A multipurpose micropower SC filter

A design strategy for micropower switched-capacitor filters is presented and illustrated with the design of a multipurpose second-order section. The filter, realized in a double-poly 6-/spl mu/m CMOS process, consumes 237 /spl mu/W if it is used as an equalizer (f/SUB c/=90 kHz, -V/SUB DD/=3 V) and only 72 /spl mu/W if it is used as a bandpass filter for 8 channels (f/SUB c/=192 kHz, V/SUB DD/=3 V). The dynamic range of the filter is over 60 dB and the total chip area is 3.5 mm/SUP 2/, including bonding pads.     

A micropower fourth-order elliptical switched-capacitor low-pass filter

A micropower fourth-order elliptical switched-capacitor (SC) low-pass filter for biomedical applications has been designed and measured. The charge transfer error of an SC integrator using a transconductance amplifier is discussed. Also first-order noise and PSRR calculations are performed and compared with the results of simulations and measurements. The measurements show that by careful optimization of the gain bandwidth, slew rate, and gain of the amplifiers, high-performance low-power SC filters can be constructed. The cutoff frequency of the filter is 5 kHz, the ripple in the passband is 0.27 dB, and stopband rejection is 49 dB. The power consumption of the filter is 190 /spl mu/W with /spl plusmn/2.5-V power supplies. The dynamic range of the filter is 75 dB, and the total harmonic distortion over the whole passband range is below 0.25% for a 2-V/SUB pp/ input signal. The PSRR of the filter is above 40 dB at frequencies below 3 kHz.     

Large-value monolithic resistors for micropower integrated circuits

The minimum power dissipation of micropower integrated circuits is often limited by the availability of large-value monolithic resistors. Two major types of field-effect resistor structures are examined and an analysis of the primary factors that determine sheet resistance and parasitic capacitance is presented. Resistor tolerance, linearity, and temperature coefficient are briefly discussed. It is shown that resistors with sheet resistances greater than 50 k/spl Omega///spl square/ and parasitic capacitances less than 0.002 pF/k/spl Omega/ can be readily fabricated in a monolithic structure.     

CMOS VHF transconductance-C lowpass filter

Experimental results of a VHF CMOS transconductance-C lowpass filter are described. The filter is built with transconductors as published earlier. The cutoff frequency can be tuned from 22 to 98 MHz and the measured filter response is very close to the ideal response.<>     

A micropower class-AB CMOS log-domain filter for DECT applications

This paper presents a micropower second-order low-pass filter using the log-domain principle and integrated in a 0.35-μm CMOS process. It has been designed as an antialiasing filter for a DECT transceiver with a 45-kHz nominal cutoff frequency. The circuit uses transistors biased in weak inversion without requiring separate wells. It operates at 1.5-V supply voltage and its current consumption is 8 μA in idle mode. The log-domain filter is implemented with an on-chip conditioner which allows class-AB operation. It can process input currents at 5 kHz that are 25 times larger than the 200-nA bias current. Measurements up to 500 times the bias current have been done, since at 1 kHz the input current is only limited by the supply voltage     

A micropower CMOS continuous-time filter with on-chip automatic tuning

This paper presents a CMOS implementation of a low-voltage micropower G/sub m/-C biquad with on-chip automatic tuning. The filter is suitable for any kind of application involving low-frequency ranges, and very low-power consumption, such as biomedical devices. The operational transconductance amplifier (OTA) is implemented with the transistors working in the weak inversion saturation region, thus allowing the use of very small currents that minimize the power consumption. The aspect ratios are small enough not to degrade the frequency response. The tuning algorithm is based on amplitude tracking. The filter output amplitude is quantized using a low-power amplifier and an asymmetric comparator. A digital controller varies the tuning parameters until the maximum quantized amplitude is found. The system works down to a voltage supply of 1.75 V. The center frequency is tunable over one and a half decades, from 300 Hz to 10 kHz for bias currents changing from 6 to 200 nA and a 20-pF integrating capacitance, giving an overall filter accuracy of up to 99.55%. The power consumption of the second-order filter including the common-mode correction circuitry is in the order of 200 nW for the 10-nA bias current. It exhibits a dynamic range of 54 dB and occupies an area of 0.06 mm/sup 2/ excluding the area of the integrating capacitances.     

