| The proliferation of digital computing and signal processing in electronic products has often been described as "the world is becoming more and more digital". Compared with the analog circuit, it has many advantages: the digital circuit is less sensitive to the interference, the requiring accuracy of the power supply and the change of process is smaller. So that the design is more simple, with a stronger programmability.All naturally occurring signals, however, are analog signals. Therefore, it needs digital devices to interact with the analog world. "The world is becomeing more and more digital", which means that it is necessary to have more connections between the analog world and digital processing devices. These devices are usually called analog to digital converters(ADC). ADC can be used in many electronic devices, for example, in mobile phone for voice coding, in the digital camera for signal coding of the image sensor, in telephone modem system for input signal coding.The type of ADC are varied. According to the different sampling frequency, ADC is divided into two categories: traditional nyquist ADC and oversampled ADC. The most typical oversampled ADC is Sigma Delta ADC. Compared with traditional ADC, Sigma Delta ADC can obtain higher precision with lower hardware consumption, and is widely used in advanced audio fields and others.In this paper, according to the design specifications, we discussed all kinds of modulator structure and selected the appropriate modulator parameters,finally we decided to adopt a feedforward structure with 5th order, 1.5bit quantization, the sampling rate is 32 OSR. By Simulink modeling in Matlab, design requirements has been met. Sub circuit including amplifier, a quantizer, a two phase non-overlapping clock, an adder circuit have been achieved in Cadence, and then we built the whole circuit of modulator, the requirement of the performance has been satisfied: the signal to noise ratio(SNDR) for 100.99 d B, effective precision ENOB 16.48 bit. |
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