VCO(压控振荡器)是一种模拟电路,所以在数字可编程芯片设计库中找不到VCO。当需要用这种电路来实现同步或时钟频率倍增时,必须找到一种可与标准数字功能元件(如“与”门和“与非”门)一起使用的电路。制作可变频率振荡器的方法有好几种。例如,你可以用变容二极管来改变振荡器频率。遗憾的是,这种变容二极管的每伏频率的变化量很小。所以,采用一个倒相器和几只电容器的标准皮尔斯振荡器不适用于这样的场合。另一种方法是使用一个施密特触发器倒相器和改变充电的电阻器。这种方法可能适用,但该IC滞后性的容差通常很大,所以选用的倒相器芯片会对频率产生很 The VCO (Voltage Controlled Oscillator) is an analog circuit, so a VCO can not be found in a digital programmable chip design library. When this type of circuit is needed to achieve synchronization or clock frequency multiplication, a circuit must be found that can be used with standard digital functions such as AND gates and NAND gates. There are several ways to make a variable frequency oscillator. For example, you can use a varactor to change the oscillator frequency. Unfortunately, this varactor diode has a small change in frequency per volt. Therefore, a standard Pierce oscillator with one inverter and several capacitors is not suitable for such applications. Another way is to use a Schmitt trigger inverter and change the charging resistor. This method may be applicable, but the IC’s hysteresis tolerance is usually very large, so the choice of the inverter chip will produce a very frequency