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Nt1330 Unit 1 Lab Report

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In this section we first briefly explain the properties of a first-order Delta Sigma modulated bit-stream. Based on these properties, we propose the P-N pair method to process the Delta Sigma modulated bit-streams.

A Delta Sigma modulator converts an analog input signal to a Delta Sigma modulated digital bit-stream. A first-order Delta Sigma modulator consists of an analog integrator, a one-bit ADC, and a one-bit digital to analog converter (DAC), as shown in Fig. 2. In the Delta Sigma modulator circuit, the analog input port and the digital output port can use either dual power supplies or a single power supply. To avoid confusion, we use P and N to represent the polarity of the output digital signals. P means a digital positive value “true", while N means a digital negative value “false". We use numbers to represent digital or analog levels. For example, −1 and +1 represent the dual power supply level VSS and VDD, respectively. 0 means analog ground, which is 0 volts in a dual power system. …show more content…

When the input is positive, the digital output bit-stream contains more P bits than N bits. There can be consecutive P bits, but each N bit is separated by at least one P bit. Thus, there are no adjacent N bits when the input is positive. Similarly, when the input is negative, the output bit-stream consists of single P bits separated by one or more N bits. A Delta Sigma bit-stream toggles equally between N bits and P bits when its analog value is 0. Delta Sigma modulation is a type of Pulse Density Modulation (PDM), which means the output digital bit-stream can be converted back to an analog value using a digital moving-average filter. Therefore, in a Delta Sigma modulated bit sequence ai, which has a total of W bits, if there are n bits having the value N, and p bits having the value P, then the analog value y of this bit sequence can be written

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