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Anahtarlı-Kapasitör tekniği ile IIR/FIR ve N-yollu filtrelerin gerçeklenmesi

Realization of IIR/FIR and N-Path filters using switched-capacitor techniques

  1. Tez No: 22076
  2. Yazar: SABRİ DİZMEN
  3. Danışmanlar: PROF. DR. FUAT ANDAY
  4. Tez Türü: Yüksek Lisans
  5. Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
  6. Anahtar Kelimeler: Anahtarlı kapasite devreleri, Filtreler, Switched capacity circuits, Filters
  7. Yıl: 1992
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: Belirtilmemiş.

Özet

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Özet (Çeviri)

capacitances. Now, while the value of a MOS capacitor can only be controlled with an accuracy of 5-10 percent, the ratio of two capacitances can be made accurate to within a fraction of 1 percent. Hence, an accuracy of 0.1-0.5 percent is achievable for the time constant. This is because most error sources affect capacitors on the same chip (especially those located close to each other) the same way. This tracking behavior extends to variations with temperature and aging. The area requirement for resistors is also drasti cally reduced by using the equivalent branches. For the value R=10 Q quoted above, assuming a 100kHz clock fre quency, by (2) a switched capacitor of value C=lpF is required. The area occupied is thus about 3mil2 (the area of the switches is negligible) rather than 1600mil2 a reduction by a factor of 500 1 Shortly monolithic switched-capacitor (SO circuits [33 in MOS technology have been widely applied to analog signal processing with a good accuracy and less chip area. Most SC circuits are based on the SC integrator, altought it has certain limits in realizing analog func tions C4,53. Recently, SC dif f eretiators have been developed and various applications have been explored [63 It is found that many circuits which are not realizable in conventional SC integrators can be implemented by SC differentiators. With both SC differentiators and integrators, therefore, the application field of SC cir cuits can be extended and their design versatility can be enhanced. Recently, monolithic inverting and noninverting SC differentiators have been proposed and their noise per formance has been analyzed and investigated. It is shown that the SC differentiators have simple structures and are stray insensitive. In addition, they have a good noise performance and is compatible in both fabri cation technology and operation with conventional SC integrators. It is expected that the proposed SC differentiator can be applied to design useful SC cir cuits and systems. There are two interesting applications of SC cir cuits. One is the realization of discrete-time trans fer functions in both infinite-impulse-response (IIR) and f inite-irapulse-response (FIR) forms. The other is the realization of multiplexed filter banks and N-path filters..vii-SUMMARY REALIZATION OF IIR/FIR AND N-PATH FILTERS USING SWITCHED-CAPACITOR TECHNIQUES The practical use of switched- capacitor integrated circuits began on a major scale about fifteen years ago. During this interval, many commercial integrated cir cuits utilizing switched- capacitor (SO techniques have been fabricated and marketed. High- quality analog filters had been historically realized as passive LCR circuits. Since inductors are physically large, electrically lossy and noisy, and unsuitable for miniaturization, an effort to replace them by active elements had begun in the 1960» s. The resulting circuits were the active- RC filters which gained wide acceptance over the past 30 years. To reduce their sizes, they are often realized in a hybrid construction, with monolithic op- amps and chip capaci tors soldered on a board containing thick- film resistors. The next step in miniaturization was to realize fully integrated filters CIS. Since the MOS technology offers high- quality capacitors, low leakage charge stor age, offset- free switches, and nondestructive charge sensing, it is usually preferred to bipolar technology for filtering applications. The straightforward inte gration of an active- RC filter, however, leads to difficulties. Since for an oxide thickness of 700a a lpF capacitor requires about 3mil2 (or about £000/umz) chip area, MOS capacitors aire seldom made larger than about lOOpF. Since integrated filters are commonly used in the voice- frequency (O- to 4kHz) range, they require time constants of the order RC«slO~*s. Even for a large capacitor (say, C=10pF), this requires a resistor of order 10 Ci. Such a resistor, made by using a polysili- con line or diffusion region, occupies an area around 1600milz*10°jum2, or nearly 10 percent of the average chip area of an analog MOS integrated circuit. In addi tion, MOS resistors tend to be nonlinear. -v-SUMMARY REALIZATION OF IIR/FIR AND N-PATH FILTERS USING SWITCHED-CAPACITOR TECHNIQUES The practical use of switched- capacitor integrated circuits began on a major scale about fifteen years ago. During this interval, many commercial integrated cir cuits utilizing switched- capacitor (SO techniques have been fabricated and marketed. High- quality analog filters had been historically realized as passive LCR circuits. Since inductors are physically large, electrically lossy and noisy, and unsuitable for miniaturization, an effort to replace them by active elements had begun