Inductorless low-pass filters

High-quality inductorless lowpass filters of even degree with resistive source and load impedances can be constructed using Riordan's gyrator circuit with a modification of Bruton's method, in which the admittance of each element is multiplied by P. Some experimental results were extremely good.     

Miniature low-pass EMI filters

This paper describes miniature ceramic feedthru type electromagnetic interference (EMI) filters. Electrically, the devices function as low-pass filters with a 3-dB cutoff frequency in the low-megahertz range. The filters are mechanically rugged and in many applications can be placed in the I/O connector or substituted for the existing feedthrus. The monolithic distributed filter covered in the paper behaves as a section of transmission line at all frequencies and is essentially free of undesired resonances. The theory of lossy transmission line is used to show that with a distributed dissipative filter, the effect of terminating impedances is dramatically reduced. The effect of operating environment on the electrical characteristics is also presented.     

Design of transimpedance low-pass filters

The input of a transimpedance filter is a current signal, while its output is a voltage signal. In this article, a design method for a transimpedance filter is introduced. Also, the topologies and calculation methods of the parameters of three biquadratic transimpedance low-pass (LP) filter circuits are presented in detail, according to the value of Q which is low or medium or high. As for the high-order filter, it can be designed by transimpedance LP biquad section as first stage cascaded with voltage-mode LP filters. Finally, to verify the effectiveness of the design, a design example of a high-order transimpedance LP filter is given.     

基于分形理论的高低阻抗线低通滤波器

提出了具有分形形状的高低阻抗线低通滤波器,仿真结果表明,与传统的高低阻抗线低通滤波器相比,其通带性能得到了巨大的改善,其良好的通带性能是由于分形形状微带线的宽度阶梯渐变减弱了其电流不连续性.为了验证所提出方法的有效性,设计、加工、测量了一组不同迭代次数的分形高低阻抗线低通滤波器,结果表明,高低阻抗线低通滤波器通带内反射损耗的最大值由-17.8 dB降低到-28.6 dB,而其它性能并不因此而改变.     

Low-frequency compensation of FDNR low-pass filters

A solution to the problem of realizing an inductorless low-pass elliptic transfer function has been proposed in which grounded FDNR elements are realized. The practical bias requirements for a resistive branch to ground have resulted in nonideal low-frequency rolloff in the passband. A simple technique is proposed to prevent low-frequency rolloff, to ensure direct-coupled operation, and at the same time to satisfy the practical constraints imposed by the bias requirements of the operational amplifiers.     

Sharp-cutoff low-pass filters using floating gyrators

The practical realization in gyrator-C form of a seventh-order Cauer-parameter low-pass filter with 40-dB stopband attenuation is described. The three floating coils of the equivalent LC filter were replaced by capacitor-loaded semi-floating gyrators. The gyrators were realized in hybrid form using thick-film resistors. The performance of the filter over a temperature range from -40/spl deg/ to +61/spl deg/C was very satisfactory, without any attempt at temperature compensation being made. This, together with the wider allowable element tolerances (compared with other active RC filter methods) shows the inherent suitability of gyrator-C filters for integration. Also in this paper some of the special problems and characteristics of gyrator-C filters are theoretically discussed, in particular the realization of gyrators with floating ports, gyrator Q-enhancement, and component tolerances in gyrator-C filters.     

Log-domain high-order low-pass and band-pass filters

Continuous time current-mode high-order low-pass and band-pass filters based on the log-domain concept are presented in this paper. The passive RLC ladder networks are used as the prototype to achieve the proposed filter by simulating the RLC network synthesis method. The achieved filters have inherited the good sensitivity performance from the RLC passive prototype. Fifth-order RLC ladder low-pass filter and sixth-order RLC ladder band-pass filter are used as prototypes and the signal flow graph (SFG) technique is used for the synthesis. The SFG can identify group of integrators and several signal paths. Log-domain lossy and lossless integrators based on BJT technology are deployed to achieve the integrators for realization of proposed filters. The simulations were carried out and the results exhibited several features which are in agreement with the RLC prototype. The frequency response of filters along 100 kHz to 10 MHz can be electronically tuned through 5–500 µA of bias currents. The THD lower than 1% of LP and BP filters were measured at 10 MHz input. The multi-tone tested was included in the paper for verifying the performance of proposed LP and BP filters. The intermodulation distortions around −50 dB and −60 dB were also investigated for the proposed LP and BP filters.     

Attenuation of pulses by low-pass line filters

The attenuation of pulse-like disturbances by low-pass line filters is not strongly dependent upon the shape of the steady-state attenuation curve of the filter. The performance of such a filter as a pulse attenuator is almost uniquely determined by its 3 dB-bandwidth f₃ and by its high-frequency attenuation A _∞ . The latter quantity determines what fraction of the pulse seeps through the filter unaltered in shape. The 3 dB cut-off frequency determines the attenuation of a short pulse of duration Δ. The signal resulting from applying such a short pulse of height E to the filter has a duration of about 0.35/f₃ with a peak magnitude of E_xf₃Δ. The factor _x lies in the range 2 to 6. Pulses with a duration Δ > 0.35/f₃ arc almost unattenuated.     

Cancellation of aliasing in CCD low-pass filters

The spurious frequencies caused by aliasing in a CCD low-pass filter can be canceled in the passband by designing a prefilter into the CCDs input stage. In this paper, the authors describe how single- and multiple-stage prefilters can be used, the rejection band and attenuation being set by the number of stages. They describe the design of second-order and third-order prefilters. In a basic design, the filtering effect is obtained only around the odd multiples of clock frequency; in a more complex design, the filtering effect is also obtained around twice the clock frequency. A second-order prefilter has been integrated into the input stage of a CCD low-pass filter. Experimental results are presented.     

