Akım taşıyıcı kullanarak akım transfer fonksiyonu sentezi
Current transfer function synthesis using current conveyors
- Tez No: 39280
- Danışmanlar: PROF.DR. CEVDET ACAR
- Tez Türü: Yüksek Lisans
- Konular: Bilgisayar Mühendisliği Bilimleri-Bilgisayar ve Kontrol, Computer Engineering and Computer Science and Control
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1993
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 81
Özet
ÖZET Bu tezde, farklı devre sentezi yöntemlerinden yararlanarak, ikinci kuşaktan akım taşıyıcı içeren ve akım transfer fonksiyonu gerçekleştirmeye uygun devreler önerilmiştir. önerilen yöntemleri, devre veya devre modelinin önceden seçildiği ve devre veya devre modelinin önceden seçilmediği yöntemler olarak gruplandırmak mümkündür. Ayrıştırma yönteminde devre modeli, katsayıları eşleştirme yönteminde ise devre önceden önerilmektedir. İşaret akis grafına dayanan devre sentezi yönteminde ve basamaklı tipten LC devrelerinin simülasyonu için önerilen iki metod için ise, devre veya devre modeli önce den seçilmemiştir. Ayrıca, akım taşıyıcıların idealsizlikleri incelenmiş ve bu idealsizliklerin. Önerilen devrelere ne gibi etkileri olabileceği tartışılmıştır. Akım taşıyıcı için, SPICE devre analizi programına uygun olan bir kayıplı model Önerilmiş ve bu model yardımıyla daha önce den verilmiş olan devrelerin bazılarının performansları incelenmiştir. Son olarak, akım transfer fonksiyonu gerçekleştir menin önemli bir avantajını göstermek amacıyla, bir devrenin dinamik davranışının nasıl iyileştirilebilecegi araştırılmıştır. iv
Özet (Çeviri)
SUMMARY CURRENT TRANSFER FUNCTION SYNTHESIS USING CURRENT CONVEYORS The current conveyor is a versatile active building block introduced first by Smith and Sedra in 1968. Two years later, same researchers presented a modified con veyor, second-generation current conveyor (CCI I), that have been found more useful in many applications. CCIIs are first widely used in application areas such as the realisation of controlled sources, impedance converters, impedance inverters, gyrators and various a- nalog computational elements like current amplifier, current differentiator, current integrator, current sum mer and weighted current summer. A second generation conveyor whose circuit symbol is given in figure 1, can be defined by the following hybrid equation. ly Vx İ=s (1) In this equation, + sign refers to positive conveyor that is denoted by CCII+, whereas - sign refers to ne gative one denoted by CCII-. Ix O- ? 4- O Is Figure 1 Circuit symbol of current conveyor In the last years, with the increasing awareness of vthe advantages offered by the current-mode signal pro cessing circuits, such as higher signal bandwidth with greater linearity and larger dynamic range, current con veyors are applied in the realization of these circuits in greater numbers. Second-generation current conveyor, with an input terminal y and an output terminal z which both exhibit infinite impedance, is a very convenient active element to realize current-mode as well as voltage-mode circuits like OTA (Operational Transconductance Amplifier). One of the first works on the realization of cur rent-mode active filters has been done in 1989 by Roberts and Sedra. They have proposed a new procedure, based upon the well known adjoint network concept, which enables the designer to convert any voltage-amplifier filter circuit to equivalent current-amplifier filter circuit with identical sensitivity properties. In 1991, Chang et al. have proposed a new synthe sis procedure that can be used to convert voltage-mode circuits to equivalent current-mode circuits. This met hod is based upon signal flow graph concept. After the conversion, the sensitivity properties of the circuit obtained will be equal to those of its primitive. As soon as the designers had discerned the advan tages offered by the current mode circuits including current conveyors, they tried to find out the circuits realising biquads. Many circuits have been obtained in a couple of years and have been examined. In 1990, Liu et al. have introduced a new configu ration for realizing any type of current-mode second-or der filtering transfer function with high output impe dance. This circuit employed five or six one-port pas sive RC elements. In 1991, Chang have presented two cascadable uni versal current-mode circuits with high output impedan ces. The first circuit with three outputs have employed a single negative second-generation current conveyor, three capacitors and four resistors. The second univei - sal active current filter with a single output have in cluded one resistor more than the first one. The pro posed networks with the advantages of low passive