in the 1960» s. The resulting circuits were the active- RC filters which gained wide acceptance over the past 30 years. To reduce their sizes, they are often realized in a hybrid construction, with monolithic op- amps and chip capaci tors soldered on a board containing thick- film resistors. The next step in miniaturization was to realize fully integrated filters CIS. Since the MOS technology offers high- quality capacitors, low leakage charge stor age, offset- free switches, and nondestructive charge sensing, it is usually preferred to bipolar technology for filtering applications. The straightforward inte gration of an active- RC filter, however, leads to difficulties. Since for an oxide thickness of 700a a lpF capacitor requires about 3mil2 (or about £000/umz) chip area, MOS capacitors aire seldom made larger than about lOOpF. Since integrated filters are commonly used in the voice- frequency (O- to 4kHz) range, they require time constants of the order RC«slO~*s. Even for a large capacitor (say, C=10pF), this requires a resistor of order 10 Ci. Such a resistor, made by using a polysili- con line or diffusion region, occupies an area around 1600milz*10°jum2, or nearly 10 percent of the average chip area of an analog MOS integrated circuit. In addi tion, MOS resistors tend to be nonlinear. -v-transfer function. Then the z- domain transfer function of the circuit is generated and compared to the speci fied one. Finally, capacitor values of the SC circuit can be determined to satisfy the specified z-dornain transfer function. It is difficult, however to use the proposed SC structure to implement a high- order ZIR filter <n>£) ESD. The second method proposed by Davis and Smith £31 relies on the synthetic division. By using this method, SC circuits can be constructed efficiently and direct ly from z- domain specifications. This method is a good design skill for SC circuits because the design proce dure is clear and easy. This method is also applicable for SC differentiators. Two canonical structures are proposed for the realization of IIR transfer functions using SC differentiators and the synthetic division technique. In the proposed realization method, the differentiator type of the element <z-1-l) is used instead of the <z *) element. The resultant SC IIR filters have shown the superiority over the conventional structures using <z~ ) or integrator type in component sensitivity. They can also retain the advantages of SC differentiators, such as simple structure, stray insen sitive, low sensitivity to offset voltage and power supply variations, and good noise performance at low frequency. Generally, a FIR filter can not be directly imple mented by SC integrators. Although there are many proposed structures which use delta modulation, digital storage elements and improved integrators, in this paper SC differentiators are used directly to implement FIR filters. The resultant FIR filters have a concise and simple structure with a low component and coefficient sensitivity. Direct use of SC differentiators also makes the SC FIR filters retain the advantageous fea tures of SC differentiators. The multiplexed filter banks and N-path filters have the commen advantages of using less op amps and thus may save the chip area and dc power consumption in some voice- band applications. In addition, the N- path filters can solve the narrow- band problem. In this work, the proposed SC integrators and differen tiators are applied to realize the multiplexed filter banks and N- path circuits. The second section, includes a brief instruction on transformation methods and active- SC circuits as building- blocks. Switched- capacitor filters are sampled- data circuits, with analog signal representa tion. Hence, their analysis requires, in general, the mathematical tools of both analog signals (Laplace and Courier transformations) and those of sampled signals - viii-z- transformation). Furthermore, the relations between hese two groups of transformations must be correctly ormulated and used. For these reasons, this section ives a summary of the basic definitions of analog, igital, and sampled- analog systems. Then, active-SC ntegrator and active- SC differentiator circuits are epicted and the transfer functions of these circuits re given. find also two types (BDI and FDD of active- C integrator are described. In addition, a basic delay 'lement is also given. The third section deals with design principles, ransfer functions, block diagrams and actual circuits if SC integrator and SC differentiator filters. Two ifferent filter types are discussed. These are IIR/FIR nd N- path filter forms. Also synthetic division, which s used for transforming the transfer function H(z> or Kz"1) to H<z-1- 1) is shown with an example. In the fourth section, nonideal effects in witched- capacitor circuits are discussed at first. It s known that, switched- capacitor circuits are usually ntriate systems containing many components and multiple eedback loops, and are realized normally in a fully ntegrated form. fls a result of the integrated real- zat ion, many an avoidable parasitic effects, noise and lement variations occur in these circuits. These ffects and precautions are shown in this section. Then, any examples of the different design techniques and nd different types are given. -lx-

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