![]() Furthermore, high selectivity filtering also requires pole pairs to be complex conjugate with some some of them having high quality factor ( Q). Increasing filter order adds complexity, chip area, and power consumption. However, to enhance the selectivity, which is the ability to pass a set of signals within a bandwidth while rejecting the waveforms outside the band pass, it is a common practice to increase the order (number of transfer-function poles) of the filter. ![]() ![]() Despite those disadvantages, huge efforts have been made in order to achieve gm-C structures with a salient functionality at very high frequencies, and with improved linearity. On the other hand, some drawbacks related to the use of CMOS gm-C filters also poke out: their parasitic capacitances are often considerable and require to be taken into account in advance in the design procedure at high frequencies, the value of the transconductance varies with frequency their useful signal dynamic range is rather low due to the nonlinearity inherent to the MOS transistors. There are several major advantages to using CMOS gm-C filters as compared to the Operational Amplifier (Op-Amp) RC approximations, for instance, their higher frequency ranges with simple tuning, and the fact that gm-C and digital signal processing circuits can be fabricated on the same chip, which reduces the cost and size at the same time that increases the reliability of the hardware. Such is the case of Transconductance-Capacitance ( gm-C) filters. Unfortunately, a confined number of analog filters are realized in active form because they have proved to be the most reliable and versatile in terms of circuit realization, sensitivity, and mathematical complexity. If difficult trade-offs in their implementation did not limit their usefulness, continuous time filters would be employed in many more applications. Some of the assignments that analog filters can carry on include: frequency duplexing in radar and radio communication systems impedance matching in power amplifiers upper-sideband and lower-sideband suppression in upconversion and downconversion mixers, respectively anti-aliasing in data converters, among others. While many filtering tasks use digital signal processing, continuous-time filters are still important. Digital filtering is employed in a vast cluster of applications such as voice encoding/decoding, image processing, control systems, data compression, and telecommunications, to name a few. Examples of such filter architectures are digital filters. As signal processing in electronics engineering became more relevant, this branch of knowledge evolved rendering filter structures capable of accomplishing functions whose theoretical background is rigorous and elegant at the same time. The most remarkable development in filter theory dates from the early decades of the last century. ![]() The most salient features of the proposed notch biquad include: the selectivity, whose value is comparable to that of a 7th order elliptic approach and some other 3rd order filters a high-frequency operation without resonators linearity, with a +15 dBm I I P 3 a reduced form factor with a total occupied area of 0.004282 mm 2 and mostly a low design complexity. The attained simulation results prove that the proposal is competitive compared to the FDNR solution and some other state-of-the-art filters reported in the literature. To compare the performance of the proposal with some other solution, the design of a 7th order elliptic notch filter based on Frequency Dependent Negative Resistors (FDNRs) was also accomplished. As a practical example, the design of a notch filter intended to suppress interferers in the lower sideband (400 MHz) of the Medical Implant Communication Service (MICS), in single-poly, 6-metal layers Mixed-Signal/RF 0.18 µm CMOS technology is realized. The methodology for the reconstitution of a given transfer function by means of Signal Flow Graphs (SFG) manipulation in canonical form is proposed leading to a fully differential g m- C biquad filter. A design strategy for the synthesis of high-selectivity/low-order analog filters in Complementary Metal-Oxide-Semiconductor (CMOS) technology for very high frequency (VHF) applications is presented.
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