Distributed control of renewable generation units with integrated active filter

Due to the current concern about the environment, there is a growing interest in distributed generation from renewable energy sources. Usually a power electronic converter is required to interface renewable generation units with the utility grid. The power electronic converters can be designed to provide nonactive power in addition to active power supply in order to compensate distorted currents. This paper proposes a distributed control method for converter-interfaced renewable generation units with active filtering capability. Agent-based communication makes coordination between the generation units possible. Experimental results are included to demonstrate the validity of the proposed method.     

Design of a hybrid integrated circuit elliptic active RC filter

Discusses design details and experimental results obtained in realizing hybrid IC sharp rolloff filters. Practical low and high pass audio active RC filters were produced in large quantities with rolloff characteristics of approximately 500 dB/octave.     

A transistor-only low-pass filter with adjustable bias and smallphase shift at high frequencies

A third-order, low-pass, transistor-only filter with a small phase shift at high frequency and an adjustable cutoff frequency is presented. This low-pass filter overcomes the structure limit of the filter previously reported and achieves the same frequency response. It has an adjustable bias voltage which makes it possible to change its cutoff frequency     

A practical micropower programmable bandpass filter for use in bionic ears

Subthreshold Gm-C filters offer the low power and wide tunable range required for use in fully implantable bionic ears. The major design challenge that must be met is increasing the linear range. A capacitive-attenuation technique is presented and refined to allow the construction of wide-linear-range bandpass filters with greater than 1 V/sub pp/ swings. For a 100-200 Hz fully differential filter with second-order roll off slopes and greater than 60 dB dynamic range, experimental results from a 1.5-/spl mu/m, 2.8-V BiCMOS chip yield only 0.23 /spl mu/W power consumption; for a 5-10 kHz filter with the same specifications the power only increased to 6.36 /spl mu/W. Fully differential filters with first-order slopes had a dynamic range of 66 dB and power consumptions of 0.12 and 3.36 /spl mu/W in the 100-200 Hz and 5-10 kHz cases, respectively. We show that our experimental results of noise and linear range are in good accord with theoretical estimates of these quantities.     

CMOS filter with wide digitally programmable VHF range

A novel approach is presented for programmable filtering over the VHF range based on fully-balanced pseudo-differential continuous-time transconductors for applications in low-voltage systems. An example third-order G_m-C lowpass Butterworth filter using the proposed transconductor and accumulation MOS capacitors has been implemented using an AMS 0.35 mum CMOS process, achieving -3 dB cutoff frequencies ranging from 40 to 200 MHz. The active chip area is 0.06 mm ² per pole     

Stability analysis of a series active filter integrated with adouble-series diode rectifier

This paper deals with a harmonic current-free AC/DC power conversion system which is characterized by the integration of a small-rated series active filter with a large-rated double-series diode rectifier. The stability of the active filter based on feedback control is discussed theoretically, taking into account delay time in the control circuit. As a result, it is revealed that the delay time may produce a bad effect on stability, especially when the power conversion system is installed on a stiff power system with low system inductance. The authors propose a viable way of reducing the effect of delay time on the system stability. Analysis in the frequency domain enables us to know how much the system stability is improved in terms of gain and phase margins. A switching-ripple filter is designed to obtain good filtering performance without affecting the system stability. Experimental results obtained from a 20 kW laboratory system verify the validity of the developed theory, and confirm the viability and effectiveness of the proposed control circuit     

Analog integrated filter compilation

A review of the progress in automated design of analog integrated filters is presented. Such tools are ahead of other analog circuit automation in terms of the acceptance by designers and practical applicability. A survey of the present-day commercial and academic systems is made and the range of facilities available is compared. The problems faced in the design of this type of software are typical of the problems of analog design systems in general; lack of openness for introduction of new design knowledge, difficulties of dealing simultaneously with expert and novice users, poor integration in design environments, and user-interface problems. The structure of a typical system is studied and the computer methods used within are discussed with regard to such issues as speed, flexibility, and ease-of-use. Some future directions for analog filter compilers are proposed.     

