我仿真出来的ADC 非线性过大，求帮助
我经过FFT后的SNDR，请问一下如何消除明显的凸起，是OTA引起的吗
减小OTA?开关带入噪声过大?
我设计开关是互补型，NMOS，和PMOS比列为1:1.1
首先在做SD ADC的时候要用Matlab建模，这样就可以确定目前这种谐波是否是系统环路所引入。然后对于模型中的OP引入一些非理想因素，以确认OP的参数指标，也可以看到一些谐波的大小。如果这些工作做好了，依旧有问题，那么还可以考虑其他的东西，包括开关的非线性所导致的谐波上升。当然，这个也可以建模进行仿真。总之，光有目前的一个图去猜测是不明智的，按流程逐步分析是王道。
把OPA的频宽增加，output swing也增加
In Hspice replace your OP to fully differential behavior OP (use single pole approximate ,set BW, gain, or add OP non-linearity vs signal swing). Plot the gain vs THD figure at given OP non-linear. Plot the OP non-linear vs. THD figure at given OP gain. Check your DEM algorithm if the DEM will introduce the signal dependent harmonic distorsion.
If the problem is in OP, increase OP`s (BW, gain, swing) will be helpful.
If the problem is DEM (use Matlab to check if it will introduce signal dependent harmonic), change the DEM algorithm.
Try to decrease your signal maximum level, lower the max. input defination. If the harmonic distorsion is introduced by OP, this usually help.
SDM system has many parameters, you sould build the Matlab mathematical model first to estimate the real circuit specification then start to design your circuit.