Design of maximally flat sharp cutoff low-pass filters

A method is given for obtaining the parameters of a maximally flat sharp cutoff low-pass filter with coincident multiple transmission zeros, which satisfies arbitrary passband and stopband specifications.     

A mixed-signal approach for tuning continuous-time low-pass filters

A mixed-signal approach for tuning the bandwidth of continuous-time low-pass filters is presented. The tuning loop uses common circuit blocks (a data converter and digital filters). Simulation results are presented for a number of filters, and measured results are presented for tuning second-order and fourth-order filters.     

Brief communication. Active-R realization of current-mode low-pass filters

An active-R realization of current-mode low-pass transfer functions is presented. Since the circuit is composed of only operational amplifiers and resistances, it is suitable for high frequency operation and monolithic IC implementation.     

On the pole locations of sharp cutoff low-pass filters

It is shown that the poles of sharp cutoff low-pass filters, Butterworth- or Chebyshev-derived, can be obtained analytically for orders 3, 4, 6, and 8, through the solution of quadratic, cubic, or quartic algebraic equations. For the Butterworth case, higher order filters having a value of 3, 4, 6, 8 for the ratio (order of filter)/(order of zero) are also shown to have analytical solutions for the poles. Explicit solutions for the Butterworth-derived filter are given for third and fourth orders.     

Resonance-free low-pass filters for the AC Josephson voltage standard

We have designed and characterized superconducting integrated circuits for the ac Josephson voltage standard that demonstrate significantly improved performance. The typical circuit consists of an array of superconductor-normal metal-superconductor Josephson junctions, which are placed in a transmission line and biased with a broad-band (dc-to-15 GHz) pulse-drive waveform. Additional low-speed (dc and audio frequency) bias and output leads contain on-chip inductors that act as low-pass filters. The operating margins of the array were improved by adding resistive shunts across these inductors to damp their intrinsic resonances. These resonances had previously degraded the integrity of the broad-band signal driving the array. We present simulations and measurements of these improved circuits that demonstrate no resonances in the range of 0.1-20 GHz. Moreover, the operating margins of the ac Josephson voltage standard were improved.     

Correction of phase-frequency characteristics of minimum-phase recursive digital low-pass filters

A technique and an example of solving the problem of PRC correction of minimum-phase recursive digital low-pass filters (RDF) have been considered using the minimax (Chebyshev) proximity criterion of approximable and approximating functions.     

Flat magnitude low-pass filters with multiple pairs of imaginary-axis zeros

It has been reported recently that if flatness at ω = 0 is not strictly required to be maximal, then a class of filters with one ripple near the passband edge and also a pair of imaginary-axis zeros can be generated. This correspondence extends the design further to the general case of multiple pairs of imaginary axis zeros.     

Derivation of low-power first-order low-pass,high-pass and all-pass filters

In this letter, a new voltage-mode (VM) configuration for providing low-power and simultaneous realization of first-order low-pass, high-pass and all-pass filters is presented. The output of the all-pass filter is taken differentially. The proposed circuit contains low number of components, i.e., only two NMOS transistors, a floating battery, a grounded capacitor and a floating resistor. Adding two NMOS transistors to the proposed circuit it is modified as an all-pass filter with a single-ended output. The main advantage of the presented circuits in comparison with other counterparts is their extremely low power dissipation. Moreover, the floating resistor can be replaced with an additional NMOS transistor in triode region to provide electronic tunability. Simulation results using SPICE program are given to demonstrate the performance of the proposed circuit.     

Flat magnitude low-pass filters with a pair of imaginary-axis zeros

It is known that the cutoff rate of a maximally flat low-pass filter can be improved either by introducing a pair of imaginary-axis zeros or relaxing the flatness condition. Making use of both techniques simultaneously, this correspondence describes how to design an nth-order low-pass filter with (n - 2) degree of flatness at ω = 0 rad/s and also including a pair of imaginary-axis zeros. Advantageous performances of the filters obtained are also described.     

Novel single-stage second-order structure for low-pass wide-band low-power continuous-time filters

A novel single-stage second-order structure for Gm-C filters is presented. It allows ample reduction in hardware and thus power consumption. Moreover, due to exploiting otherwise parasitic poles, the structure allows much higher bandwidth than in conventional designs, be achieved. To verify effectiveness of new concept, and based on the new approach to implement second-order stages, a third-order and a fifth-order continuous-time low-pass filters were implemented. The filters fabricated in a CMOS process, achieved more than 430 MHz, bandwidth and less than THD for a 400 mV_p–p 100 MHz input signal. All these accomplished with a factor of about four reduction in hardware and power. The bandwidth, output voltage swing, and dynamic range are far larger than those of any other CMOS low-pass filters thus far reported, which have bandwidth higher than 100 MHz.     

A novel cross-shape DGS applied to design ultra-wide stopband low-pass filters

This letter presents a novel low-pass filter with an ultra-wide stopband. The proposed filter is comprised of a new cross-shape defected ground structure (CSDGS). By using this structure, the filter not only supports conventional DGS performances with a sharp rejection, but also exhibits an ultra-wide stopband. For the deigned low-pass filter, an insertion loss of less than 2dB from dc to 3.5GHz and the rejection is better than 20dB from 4.3 to 15.8GHz. Predicted performances show widened and deepened stopband beyond the low passband. Furthermore, it is confirmed by measurement.