V
FREQUENCY
SYNTHESIS
Introduction
Micrel-Synergy’s SY89429/30V frequency synthesizers
are designed to be used in various clock subsystems. The
Primary function of the product is to synthesize clock
frequencies required for systems needing a high quality,
low jitter clock source.
The cost of other clock sources, either crystal or SAW
oscillators, increase dramatically as precision/frequency
requirements of digital systems push into the 100+ MHz
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.
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.
General Requirements
Operating the SY89429/30V is very simple. Very few low
cost external components are required. These low cost
external components provide the tuning capability needed
to optimize and minimize jitter characteristics in each
individual system application. To achieve the best possible
performance in jitter and power supply noise rejection, basic
high speed design guidelines should be followed.
Power Supply Requirements
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 0.1
μ
F high frequency by-pass
capacitor should be used between all separate power supply
pins and ground. V
CC1
, V
CC_QUIET
, V
CC_TTL
and V
CC_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 1
μ
F and a 0.01
μ
F 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 50
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
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 (V
CC
for a logical “1”) or a ground line (V
EE
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.
1
Rev.: E
Issue Date:
Amendment: /0
February 2000
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