Integrated Sigma-Delta Data Converters: Extension and Comprehensive Application of Analog and Digital Signal Processing
It was shown in Chapter 4 that the process of conventional analog to digital conversion requires a number of high-precision operations involving band-limiting filters, samplers, quantizers and encoders. We now ask the question: is it possible to employ our knowledge of both analog and digital processors to develop an A/D converter that does not require high precision components and can be easily integrated? In particular, we know from Chapter 15 that switched-capacitor circuits have many advantages when it comes to integrated circuit implementation in MOS technology and together with digital circuits on the same chip. Can we also use switched-capacitor techniques to give an answer to this question?
It turns out that the development of switched-capacitor circuits have allowed the introduction of an ingenious method of A/D conversion that has a number of advantages over the conventional method [12, 31–35].
The general structure of the converter is shown in Figure 17.1. The high resolution is obtained by oversampling the analog input signal, that is, it is sampled at a much higher rate than the critical Nyquist rate together with a coarse quantizer that is usually a simple two-level device or a comparator, which employs feedback loops to generate a one-bit data stream.