Filters In CMOS Technology Research Articles

Design automation of a lossless multiport network and its application to image filtering

The paper presents expert tools which are elaborated on the basis of synthesis method of lossless nonreciprocal multiport circuits, composed of gyrators and capacitors. The algorithms are written in C++ and the tools compose a user friendly environment for design automation of filters, filter pairs and filter banks. It is possible to design in this environment not only classical structures like Butterworth, Chebyshev, and Cauer (elliptic) filters. The lossless nonreciprocal prototype circuit allows to design more complex filters, including allpass sections necessary to improve filter phase characteristics. However, the most important possibility is to design multiport circuits, especially in the case of not fully determined filter specifications. On each stage of the design process VHDL-AMS is used to describe the circuits. The obtained prototype gyrator-capacitor circuit can be implemented in OTA-C, SC (switched-capacitor) or SI (switched-current) techniques to realize the filter in CMOS technology. In the paper SI technique is used for layout generation of an image filter in order to illustrate the elaborated synthesis algorithms and tools.

Widely Programmable High-Frequency Active RC Filters in CMOS Technology

We propose a circuit technique that enables the realization of widely programmable high-frequency active RC filters in CMOS technology. A fifth-order Chebyshev ladder filter having a digitally programmable 3-dB bandwidth (from 44 to 300 MHz) is used as a vehicle to validate our ideas. The opamp uses feedforward compensation for achieving high dc gain and wide bandwidth. The integrating resistors are realized as a series combination of a triode-operated MOSFET and a fixed polysilicon resistor. A charge-pump-based servo loop servoes the integrating resistor to a stable off-chip resistor. The principle of ldquoconstant capacitance scalingrdquo is applied to the opamp and the integrating resistors so that the shape of the frequency response is maintained when the bandwidth is scaled over a 7 times range. The filter core, designed in a 0.18-mum CMOS process, consumes 54 mW from 1.8-V supply and has a dynamic range of 56.6 dB.

Design of 60- and 77-GHz Narrow-Bandpass Filters in CMOS Technology

This paper investigates the design and implementation of millimeter-wave narrow-bandpass filters in a standard 0.18- m CMOS technology. Filters with a measured 10% 3-dB bandwidth at 60 and 77 GHz are realized in a thin-film microstrip structure by using the lowest metallization layer as a ground plane. The impact of dissipation losses of the filters is also examined. It is found that the metallization losses in the coupled-line filter as well as the ground plane are the main reasons for the insertion loss.

A Methodology for Long Time Constant Log-Domain Filters in CMOS

A simple methodology for implementation of low-order, current-mode, log-domain filters in CMOS technology is presented. The key transistors in the circuit are operated in weak inversion and in contrast with previous approaches may pass into the triode regime. The concept is particularly suited to implementation in silicon-on-insulator technology, because dielectric isolation of the transistors eliminates leakage currents, and because influence of the body effect on circuit function is limited. Very long time constants, on the order of 1 s or more, are obtainable. A simple elaboration of the basic unit circuit allows the time constant to be controlled by a bias current.

A systematic approach for realizing biquadratic current-mode filters using CMOS technology

A systematic method for realization of biquadratic current-mode filters in CMOS technology is proposed. The basic building blocks are lossy and ideal integrators realized from CMOS transconductors and current mirrors/amplifiers. Theoretical analysis leading to the general biquadratic transfer functions is provided and the design equations for popular filter functions are tabulated. Characteristics of the basic building blocks are discussed followed by several examples to illustrate the design technique. Simulation results are provided to verify the designs.

Versatile architecture for current-mode biquadratic filters in CMOS technology

A versatile programmable current-mode architecture for realising a given second order biquadratic filter is proposed. The architecture consists of programmed interconnections of three basic building blocks: transconductance cells, buffered current mirrors and current buffer cells. In the case of stand-alone IC chips, transfer function coefficients are set through external control voltages, and in the case of an analogue/digital mixed mode VLSI environment, through internal control voltages. Designs for a video-band lowpass notch filter and a high-frequency bandpass filter realisable using 1.2 micron CMOS technology and consuming, respectively, 1.96 mW and 2.36 mW of power, are presented as illustrations. It is expected that optimised designs will lead to reduced power consumption.

A 5th order lowpass current mode wave active filter in CMOS technology

In this paper, we present measured results from the first reported integrated current mode wave active filter. The prototype is a fifth order lowpass filter, the cutoff frequency is 3 MHz and the filter is realized in 1.2μ CMOS technology. A brief description of the synthesis method shows that it is possible to use low gain OTA amplifiers and to compensate for the phase errors of the active building blocks by tuning transconductance gain; measured results bear out these theoretical points.

Design of a low-distortion 22-kHz fifth-order Bessel filter

A linearity improvement technique employing passive resistors and current-steering MOS transistors as a variable resistance element is proposed to implement a low-distortion filter in CMOS technology. This proposed implementation relies on the linearity of the passive resistors and the tunability of the current-steering MOS transistors operating in the triode region to overcome the limited linearity performance in continuous-time electronically tunable filters. By using the existing systematic feedback loops in the active filters and placing the nonlinear elements inside the feedback, the distortion resulting from the nonlinear devices is greatly reduced by the filter loop gain. A 22-kHz fifth-order Bessel filter, its dynamic range optimized by applying Karmarkar's rescaling algorithm and self-tuned with a switched-capacitor reference resistor, demonstrates better than -90-dB THD with a 2-kHz, 4-V/sub pp/ signal in 5-V 2- mu m CMOS. >

On the design of a real-time digital median filter

This paper details the design of a high performance monolithic digital median filter in CMOS technology. The circuit selects the median value from a window of three or five data points. This implementation accepts 16-bit data which may be in either unsigned magnitude or two's complement representation. Parallelism helps deliver a new median every clock cycle at high frequencies.