several high level lobes before the input signal frequency for Delta Sigma Modulator

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yangyang10182

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Hello guys,

I designed a first order delta sigma modulator in Cadence. And it is single bit. The frequency of the input signal is about 50Hz. The sampling frequency is 10KHz. I did the FFT for the output and got the spectrogram. But it looks not right. There are several lobes before 50Hz. And the signal level is much higher than the expected. I don't know what causes this problem.

I attached the spectrogram here. Hope someone can help me out. Thanks in advance!

 

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