📄 直接式数字锁相环频率合成器的仿真.htm
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size=+3>数字频率合成器</FONT></B></TD>
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<TD width=704 height=246><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">作为实验，如图</SPAN><SPAN
lang=EN-US>6.5</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">所示为一个用</SPAN><SPAN
lang=EN-US>SystemView</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">实现的<A
href="http://www.mvista.com.cn/svu-www/index4/index4-4/index4-4-4.htm#image01">直接式数字锁相环频率的仿真电路</A>。为了节省仿真时间，参考振荡器直接采用了较低的</SPAN><SPAN
lang=EN-US>10Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">正弦波信号（图符</SPAN><SPAN
lang=EN-US>0</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">），而没有采用由一个较高的参考振荡器经过分频</SPAN><SPAN
lang=EN-US>R</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">得到</SPAN><SPAN
lang=EN-US>f<SUB>R</SUB></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的办法。锁相环的</SPAN><SPAN
lang=EN-US>VCO</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">用了一个</SPAN><SPAN
lang=EN-US>FM</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">图符代</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">替（图符</SPAN><SPAN
lang=EN-US>2</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">），其载波频率设置为</SPAN><SPAN
lang=EN-US>195Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，增益为</SPAN><SPAN
lang=EN-US>20Hz/V</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。环路低通滤波器使用了一个</SPAN><SPAN
lang=EN-US>8</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">极点的贝塞尔低通滤波器（图符</SPAN><SPAN
lang=EN-US>5</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">），带通为</SPAN><SPAN
lang=EN-US>5Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">。在滤波器前端加入了一个</SPAN><SPAN
lang=EN-US>100Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的采样图符以减少系统仿真时的运行时间。分频器使用通信图符库中的</SPAN><SPAN
lang=EN-US>N</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">倍分频器（图符</SPAN><SPAN
lang=EN-US>3</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">），分频器的</SPAN><SPAN
lang=EN-US>N/(N+1)</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">控制端未使用。若取分频比</SPAN><SPAN
lang=EN-US>N=20</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，则锁相环的输出</SPAN><SPAN
lang=EN-US>f<SUB>0</SUB></SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">应该锁定在</SPAN><SPAN
lang=EN-US>f<SUB>0</SUB> =</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">（</SPAN><SPAN
lang=EN-US>N</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">＋</SPAN><SPAN
lang=EN-US>1</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">）</SPAN><SPAN
lang=EN-US>f<SUB>R</SUB> =21</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">×</SPAN><SPAN
lang=EN-US>10=210Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">上，<A
href="http://www.mvista.com.cn/svu-www/index4/index4-4/index4-4-4.htm#image02">输出信号的频谱图</A>如图</SPAN><SPAN
lang=EN-US>6.6</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">所示，在</SPAN><SPAN
lang=EN-US>210Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">出有较高的能量峰值，说明输出的信号被锁定在</SPAN><SPAN
lang=EN-US>210Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">上了。将</SPAN><SPAN
lang=EN-US>N</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">改设为</SPAN><SPAN
lang=EN-US>19</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，则输出信号应该为</SPAN><SPAN
lang=EN-US>200Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，如<A
href="http://www.mvista.com.cn/svu-www/index4/index4-4/index4-4-4.htm#image03">图</A></SPAN><A
href="http://www.mvista.com.cn/svu-www/index4/index4-4/index4-4-4.htm#image03"><SPAN
lang=EN-US>6.7</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">所示</SPAN></A><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">，仿真的结果在</SPAN><SPAN
lang=EN-US>200Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">处的频谱有峰值。改变</SPAN><SPAN
lang=EN-US>N</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">为其它值，输出信号的频率将变为</SPAN><SPAN
lang=EN-US>10Hz</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的整数倍。但事实上由于锁相环的锁定范围限制（与滤波器带宽和</SPAN><SPAN
lang=EN-US>VCO</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">的载波最大变化范围有关），只能输出</SPAN><SPAN
lang=EN-US>VCO</SPAN><SPAN
style="FONT-FAMILY: 宋体; mso-ascii-font-family: 'Times New Roman'; mso-hansi-font-family: 'Times New Roman'">载波频率附近的几个整数倍的频率。</SPAN></TD>
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