A 1.25-V micropower Gm-C filter based on FGMOS transistors operating in weak inversion

This paper presents a novel linearized transconductor architecture working at 1.25 V in a 0.8-/spl mu/m CMOS technology with very low power consumption. The special features of the floating-gate MOS (FGMOS) transistor are combined in weak and strong inversion leading to a simplified topology with fewer stacked transistors and a very low noise floor. The design methodology is thoroughly explained, together with the advantages and disadvantages of working with the FGMOS transistor. Furthermore, second-order effects arising from nonideal behavior of the device are analyzed and limits for the performance are established. Experimental results from a second-order low-pass/bandpass filter that was implemented using the transconductor show a tunability of over one and a half decades in the audio range, a dynamic range of over 62 dB, and a maximum power consumption of 2.5 /spl mu/W. These results demonstrate the suitability of the FGMOS transistor for implementing analog continuous-time filters, while at the same time pushing down the voltage limits of process technologies and simplifying the circuit topologies to obtain significant power savings.     

CMOS VHF/RF CCO based on active inductors

A novel CMOS current controlled oscillator (CCO) is proposed. Based on the current-reused active inductors, a differential oscillator has been designed and fabricated. Measurement results show that it has very wide tuning-range and reasonable phase-noise performance     

Fully integrated MIXLER based on VHF CMOS-MEMS clamped-clamped beam resonator

The design and test of a fully integrated CMOS-MEMS-MIXLER, using a commercial technology (AMS 0.35 mum) is presented. The MEMS structure is basically a clamped-clamped beam resonator implemented with the polysilicon capacitance module of the selected technology, showing a fundamental lateral resonance frequency of 22.5 MHz. Two different approaches based, respectively, on the nonlinearity of the voltage against the excitation force and on the amplitude modulation of the excitation signal, have been proposed in order to operate the MEMS as a MIXLER     

A 4th order fully integrated active RC complex filter with novel automatic tuning systems

This letter introduces a 4th order active RC complex filter with 1.5MHz center frequency and 1MHz bandwidth. The total harmonic distortion of the filter is less than –60dB and the image rejection ratio is greater than 60dB. A novel technique is also proposed in this letter to automatically adjust the variation of the time constant. The advantages of the proposed method are its high precision and simplicity. Using 5bits control words, the tuning error is less than ±1.6%.     

A vertically integrated micromachined filter

A 10-GHz filter constructed of slot-coupled micromachined cavities in silicon is presented. The novel character of the filter lies in its structure, which consists of a microstrip feed to cavities via slot apertures and three vertically stacked slot-coupled cavities. The cavities are essentially reduced-height waveguide resonators. The measured results are presented and compared to a finite-element-method model. The simulated model has a bandwidth of 4% with an insertion loss of 0.9 dB at 10.02 GHz. The measured filter yields a 3.7% bandwidth with a deembedded insertion loss of 2.0 dB at 10.01 GHz. Various loss mechanisms are examined to explain the difference between simulated and measured insertion loss     

VHF radio link for ground-air-ground communications using an integrated voice-data modulation

A possible realisation of a data channel between aircraft and ground station is presented, which utilises a combined amplitude-phase modulation. Amplitude modulation is used to transmit a voice signal, while phase modulation is used for data transmission. Performance of this system is evaluated through a computer simulation.