请教ADC中T/H电路的FFT SNR仿真

meidinlei

我是用Hspice跑tran然后将print出来，导入Matlab做FFT
比如sampling frequency fs=150M, tran的仿真精度设为 1/fs/8，
但是tran仿真采用的是变化步长，这样的结果如何去做FFT?
通常的作法是怎样的?
望达人指教!

meidinlei

你是说在sp仿真文件里写一堆.meas语句么
如果我要采1024个点那不是要写1024行measure语句？每个采样时间点都差一个采样周期
能否在Hspice仿真的时候设置为不变时间步长呢？这样可以在Matlab里面将所需要的数据直接提取出来。
我没有在user guide中发现怎么设置

prof3

Yes, 要写1024行measure语句,每个采样时间点都差一个采样周期,Then FFT,
You can use Perl to automatically do the job. Very simple.

meidinlei

谢谢大家！
看来这是最直接的办法了。

duling653

HSPICE可以直接做FFT啊, 为什么要用MATLAB呢

meidinlei

T/H保持后的的信号是我们关心的，而不是包括之前tracking的信号，如果直接fft会有差别
提取出来以后在matlab中处理可以更详细方便地提取信号，噪声以及各谐波功率

meidinlei

谢谢。多亏prof3兄提示了一下我才明白。

% generate the measure for hspice simulation
tstart=0.9; % start time to measure i.e., 0.9*(1/fs)
t(1:N)=0;
for i=1:1:N
    t(i)=(tstart+(i-1))*(1/fcs);
    disp(['.measure tran vout_',int2str(i),' find v(out) at=',num2str(t(i))]);
end

meidinlei

.measure tran vout_1 find v(out) at=6e-009
.measure tran vout_2 find v(out) at=1.2667e-008
.measure tran vout_3 find v(out) at=1.9333e-008
.measure tran vout_4 find v(out) at=2.6e-008
.measure tran vout_5 find v(out) at=3.2667e-008
.measure tran vout_6 find v(out) at=3.9333e-008
.measure tran vout_7 find v(out) at=4.6e-008
.measure tran vout_8 find v(out) at=5.2667e-008
.measure tran vout_9 find v(out) at=5.9333e-008
.measure tran vout_10 find v(out) at=6.6e-008
.measure tran vout_11 find v(out) at=7.2667e-008
.measure tran vout_12 find v(out) at=7.9334e-008
.measure tran vout_13 find v(out) at=8.6e-008
.measure tran vout_14 find v(out) at=9.2667e-008
.measure tran vout_15 find v(out) at=9.9334e-008
。。。。

prof3

Great. Likely, you can get the Digital Output from Spice Simulation then FFT. This is a very helpful methods when you doing ADC simulation.
Since now your FFT script is done by yourself, you can easily modify what you want and since now the data is very small, your operation is very fast. You don't need to wait a long time to process the whole waveform data, just like stupid Cadence does.

Industry ADC design and simulation in most world class company like Broadcom, MediaTek, Marvell, SiliconLab etc using similar approaches.

duling653

10楼所measure的点是不是都是每次保持建立好之后的点?