说明：  该文件中是关于一些VHDL许多编程实例以及源码分析，希望对VHDL爱好者有用。卷4包括低频数字相位测量仪、电压控制LC振荡器
(The document is on a number of VHDL source code in many programming examples and analysis, in the hope that useful VHDL enthusiasts. Volume 4, including the low-frequency digital phase-measuring instrument, voltage-controlled LC oscillator)