VCO的输出频率不稳定

做了这么久的VCO还没与遇到这个问题哦

问下是怎么得到频率波形的?

It is good enough. the ripples on the frequency line are due to the mathematics calculation

是说频率那条线吗?就是calculator中的f算得啊！

thank u。通常来说不是几十kHz的范围比较是正常的吗?但是我仿出来的最大的差异达到了7，8MHz，是不是太大了?我问一些同学，他们说是我的tank里的LC设置的不合适，是这样吗?

If the simulation accuracy is not a problem, the frequency shift may be due to your LC structure.
Supposed a LC osc with a PMOS tail current source, it is well known that the operation point of the differential pair will shift from Class A mode to Class C mode. if your tank capacitor is very big, the time for the frequency fully settling is longer.

非常感谢大神指导！这么说的话，大概应该是我仿真器设置的问题，我用的是电压偏置的结构。我做的是3G到4G的振荡器，tran的仿真时间是200ns，精度设置的是10p。前段时间我的固定电容，和电阻用的都是理想的，然后换成非理想的器件，就出现了这种情况！