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Measurement of Delta-Sigma Converter FACULTY OF ENGINEERING AND SUSTAINABLE DEVELOPMENT . Measurement of Delta-Sigma Converter Liu Xiyang 06/2011 Bachelor’s Thesis in Electronics Bachelor’s Program in Electronics Examiner: Niclas Bjorsell Supervisor: Charles Nader 1 2 Liu Xiyang Measurement of Delta-Sigma Converter Acknowledgement Here, I would like to thank my supervisor Charles. Nader, who gave me lots of help and support. With his guidance, I could finish this thesis work. 1 Liu Xiyang Measurement of Delta-Sigma Converter Abstract With today’s technology, digital signal processing plays a major role. It is used widely in many applications. Many applications require high resolution in measured data to achieve a perfect digital processing technology. The key to achieve high resolution in digital processing systems is analog-to-digital converters. In the market, there are many types ADC for different systems. Delta-sigma converters has high resolution and expected speed because it’s special structure. The signal-to-noise-and-distortion (SINAD) and total harmonic distortion (THD) are two important parameters for delta-sigma converters. The paper will describe the theory of parameters and test method. Key words: Digital signal processing, ADC, delta-sigma converters, SINAD, THD. 2 Liu Xiyang Measurement of Delta-Sigma Converter Contents Acknowledgement................................................................................................................................... 1 Abstract ................................................................................................................................................... 2 1 Introduction ..................................................................................................................................... 1 1.1 Background: ............................................................................................................................ 1 1.2 Aim:......................................................................................................................................... 2 2 ADC Architectures.......................................................................................................................... 3 2.1 Integrating ADCs .................................................................................................................... 3 2.2 Flash ADCs ............................................................................................................................. 3 2.3 Pipelined and Subranging ADCs............................................................................................. 4 2.4 SAR ADCs .............................................................................................................................. 5 2.5 Delta-sigma ADC.................................................................................................................... 6 3 Delta-sigma ADC............................................................................................................................ 8 4 ADC parameters............................................................................................................................ 11 4.1 Total harmonic distortion (THD) .......................................................................................... 12 4.2 Signal-to-noise-and-distortion radio (SINAD)...................................................................... 13 5 ADC testing theory.........................................................................Error! Bookmark not defined. 5.1 Coherent sampling................................................................................................................. 14 5.2 Sine-wave fitting and testing method.................................................................................... 13 6 Device under test and software...................................................................................................... 16 7 Measurement methods and Evaluation.......................................................................................... 19 7.1 Data Collection and analysis ................................................................................................. 19 7.2 Parameters test function based on MATLAB ....................................................................... 20 8 Results ........................................................................................................................................... 21 9 Conclusions ................................................................................................................................... 23 10 References ................................................................................................................................... 1 11 Appendix A ................................................................................................................................. 2 3 Liu Xiyang Measurement of Delta-Sigma Converter 1 Introduction 1.1 Background As the development of multimedia technology and the third mobile communication, audio technology is used widely in our daily life. Every piece of multimedia we access on the Internet, every CD we play, every time we turn on the radio, listeners hope to have a high quality audio production. The modern communication systems are based on complicated signal processing techniques in the digital domain. The applications of digital signal processing are used widely in hi-fi audio, TV and radio, mobile phones, voice recognition and the systems which include communication and retrieval of information. Therefore, digital signal processing plays an importance role in the development of new generations of communication systems. In the real world, most signals are analog signal. The analog-to-digital conversion becomes the based part in digital signal processing. The development of Analog-to-Digital Converter (ADC) could move forward the system based on digital signal processing. So systems with good digital signal processing technology require a high resolution ADC. Nowadays, there are mainly two types ADC according to the ratio of sample frequency fs and signal bandwidth fbError! Reference source not found.: Nyquist-rate ADC and Over- sampling ADC. The digital signal is dispersed in amplitude and frequency. There are two important factors: resolution and speed for ADC. Different digital processing systems need different ADC architectures. The below Figure 1 shows the application of different types ADC[3]. In next chapter, the paper will describe the different architecture and its applications in detail. 1 Liu Xiyang Measurement of Delta-Sigma Converter Figure 1-ADC applications Therefore, it is very important to find a suitable ADC for audio applications. Nowadays, most audio measurement systems use Delta-Sigma converters for analog-to-digital conversion which is the key to improve the quality of digital audio systems. 1.2 Aim In this paper, the author wants to look for an ADC for audio applications. Describe different ADC´s architecture and applications. Then, this paper will investigate Delta-Sigma ADCs, then show how exactly each part of Delta-Sigma converter works in theory. Describe the definition and formula of Signal to Noise-And-Distortion and Total Harmonic Distortion which will be measured. Based on above theory knowledge, the paper will show a method for measurement the parameters: Signal to Noise-And-Distortion and Total Harmonic Distortion. 2 Liu Xiyang Measurement of Delta-Sigma Converter 2 ADC Architectures In the ADCs market, there are mainly five architectures. Because digital signal is dispersed in frequency and amplitude domain, there are two important factors for ADC: rate and resolution. When we choose a suitable architecture for a system, we should consider the rate and resolution of ADC. In follow sections, there are some description of five architectures. By the description, we choose Delta-Sigma converter as the best choice for audio systems. 2.1 Integrating ADCs Integrating ADCs have low speed, low cost and high resolution. The integrating architecture can avoid line frequency and noise. It converts a low bandwidth analog signal into its digital representation. An integrating ADC integrates the input signal with a digital counter. The output counter is related to the sample amplitude. Figure 2-1 shows how a dual-slope converter works [4]. The advantage is precision and nonlinearity issues because the reference voltage and sample voltage integration use the same circuit. However, such architecture has disadvantage that it need 2 N 1 clock pulses when it reaches to N-bit resolution. This type ADCs is typically applied in digital panel meters and digital multi-meters. Figure 2-1 Dual slope integrating ADC architecture [4] 2.2 Flash ADCs Flash ADCs are the fastest and most expensive converter. It uses a large number of comparator to achieve multibit conversion directly. Figure 2-2 shows a converter with N-bit resolution that has 2 N-1 comparators [3]. A change of input voltage will cause the output state 3 Liu Xiyang Measurement of Delta-Sigma Converter change in many comparators that produces a parallel N-bit output. The number of comparator is grown exponentially when the resolution is increased. The resolution of converter which is usually lower than 8 bits is limited by excessive input capacitance and power consumption because any mismatch can cause static errors [4]. This is applied in video area which need high speed conversion. Figure 2-2 Block schema of a flash ADC
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