Continuous-time Low-pass Filter Research Articles

A CMOS imager with on-chip temporal filtering for motion pre-processing

Robust motion detection algorithms such as the motion energy model require temporal filtering at the pixel level. We have designed and tested a CMOS imager with integrated, pixel-level temporal filtering necessary for motion detection. This temporal filtering enhances transients and provides a delayed and non-delayed channel for each pixel in the array. By varying bias currents on the chip, we are able to control the time constant of continuous-time low-pass filters that set the delay. By varying a reset switching frequency, we can control the high-pass filter time constant which determines the time course of transient enhancement. Operation primarily in weak inversion results in a low-power sensor well suited for integration into a motion processing system. We have constructed a 16/spl times/16 temporal processing array in a 0.5 /spl mu/m CMOS process.

Efficient arbitrary sampling rate conversion with recursive calculation of coefficients

In this paper, we present a novel algorithm for sampling rate conversion by an arbitrary factor. Theoretically, sampling rate conversion of a discrete-time (DT) sequence can be performed by converting the sequence to a series of continuous-time (CT) impulses. This series of impulses is filtered with a CT lowpass filter, and the output is then sampled at the desired rate. If the CT filter is chosen to have a rational transfer function, then this system can be simulated using a DT algorithm for which both computation and memory requirements are low. The DT implementation is comprised of a parallel structure, where each branch consists of a time-varying filter with one or two taps, followed by a fixed recursive filter operating at the output sampling rate. The coefficients of the time-varying filters are calculated recursively. This eliminates the need to store a large table of coefficients, as is commonly done.

Continuous-Time 4th Order Butterworth Low-Pass Filter for Video Frequency Applications

In this paper, a continuous-time 4th order Butterworth low-pass filter based on current-mode processing is presented for applications over the video frequency range. A new type of integrator in which both voltage and currents may be integrated is presented and used as the main active block. The filter has been implemented using a very low-cost 2.4 μm CMOS process (Mietec). The whole circuit occupies 2.8 mm2 and consumes 19 mW from a ±1.5 V supply. Experimental results are given for a 4.5 MHz to 12 MHz tunable low-pass filter with 58 dB of dynamic range at 10 MHz.

Low-power fully differential CMOS filter for video frequencies

The authors describe a new low-power fully differential second-order continuous-time low-pass filter for use at video frequencies. The filter uses a single active device in combination with MOSFET resistors and grounded capacitors to achieve very low-power consumption and large dynamic range. The ideal integrator is realized using an internally compensated op-amp consisting of only current mirrors and voltage buffers, while the lossy integrator is implemented by a single passive RC circuit. The filter has been simulated using a CMOS process. Results show that with a single 5-V power supply, cutoff frequency can be tuned from 3.5 to 8 MHz, dynamic range is better than 67 dB and power consumption is less than 1.7 mW.

A 3-V continuous-time filter with on-chip tuning for IS-95

This paper describes a low-voltage channel selection analog front end with continuous-time low-pass filters and on-chip tuning for a receiver in an IS-95 cellular phone. The filters were realized as balanced seventh-order elliptical g/sub m/C filters to achieve low current consumption. The transconductors were realized by using second-generation current conveyors (CCII) and resistors to achieve good intermodulation distortion performance. A novel CCII circuit topology was developed to fulfil the low supply-voltage requirement. The cutoff frequency tuning was implemented with capacitance matrices and a time-domain master-slave tuning circuit.

Current-Mode Temperature Compensated Continuous-Time CMOSTransconductance-C Filter

In this paper a low voltage low power current-mode continuous-time low-pass filter is presented. The current-integrator is constructed of a multi-output linearized transconductance element driven by a balanced transimpedance amplifier. A 1 MHz third order elliptic low pass filter is designed and fabricated with the proposed current-mode integrator. The measurements show capability of operation with down to a 3 V supply voltage. The measured current consumption is 850 µA at room temperature and the dynamic range is 66 dB. The distortion of the filter is below 50 dBc with peak signal levels up to twice the quiescent current level and with the refined designs even lower distortion is expected. The filter uses a CMOS-current reference for temperature and process variation stabilization with a measured corner frequency temperature coefficient of −100 ppm/K.

An integrable single-pole lowpass filter for low-frequency operation

A continuous-time lowpass filter circuit capable of achieving very low corner frequencies using integrated circuit components is reported. Corner frequencies as low as a few hertz can be economically achieved on an integrated circuit chip without using external components.

