Lossy Transmission Line Filters

Reactive bandpass and low-pass filters often exhibit spurious responses in the frequency region above the design passband. The spurious responses limit the effectiveness of the filter in preventing interference by out-of-band signals. A simple and inexpensive technique for reducing or eliminating these passbands is to add short sections of an appropriate lossy transmission line in series with the conventional filter. A significant size reduction of conventional transmission line reactive filters can also be realized along with the reduction or elimination of spurious passbands by combining a lossy dielectric with the conventional reactive elements. This paper discusses the application of lossy line filters in cascade with and integrated into conventional reactive filters. The design of lossy transmission line sections and wide-band impedance matching techniques are described.     

Tables of Element Values for the Distributed Low-Pass Prototype Filter

An exact general synthesis for the distributed stepped-impedance low-pass prototype filter is presented here. Tables of values of the step impedances of filters having Chebyshev equal-ripple characteristics are given for up to 21 elements over a wide range of bandwidths and ripple levels. The tables are usefuf for the design of short-line low-pass filters, direct-coupled cavity filters, stepped-impedance acoustic or optical filters, impedance transformers, and branched guide directional couplers, as described in the papers of L. Young.     

A real-time programmable switched-capacitor filter

Four independent real-time programmable switched-capacitor filters have been fabricated on a single NMOS chip. The filters are second-order sections with digitally programmable Q and center frequency. Either low-pass or bandpass functions are available by selecting the appropriate input. The device is microprocessor compatible and includes permanent programming capability as well as an on-chip oscillator. The circuit implementation, programming capability, and operation are described.     

Tapered Corrugated Waveguide Low-pass Filters

Several new synthesis techniques are described for the design of tapered corrugated waveguide low-pass filters. Previous techniques are based on image-parameter methods which are both nonoptimum and difficult to apply to new specifications. The new synthesis methods give filters which can be constructed to work directly from dimensions generated by a computer. The impedance tapering implies that the terminating impedance transformers used in the image-parameter designs may be either eliminated or reduced in length.     

Exact Design of TEM Microwave Networks Using Quarter-Wave Lines

Modem network theory procedures, based on Ozaki-Ishii synthesis techniques, are reviewed for application in the design of TEM mode microwave networks using parallel coupled bars and/or series and shunt stubs. The circuit equivalences and identities obtained are theoretically valid over the entire frequency spectrum and lead to several physical configurations having identical response functions. These equivalent circuits often allow simplification of the physicrd circuitry and realization of both broad and narrow bandwidths. The problem of practical circuit configurations is discussed from the viewpoint of bandwidth and circuit element values. Neglecting multiple responses, TEM low-pass, high-pass and band-pass butterworth filters are shown to offer steeper bandedge characteristics than those of corresponding lumped element filters. The use of complementary filters to match a source and load over a wide frequency range is outlined and TEM realizations of these complements are obtained. A simple procedure for obtaining element values of butterworth complements is described. An analysis of parallel coupled filters is made and a simplified equivalent circuit is obtained. An exact synthesis procedure for parallel coupled bar filters and their equivalent forms is given. Construction details and experimental results are described for two filters which use series stubs.     

Design of Wide-Band (and Narrow-Band) Band-Pass Microwave Filters on the Insertion Loss Basis

A method for design of band-pass microwave filters is described that combines the image and insertion-loss points of view to give an approximate design method having simplicity, but also high precision. This method is applicable for filter designs ranging from narrow to very wide bandwidths (2 to 1 or more). The desired insertion loss characteristic is obtained by use of a lumped-element, Tchebycheff, or maximally flat (or other) low-pass prototype. With the aid of the concept of impedance inverters, the prototype is converted into a cascade of symmetrical (but differing) sections. The image properties of symmetrical sections of the band-pass microwave filter structure are then related to those of corresponding sections of the prototype. Straightforward design equations are given for filters using short-circuited or open-circuited stubs, and also for filters using parallel-coupled lines. Mapping functions are derived that permit accurate prediction of the microwave filter cutoff characteristic from that of the prototype. The responses of a number of filter designs were computed, and a Tchebycheff filter with a 2.2 to 1 band-width was built and tested. The reponses of all of the filter designs were in close agreement with the prescribed characteristics, and the accuracy of the mapping functions was verified.     

Systematic Method for the Exact Synthesis of Ultra-Wideband Filtering Responses Using High-Pass and Low-Pass Sections

A systematic consistent and analytical method for the exact synthesis of ultra-wideband bandpass filtering responses using the isolated cascade connection of high- and low-pass sections is presented in this paper. Through the described synthesis technique, the optimum values for the design parameters of the high- and low-pass sections are computed from the initial specifications of the intended bandpass filtering profile. The theoretical results are validated with a synthesis example for both the Butterworth and Chebyshev cases. Furthermore, to prove the practical viability of the ultra-wideband filter topology based on high- and low-pass sections, a prototype at 4 GHz is designed, constructed in hybrid technology, and characterized. The main advantages of this wideband microwave bandpass filter solution are also highlighted.     