sen sitivities can supply at the output second-order lowpass vibandpass, highpass, notch and allpass current signals by- adjusting the magnitudes of capacitors and resistors. What is interresting about this two circuits is that their resonance angular frequencies and quality factors are insensitive to the tracking errors of the nonideal CCII-. In 1991, Chang et al. have introduced another uni versal active current filter with three inputs and one output. This circuit used grounded resistors and was ideal for integration. It was constructed two grounded capacitors, six grounded resistors and five CCIIs. Un like the circuit introduced in the above paragraph, this universal filter seems to be obtained using a synthesis procedure. In 1991, Liu et al. have proposed a family of cur rent-mode second-order filters suitable for the systama- tic design including five one-port passive RC elements. In this thesis, many circuits, that are designed to realize current transfer functions and obtained using well known synthesis procedures, are proposed. More over, the effects of the current conveyor nonideal it ies are studied. In the second section, the nonidealties of the cur rent conveyor operating in linear region are studied us ing well known SPICE simulator. A circuit model repre senting the nonidealities is given. Lastly, the effects of this nonidealities on a basic current-mode subcir- cuit, current amplifier, is studied using SPICE simula tor. In the third section, some circuits realizing cur rent transfer functions, are introduced. All the cir cuits are obtained using a synthesis procedure, except for the multifunction filter. In the section 3.1, the circuits, that have trans fer functions whose denominator and numerator functions can be expressed by the differences of two one-port pas sive RC networks, are presented. It is possible to show that this kind of circuits enable the designer to real ize any filter characteristics. One of this circuits obtained using this philosopy and depicted in figure 2 is studied. viiFigure 2 The circuit analysed in section 3.1 In the section 3.2, a multifunction filter, employ ing three second-generation current conveyor and six passive elements, is presented. This circuit has three outputs which supply second-order bandpass, highpass, notch or allpass current signals. By given appropriate values to the passive elements, notch or allpass filter can be obtained. It is also shown that passive sensiti vities of the pole frequency and the pole quality factor are very good. In the section 3.3, a synthesis procedure based on signal flow graph is presented and many circuits, emplo ying grounded resistors and grounded capacitors, are ob tained. It is possible to show that the sensitivity performances of this kind of circuits are good. Using this method, a variety of different circuits realizing the general biquadratic current transfer function are obtained. It is proved that a circuit realizing general nth order current transfer function can be generated. In the section 3.4, two methods to simulate LC lad der filters are given. After using both methods, the circuits obtained operates in current-mode. This means that when someone converts a passive ladder filter, that realizes a voltage transfer function, to an active fil ter using one of this two methods, the circuit derived realizes current transfer functions. The active circuit obtained employs only grounded passive elements. In the fourth section, the effects of current con veyor nonidealities in the lineer operating region are studied and it is shown that this nonidealities may cause the unstability problems. Using SPICE simulator and the circuit model given in section two, some of the viiicircuits obtained in the third section are analysed and satisfying results are obtained. In the fifth section, dynamic range of the circuits including current conveyor is studied. If the current or the voltage at the terminals of a current conveyor exceeds a certain value, current conveyor can't operate linearly. To find out the limits of the terminal sig nals, the internal circuitry of the current conveyor should be recognized. First, it is supposed that cur rent conveyor is implemented by the circuit given in figure 2.5. By analysing internal circuit, it is pos sible to find out the maximum terminal signals level not causing to clipping or slew-rate limiting effects. In this section, the dynamic range behaviour of a filter circuit obtained in section 3 is examined. It is shown that in current-mode curcuits,it is easier to adjust the voltage levels, hence it is always possible to improve dynamic range characteristic. ix
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