TI中文支持网尊敬的Ti公司及各位同行：
我用的是DDC112，通过stm32F1单片机的PWM功能产生两个时钟：第一个是clk时钟，频率12MHz；第二个是CONV积分时间，可调；
第一种情况：DDC112输入端空载，我用PWM输出1000ms的积分时间方波，占空比为50%，那么DDC112工作在continue模式，我用stm32F1的SPI采集结果换算成电流为以下结果：
ch1:-58.96 ch2:-49.04fA
ch1:-37.08 ch2:-46.16fA
ch1:-58.82 ch2:-48.52fA
ch1:-37.04 ch2:-46.68fA
ch1:-58.45 ch2:-48.80fA
ch1:-35.62 ch2:-46.35fA
ch1:-57.84 ch2:-50.07fA
ch1:-33.08 ch2:-44.19fA
ch1:-58.59 ch2:-49.60fA
ch1:-34.64 ch2:-47.39fA
ch1:-58.45 ch2:-50.02fA
ch1:-33.88 ch2:-47.72fA
ch1:-58.73 ch2:-51.15fA
ch1:-33.36 ch2:-45.13fA
ch1:-57.93 ch2:-47.95fA
ch1:-56.94 ch2:-49.13fA
ch1:-35.95 ch2:-46.87fA
ch1:-58.12 ch2:-50.02fA
ch1:-37.60 ch2:-46.45fA
ch1:-59.34 ch2:-49.65fA
ch1:-35.48 ch2:-45.84fA
ch1:-59.34 ch2:-49.79fA
ch1:-35.29 ch2:-48.14fA
可以看出CH1数据有明显的台阶效应，这是为何产生的？
然后我将积分时间设置为50ms方波（占空比50%），同样空载DDC112输入（没接信号），数据如下
ch1:80.00 ch2:-137.41fA
ch1:56.47 ch2:-173.18fA
ch1:-360.47 ch2:-118.59fA
ch1:-340.71 ch2:-82.82fA
ch1:-326.59 ch2:-30.12fA
ch1:-14.12 ch2:-353.88fA
ch1:-31.06 ch2:-370.82fA
ch1:-55.53 ch2:-410.35fA
ch1:-276.71 ch2:25.41fA
ch1:-269.18 ch2:50.82fA
ch1:-275.76 ch2:76.24fA
ch1:-288.00 ch2:22.59fA
ch1:-36.71 ch2:-378.35fA
ch1:-27.29 ch2:-352.00fA
ch1:8.47 ch2:-295.53fA
ch1:8.47 ch2:-266.35fA
ch1:-356.71 ch2:-89.41fA
ch1:-373.65 ch2:-135.53fA
ch1:-375.53 ch2:-174.12fA
ch1:76.24 ch2:-130.82fA
ch1:92.24 ch2:-85.65fA
ch1:97.88 ch2:-71.53fA
ch1:-430.12 ch2:-294.59fA
ch1:-439.53 ch2:-312.47fA
ch1:-447.06 ch2:-327.53fA
ch1:-463.06 ch2:-356.71fA
ch1:137.41 ch2:24.47fA
ch1:149.65 ch2:43.29fA
ch1:139.29 ch2:39.53fA
ch1:-485.65 ch2:-427.29fA
ch1:-488.47 ch2:-429.18fA
ch1:-484.71 ch2:-417.88fA
ch1:-488.47 ch2:-443.29fA
ch1:161.88 ch2:69.65fA
ch1:160.94 ch2:54.59fA
ch1:155.29 ch2:59.29fA
ch1:-488.47 ch2:-407.53fA
ch1:-469.65 ch2:-400.94fA
ch1:-465.88 ch2:-411.29fA
ch1:-467.77 ch2:-385.88fA
ch1:154.35 ch2:45.18fA
ch1:158.12 ch2:49.88fA
ch1:165.65 ch2:25.41fA
ch1:-476.24 ch2:-373.65fA
ch1:-464.00 ch2:-354.82fA
ch1:-468.71 ch2:-354.82fA
ch1:-448.00 ch2:-353.88fA
ch1:144.94 ch2:11.29fA
ch1:134.59 ch2:18.82fA
ch1:130.82 ch2:15.06fA
ch1:-467.77 ch2:-363.29fA
ch1:-458.35 ch2:-368.00fA
ch1:-460.24 ch2:-366.12fA
ch1:136.47 ch2:-1.88fA
ch1:134.59 ch2:8.47fA
ch1:146.82 ch2:26.35fA
ch1:141.18 ch2:39.53fA
ch1:-484.71 ch2:-410.35fA
ch1:-494.12 ch2:-404.71fA
ch1:-495.06 ch2:-415.06fA
ch1:-500.71 ch2:-441.41fA
ch1:170.35 ch2:109.18fA
经过统计分析，能看出周期性波动，波动幅度很大。
请各位帮忙分析一下。
user151383853：
同样空载DDC112输入（没接信号）,可能是工频噪声的影响了.
