Abstract
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. 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. 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. 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. 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. 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 mm2 and mostly a low design complexity.
Highlights
The most remarkable development in filter theory dates from the early decades of the last century [1,2,3]
Some drawbacks related to the use of Complementary Metal-Oxide-Semiconductor (CMOS) gm-C filters poke out: their parasitic capacitances are often considerable and require to be taken into account in advance in the design procedure [13]; at high frequencies, the value of the transconductance varies with frequency [15]; their useful signal dynamic range is rather low due to the nonlinearity inherent to the MOS transistors [14]
The proposals [28,29,30] report simulation results based on CMOS circuits, whereas approach [31] accounts for experimental results based on lumped resonators
Summary
The most remarkable development in filter theory dates from the early decades of the last century [1,2,3]. Some drawbacks related to the use of CMOS gm-C filters poke out: their parasitic capacitances are often considerable and require to be taken into account in advance in the design procedure [13]; at high frequencies, the value of the transconductance varies with frequency [15]; their useful signal dynamic range is rather low due to the nonlinearity inherent to the MOS transistors [14] Despite those disadvantages, huge efforts have been made in order to achieve gm-C structures with a salient functionality at very high frequencies [16,17], and with improved linearity [18,19].
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