VHF Filters Research Articles

A 0.25-V calibration-less inverter-based OTA for low-frequency Gm-C applications

This paper presents a calibration-less inverter-based operational transconductance amplifier (OTA) built with intrinsically matched CMOS inverters, therefore, dispensing any kind of calibration circuit. In addition, the circuit is implemented in IBM 130-nm CMOS processes using non-uniformly doped MOS transistors and is specially designed to suit low-frequency Gm-C applications such as biomedical applications. The intrinsically matched CMOS inverters design relies on the utilization of the distributed layout of halo-implanted MOS transistors operating in weak inversion. In this work we demonstrate that this technique stabilizes the switching point voltage of the CMOS inverter, reducing its statistical variation, besides allowing gain enhancement and its adjustment, which is desirable for the Gm-C design. Based on the original topology proposed by Bram Nauta (and its derivative works), focusing on the tunability of VHF filters, we adapt this topology for constant Gm applications. Moreover, the proposed circuit features a 2.46-μS transconductance when supplied with 0.25-V, dissipates 55-nW during operation making it suitable to low-power applications.

100-MHz monolithic low-pass filters with transmission zeros using NIC integrators

A monolithic method of implementing VHF filters with transmission zeros is presented. The transmission zeros are obtained using a modified leapfrog simulation method realized without floating capacitors that does not require summing circuits inside the feedback loops. The integrators used are balanced negative impedance converter (NIC) integrators with grounded capacitors, which do not require p-n-p transistors and are suited for low-voltage applications. A low-pass filter with a cutoff frequency of 100 MHz and with a transmission zero at 166 MHz designed and built in an integrated circuit form showed good results, confirming the feasibility of the method. >

Piezoelectric devices

The history of the discovery of piezoelectricity and its application in practical devices is traced from the late 19th century. The origin of the piezoelectric effect is outlined in terms of the symmetry of the materials, and Tables are given in which the electroelastic properties are listed for single crystals, ferroelectric ceramics and polymers which show the phenomenon. The applications of both the direct and inverse piezoelectric effect are considered in devices operating at frequencies from DC to greater than 100 GHz. Particular attention is paid to signal processing using piezoelectric substrates for surface acoustic waves, and to the use of quartz in crystal-controlled oscillators, but the whole range of devices from low frequency transducers, through acoustic and ultrasonic devices to VHF filters is discussed.

Miniaturization of wide-band VHF filters by using spiral resonators

The miniaturization of a wide-band VHF filter composed of distributed resonators has been studied. The miniaturized filter was realized with spiral resonant lines and lumped capacitors. The filter was designed using a prototype filter circuit composed of only series-resonant lumped-constant circuits. Each resonant circuit is transformed to another resonant circuit consisting of a spiral resonant line and two capacitors. One capacitor is connected to each end of the spiral resonant line. With this technique, the line length becomes very short, e.g., one-twentieth wavelength, in comparison with the line length in conventional resonant lines of one-half or one-quarter wavelength. A filter which has a 160-185 MHz passband and a volume of 3 × 4 × 10 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> was realized with 10 spiral resonators. The filter exhibits superior characteristics with very little volume.

Measurements of Intercavity Couplings (Letters)

The concept of determining intercavity couplings from frequency measurements used in the short paper by Atia and Williams was described for the case of coupling between two cavities in [2], which was referred to and portions summarized in [3]. A variation of that technique which the author has found useful for rapidly measuring the coupling between adjacent resonators in VHF filters is as follows.