A 3 V 12-55 MHz BiCMOS pseudo-differential continuous-time filter

The reduction of the supply voltage forces one to develop system and circuit solutions able to achieve the same performance previously obtained with higher supply voltage. In this paper, a second-order low-pass continuous-time filter operating at a 3 V power supply is presented. The prototype filter is implemented using a highly linear pseudo-differential transconductor. The input common-mode signal is canceled at the transconductor level using a feed-forward path. The output common mode voltage is controlled at the filter level using lossy integrators. A prototype cell has been realized in 1.2 /spl mu/m BiCMOS technology. The pole frequency can be tuned in the range 12-55 MHz. A THD of -40 dB is achieved for signals up to 1 V/sub pp/ at 10 MHz. The dynamic range is approximately 60 dB.

A 2- mu m CMOS fifth-order low-pass continuous-time filter for video-frequency applications

A fifth-order elliptic low-pass continuous-time filter based on triode transconductors for applications in the video frequency range is presented. Fabricated in a standard 2- mu m CMOS technology, the circuit occupies 6 mm/sup 2/ of silicon area including the automatic tuning circuitry. The filter achieves a 7-MHz cutoff frequency using a parasitic pole compensation scheme. The dynamic range is 40 dB and power consumption is 30 mW for a 5-V supply. A transconductor biasing strategy which allows a continuous tuning range for the cutoff frequency of one decade is presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A micropower CMOS continuous-time low-pass filter

A continuous-time third-order Butterworth low-pass filter with a nominal cutoff frequency of 945 Hz implemented in a standard 2.4- mu m CMOS process is discussed. The filter is built from fully balanced linearized transconductors and capacitors. The power consumption of the filter, including bias and automatic-tuning circuits, is 12.6 mu W from a single 3-V power supply. It achieves a dynamic range of 63 dB with a total harmonic distortion of less than 0.5%. The total chip area is 1 mm/sup 2/.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 4-MHz CMOS continuous-time filter with on-chip automatic tuning

A third-order elliptic low-pass continuous-time filter with a 4-MHz cutoff frequency, integrated in a 3- mu m p-well CMOS process, is presented. The design procedure is based on the direct simulation of a doubly terminated LC ladder filter by capacitors and fully balanced, current-controlled transconductance amplifiers with extended linear range. The on-chip automatic tuning circuit uses a phase-locked loop implemented with an 8.5-MHz controlled oscillator that matches a specific two-integrator loop of the filter. The complete circuit features 70-dB dynamic range (THD<-50 dB) and consumes only 16 mW from +or-2.5-V supplies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Timing-controlled fully programmable analogue signal processors using switched continuous-time filters

Analog signal processors based on continuous-time emulation of sampled-data networks are presented. In these processors, continuous-time signal delay is realized using the phase shift of fixed-frequency, fixed-Q, continuous-time low-pass filters (LPFs), and analog multiplication is accomplished through signal switching using digitally programmable duty cycles. Each coefficient of the processor transfer function is dependently programmable, without requiring selectable capacitor (or resistor) arrays. Experiments verify that this method can be used to construct analog processors with arbitrarily programmable frequency responses. The results presented here are complementary to other results presented earlier by the authors, using sample-data delays.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

High-frequency voltage-controlled continuous-time lowpass filter using linearised CMOS integrators

The design and implementation of a continuous-time lowpass filter with voltage-controlled cutoff frequency and passband ripple is presented. The circuit uses a linearised CMOS transconductor as a basic integrating building block. A voltage-controlled phase-adjusting scheme is employed in the integrator to compensate for excess phase in the transconductance at high frequencies. The fabricated filter is capable of realising cutoff frequencies as high as 2 MHz and handles single-ended input signals up to 4 V p-p with less than 1% distortion.

Fully integrated active RC filters in MOS technology

A fully integrated continuous-time low-pass filter has been fabricated with CMOS technology. The device implements an active RC network using integrated capacitors and MOS transistors operated in the nonsaturation region as voltage-controlled resistors. The filter topology is fully balanced for good linearity and for good power supply rejection. The cutoff frequency is voltage adjustable around 3 kHz, allowing compensation for process and temperature variations. For 5-V power supplies a dynamic range of over 94 dB has been achieved.