Filters with Single Transmission Zeros at Real or Imaginary Frequencies

A new unified theory is presented for the synthesis of exactly equiripple low-pass prototypes having: a) one simple pole of attenuation at a real frequency; or b) a single pair of real-axis transmission zeros (giving linear-phase performance). These types of filters may be regarded as representing the least possible degree of complication over the conventional Chebyshev filter, and are usually realized with one extra cross coupling in the structure. It is demonstrated that this gives much improved skirt selectivity in the case of a finite frequency pole, making it a viable intermediate case between the Chebyshev and elliptic function filters, while in the case of real-frequency zeros, very flat group delay over 50 percent of the passband is achieved with minimal cost in insertion loss and skirt rejection. Approximate and exact synthesis techniques are described, including results for the previously neglected odd-degree case. Experimental results demonstrate agreement with theory.     

Quasi-static design technique for MM-wave micromachined filterswith lumped elements and series stubs

This paper describes micromachined, membrane-supported low-pass and bandpass filters which are suitable for microwave and millimeter-wave (MM-wave) application. The designs are realized in coplanar-waveguide (CPW) form using short- and open-end series stubs with integrated metal-insulator-metal (MIM) capacitors, and are compact in lateral and longitudinal dimensions. A computationally efficient analysis has been developed for the design and characterization of the filters. The technique is based on a quasi-static coupled-line (CL) treatment of the series stubs, and uses normal mode impedance parameters, which are calculated with the spectral-domain approach (SDA). Due to the broad TEM-bandwidth of the membrane-supported transmission lines, the method can accurately predict filter responses well into the rejection band. To demonstrate the above claims, the measured and simulated S-parameters of a 0.3 mm ×2.2 mm low-pass filter with a cutoff frequency at 17 GHz, and a second passband at 115 GHz, are presented. The new approach is also used in the design of bandpass filters which exhibit 1.5-2-dB insertion loss and bandwidths around 10%     

Microstrip bandpass filters on substrates with high permittivities

A new class of compact microstrip bandpass filters, the stepped-impedance resonators of which are located close together at a gap of 0.1–0.2 mm, is described. Basic two- and three-element sections of microstrip filters, which are designed around stepped-impedance impedance resonators used to implement tiny selective devices with overall sizes and characteristics comparable to those of microwave ceramic filters, are proposed. It is justified that the mentioned filters can be equipped with closely neighboring metallic shields whose heights are equal to the substrate thickness. As a consequence, these filters turn out to be thinner. The frequency responses of experimental microstrip filters operating at frequencies of 1.75–2 GHz and manufactured on the 1-mm-thick substrates with the permittivity ɛ _r = 100 have been analyzed. The three-pole microstrip filter with a shield (its operating frequency is 1.96 GHz, and sizes are 5 × 5 × 1.5 mm) has been simulated. It is demonstrated that new microstrip filters can be competitive with low-sized ceramic filters in certain applications.     

Small Elliptic-Function Low-Pass Filters and Other Applications of Microwave C Sections

A type of elliptic-function low-pass filter that is easy to design and construct, has low passband loss, and is very compact is described. With simple scaling and a limited number of standard parts, a broad range of cutoff frequencies can be obtained. Experimental results are presented for three filters with cutoff frequencies of 0.75, 1.0, and 1.5 GHz. Each filter occupies a volume of about 0.5 in/sup 3/. A physical interpretation of the conventional scaling transformation S =S'/ /spl Omega//sub c/' is given for networks containing unit elements. Use of this transformation is shown to yield scaled networks containing microwave C sections rather than unit elements. Applications to broad-band impedance transformers are given and other possible applications are suggested.     

A low-power NMOS transmit/receive IC filter for PCM telephony

A very low-power single chip NMOS implementation of the transmit and receive PCM filters used in telephony applications is described. The circuit utilizes doubly-terminated switched capacitor low-pass and high-pass filters and meets accepted requirements without trimming. The filters have low idle-channel noise, consume only 20 mW of power, and are realized in a small area of silicon. Design of the overall architecture, the individual filter sections, and the operational amplifiers in NMOS technology is described.     

Stepped-Impedance Transformers and Filter Prototypes

Quarter-wave transformers are widely used to obtain an impedance match within a specified tolerance between two lines of different characteristic impedances over a specified frequency band. This paper gives design formulas and extensive tables of designs, most of which were especially derived so that an integrated account could be presented for the first time. Numerous examples are given. Only homogeneous, synchronous transformers and filters are included in this paper, but a short bibliography on related topics is appended. The theory is also applied to band-pass filters, by showing how to convert quarter-wave transformers into half-wave filter prototypes. The theoretical and numerical results presented are applicable to the design of impedance transformers, direct-coupled cavity filters, short-line low-pass filters, optical antireflection coatings and interference filters, acoustical transformers, branch-guide directional couplers, TEM-mode coupled-transmission-line directional couplers, and other circuits. These applications have been or will be dealt with in separate papers; this paper gives the basic theory and some of the numerical data required for these applications.     

