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AD9850BRSZ 参数 Datasheet PDF下载

AD9850BRSZ图片预览
型号: AD9850BRSZ
PDF下载: 下载PDF文件 查看货源
内容描述: CMOS , 125 MHz的完整DDS频率合成器 [CMOS, 125 MHz Complete DDS Synthesizer]
分类和应用: DSP外围设备微控制器和处理器外围集成电路光电二极管数据分配系统PC时钟
文件页数/大小: 20 页 / 316 K
品牌: ADI [ ADI ]
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AD9850  
W32 = 0 W33 = 0 W34 = 1 W35 = X W36 = X W37 = X W38 = X W39 = X  
DATA (7) –  
FQ UD  
W CLK  
Figure 13. Serial Load Power-Down Sequence  
V
V
V
V
CC  
CC  
CC  
CC  
QOUT/  
QOUTB  
DIGITAL  
IN  
VINP/  
VINN  
IOUT IOUTB  
DAC Output  
Comparator Output  
Comparator Input  
Digital Inputs  
Figure 14. AD9850 I/O Equivalent Circuits  
PCB LAYOUT INFORMATION  
Analog Devices, Inc. applications engineering support is avail-  
able to answer additional questions on grounding and PCB  
layout. Call 1-800-ANALOGD or contact us at  
www.analog.com/dds.  
The AD9850/CGPCB and AD9850/FSPCB evaluation boards  
(Figures 15 through 18) represent typical implementations of the  
AD9850 and exemplify the use of high frequency/high resolution  
design and layout practices. The printed circuit board that contains  
the AD9850 should be a multilayer board that allows dedicated  
power and ground planes. The power and ground planes should  
be free of etched traces that cause discontinuities in the planes. It  
is recommended that the top layer of the multilayer board also  
contain an interspatial ground plane, which makes ground avail-  
able for surface-mount devices. If separate analog and digital  
system ground planes exist, they should be connected together at  
the AD9850 for optimum results.  
Evaluation Boards  
Two versions of evaluation boards are available for the AD9850,  
which facilitate the implementation of the device for bench-  
top analysis and serve as a reference for PCB layout. The  
AD9850/FSPCB is used in applications where the device is used  
primarily as a frequency synthesizer. This version facilitates  
connection of the AD9850’s internal D/A converter output to a  
50 spectrum analyzer input; the internal comparator on the  
AD9850 DUT is not enabled (see Figure 15 for an electrical  
schematic of AD9850/FSPCB). The AD9850/CGPCB is used  
in applications using the device in the clock generator mode. It  
connects the AD9850’s DAC output to the internal comparator  
input via a single-ended, 42 MHz low-pass, 5-pole elliptical  
filter. This model facilitates the access of the AD9850’s com-  
parator output for evaluation of the device as a frequency- and  
phase-agile clock source (see Figure 17 for an electrical sche-  
matic of AD9850/CGPCB).  
Avoid running digital lines under the device because these  
couple noise onto the die. The power supply lines to the  
AD9850 should use as large a track as possible to provide a low  
impedance path and reduce the effects of glitches on the power  
supply line. Fast switching signals like clocks should be shielded  
with ground to avoid radiating noise to other sections of the  
board. Avoid crossover of digital and analog signal paths. Traces  
on opposite sides of the board should run at right angles to each  
other. This reduces the effects of feedthrough through the cir-  
cuit board. Use microstrip techniques where possible.  
Both versions of the AD9850 evaluation board are designed to  
interface to the parallel printer port of a PC. The operating  
software runs under Microsoft® Windows® and provides a user-  
friendly and intuitive format for controlling the functionality  
and observing the performance of the device. The 3.5 inch  
floppy provided with the evaluation board contains an execut-  
able file that loads and displays the AD9850 function-selection  
screen. The evaluation board can be operated with 3.3 V or 5 V  
supplies. The evaluation boards are configured at the factory for  
an external reference clock input; if the on-board crystal clock  
source is used, remove R2.  
Good decoupling is also an important consideration. The analog  
(AVDD) and digital (DVDD) supplies to the AD9850 are  
independent and separately pinned out to minimize coupling  
between analog and digital sections of the device. All analog  
and digital supplies should be decoupled to AGND and DGND,  
respectively, with high quality ceramic capacitors. To achieve  
best performance from the decoupling capacitors, they should  
be placed as close as possible to the device, ideally right up  
against the device. In systems where a common supply is used to  
drive both the AVDD and DVDD supplies of the AD9850, it is  
recommended that the system’s AVDD supply be used.  
REV. H  
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