我觉得这样的测试没有什么意义呀
liang lv：
回复 user151383853:
您好：
感谢您的回复。我又试了一下用DDC112的TEST mode进行数据采集，应该是一个积分时间有13pC。数据如下：
测试条件：积分时间10ms；range1; 数据结果单位pA：
ch1:1341.40 ch2:1341.93pAch1:1364.61 ch2:1364.79pAch1:1341.51 ch2:1341.89pAch1:1341.47 ch2:1341.97pAch1:1364.60 ch2:1364.68pAch1:1341.44 ch2:1341.88pAch1:1364.60 ch2:1364.67pAch1:1341.49 ch2:1341.97pAch1:1341.52 ch2:1341.98pAch1:1364.53 ch2:1364.69pAch1:1364.58 ch2:1364.67pAch1:1364.59 ch2:1364.79pAch1:1341.46 ch2:1341.97pAch1:1341.42 ch2:1341.89pAch1:1341.46 ch2:1341.97pAch1:1364.54 ch2:1364.80pAch1:1364.62 ch2:1364.69pAch1:1341.42 ch2:1341.98pAch1:1364.65 ch2:1364.80pAch1:1341.44 ch2:1341.99pAch1:1364.63 ch2:1364.79pAch1:1364.58 ch2:1364.68pAch1:1341.48 ch2:1342.00pAch1:1364.62 ch2:1364.67pAch1:1341.39 ch2:1341.97pAch1:1364.61 ch2:1364.67pAch1:1341.44 ch2:1341.98pAch1:1341.38 ch2:1341.99pAch1:1364.56 ch2:1364.78pAch1:1341.42 ch2:1341.98pAch1:1364.58 ch2:1364.71pAch1:1341.46 ch2:1341.94pAch1:1341.45 ch2:1341.94pA
您看仍然存在有规律的波动，这是为什么？
然后我又试了一下另外的积分时间，结果如下：
测试条件：积分时间1000ms；range1；数据结果单位fA
ch1:13628.01 ch2:13628.11fAch1:13397.00 ch2:13402.51fAch1:13628.44 ch2:13629.47fAch1:13397.80 ch2:13402.84fAch1:13627.92 ch2:13628.95fAch1:13396.72 ch2:13403.21fAch1:13628.53 ch2:13628.15fAch1:13396.58 ch2:13402.18fAch1:13627.97 ch2:13629.75fAch1:13397.10 ch2:13403.12fAch1:13628.58 ch2:13629.90fAch1:13397.85 ch2:13402.22fAch1:13627.50 ch2:13628.86fAch1:13397.00 ch2:13401.33fAch1:13627.97 ch2:13629.24fAch1:13397.52 ch2:13402.93fA
1000ms积分条件下也存在数据值交替变换的现象。我想1000ms足以平均掉50Hz工频干扰的问题了吧。
您在帮我分析一下是不是还有其它问题？
万分感谢！
Haoran Liu：
回复 liang lv:
同问，我也遇到同样的问题，测试模式下也会出现周期的波动。我使用的积分时间是0.5ms，在每个range都有。