A prototype switched-capacitor voltage-wave filter realized in NMOS technology

Presents a novel approach to the realization of monolithic filters. The method is based on using sampled analog signals and is related to the wave digital filter in its design techniques. The eventual monolithic realization in NMOS technology is in the form of a switched-capacitor structure. The design is exact and there is no requirement for a high relative clock frequency. Only unity-gain buffers are required, as opposed to high-gain differential-input operational amplifiers, and so the technique is well suited to CMOS technology. Performance is determined by capacitance ratios and the design is optimally insensitive to parameter variations. Capacitance ratios are moderate relative to those encountered in existing switched-capacitor filters. Results are presented for a prototype integrated circuit design containing fifth- and seventh-order low-pass Chebyshev filters with a designed cutoff at one-eighth clock frequency. The responses achieved for the prototype design show excellent agreement with the theory.     

PCM编解码器中高性能开关电容滤波器设计

基于PCM(Pulse-Code-Modulation, 脉冲编码调制)语音编解码器设计了其中的发送端开关电容滤波器,包括高通滤波器和低通滤波器.对高通滤波器和低通滤波器的设计分别采用两种不同的方法--级联法和梯形法,然后把这两部分级联起来就实现了带通滤波器.仿真结果表明开关电容带通滤波器通带波纹0.24 dB,阻带衰减37 dB,对60 Hz以下频率的衰减大于32 dB,动态范围达到90 dB,满足D4信道处理单元发送滤波器的技术要求[1].设计的开关电容滤波器在一款PCM语音编解码芯片中成功实现.     

A Harmonic Rejection Filter Designed by an Exact Method

An exact design procedure for band-stop filters is used to design a transmission-line filter with one point of perfect match at a fundamental frequency and one point of infinite attenuation at a harmonic frequency. This design method is based on the mapping of the response of a low-pass prototype into that of a transmission line filter. Here a three-element Chebyshev filter is chosen as the prototype and the otherwise general procedure is adapted for the special case of rejection of the second harmonic.     

Approximate small-signal analysis of the series and the parallelresonant converters

Approximate transfer functions of series and parallel resonant converters are given which are in good agreement with the results of exact analysis as well as the results of experiments. It is shown that the dominant behavior of these transfer functions is determined by the output low-pass filter modified by the internal impedance of the converter. The high-frequency behavior, on the other hand, is given by a second-order response whose frequency is at the difference between the resonant and the switching frequencies and whose Q is the original resonant Q modified by the internal impedance of the converter     

Low-pass and high-pass filters using coaxial-type dielectric resonators

This paper proposes new low-pass and high-pass filters using coaxial-type dielectric resonators. The low-pass filter has a LC-type circuit structure and is composed of three inductances and two resonance circuits. The resonance circuits are the open-ended coaxial-type dielectric resonators whose length is λg/4. The high-pass filter has a CL-type circuit structure. Two high-pass filters are described, one of them is composed of three capacitances andtwo resonance circuits, the other is composed of five capacitances and four resonance circuits. The operating frequency range of the low-pass filter is 0.13–0.9 GHz and the cutoffency is 900 MHz, and the insertion loss is 0.3 dB. The corresponding quantities of the high-pass filter are 0.9–2.5 GHz, 900 MHz, and 0.3 dB, respectively.     

In-Line Waveguide Selective Linear Phase Filters

A procedure is described whereby narrow-band waveguide selective linear phase filters may be designed from a low-pass prototype linear phase network. The structure is comprised of a cascade connection of basic sections, each containing a direct-coupled cavity together with a dual-mode resonator. Each dual-mode resonator takes the form of a square guide mounted on the broad wall of the main rectangular guide and coupled to this guide by a small aperture. Explicit formulas for the susceptance of the coupling apertures and electrical lengths of the cavities are given in terms of the low-pass prototype.     

Voltage-mode first-order universal filter realizations based on subtractors

Two new voltage-mode (VM) first-order universal filters including two subtractors as active elements as well as one resistor and one capacitor (grounded) as passive components are proposed in this paper. Each of the proposed first-order universal filters can realize low-pass response, high-pass response with a low output impedance and all-pass response with a low output impedance simultaneously. As a result, each of them can be connected to any other VM structures easily. Neither of them suffers from passive element matching conditions. They are free from non-ideal current gains which are frequency dependent. Nevertheless, each of them does not have the feature of high input impedance. A lot of simulations where 0.13 µm IBM CMOS technology parameters are used are carried out through SPICE program. The power supply voltages of the subtractors are chosen as ±0.75 V. Each of the proposed first-order universal filters dissipates 1.77 mW. Furthermore, an experimental test is accomplished so as to show the performance of the first proposed first-order universal filter as an example.