High-linearity continuous-time filter in 5-V VLSI CMOS

High-linearity self-tuning continuous-time filters, fabricated in a standard 1.6-μm 5-V CMOS process, are presented. Frequency control is achieved using switchable arrays of highly linear double-polysilicon capacitors in an active RC filter structure, resulting in tunable filters with very low signal distortion. One filter, a Tow-Thomas biquad, exhibits dynamic range and signal linearity of typically 91 dB. Another smaller implementation, a Sallen and Key filter, attains ⩾76 dB. Cutoff frequency response is maintained to an accuracy of around ±5%     

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_mC 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     

A 2-V/sub pp/ 80-200-MHz fourth-order continuous-time linear phase filter with automatic frequency tuning

A CMOS 80-200-MHz fourth-order continuous-time 0.05/spl deg/ equiripple linear phase filter with an automatic frequency tuning system is presented. An operational transconductance amplifier based on transistors operating in triode region is used and a circuit that combines common-mode feedback, common-mode feedforward, and adaptive bias is introduced. The chip was fabricated in a 0.35-/spl mu/m process; filter experimental results have shown a total harmonic distortion less than -44 dB for a 2-V/sub pp/ differential input with a single 2.3-V power supply. The group delay ripple is less than 4% for frequencies up to 1.5 f/sub c/. The frequency tuning error is below 5%.     

A ±1.5-V, 4-MHz CMOS continuous-time filter with asingle-integrator based tuning

A 4-MHz, fifth-order elliptic low-pass Gm-C filter is described whose characteristics are tuned by an on-chip automatic tuning circuit. The tuning circuit uses only one integrator as the master of tuning instead of problematic voltage controlled oscillator (VCO) and voltage controlled filter (VCF). MOS transistors in linear operation region perform the voltage-to-current conversion in an operational transconductance amplifier, and thereby we achieved ±1.5 V operation. A prototype filter was implemented in a 0.8-μm double-poly, double-metal CMOS process. The filter exhibits the dynamic range of 57.6 dB and dissipates 10 mW with ±1.5-V supply. The stopband attenuation is better than 45.0 dB and the passband ripple is smaller than 1.0 dB     

A MOSFET-only continuous-time bandpass filter

A MOSFET-only filter is described which employs an amplifier-regulated cascode structure to realize both conductance and transconductance, while the required capacitors are realized by MOSFET gate capacitance. Distortion due to mobility degradation and MOSFET capacitor nonlinearity is analyzed, as is the effect of finite gain-bandwidth product of the regulating amplifiers on the filter's linearity and high frequency performance. A prototype second-order bandpass filter has a center frequency of 560 kHz, a third-order intermodulation of -41 dB for 0 dBm input and a dynamic range of 60 dB. It consumes 2.5 mW from a 5 V supply and occupies 0.18 mm² in a 1-μm digital CMOS technology     

A high-dynamic-range integrated continuous-time bandpass filter

An eighth-order Butterworth bandpass filter, operating at 100 kHz with a quality factor of 14.3, is presented. The filter features an optimized dynamic range, a large tuning range, and a small occupied chip area of 0.25 mm² owing to very simple circuitry. Measurements show a very accurate realization of the desired transfer function, a high dynamic range of 62 dB, and a tuning range from 50 to 200 kHz. It is shown how the dynamic range can be improved to a theoretical maximum if circuit simplicity is sacrificed     

A 60-mW 200-MHz continuous-time seventh-order linear phase filter with on-chip automatic tuning system

A full CMOS seventh-order linear phase filter based on g/sub m/-C biquads with a -3-dB frequency of 200 MHz is realized in 0.35-/spl mu/m CMOS process. The linear operational transconductance amplifier is based on complementary differential pairs in order to achieve both low-distortion figures and high-frequency operation. The common-mode feedback (CMFB) employed takes advantage of the filter architecture; incorporating the load capacitors into the CMFB loop improves further its phase margin. A very simple automatic tuning system corrects the filter deviations due to process parameter tolerances and temperature variations. The group delay ripple is less than 5% for frequencies up to 300 MHz, while the power consumption is 60 mW. The third-harmonic distortion is less than -44 dB for input signals up to 500 mV/sub pp/. The filter active area is only 900 /spl times/ 200 /spl mu/m/sup 2/. The supply voltages used are /spl plusmn/1.5 V.     

A BiCMOS continuous-time filter for video signal processingapplications

A fully integrated BiCMOS continuous-time filter for video signal processing applications is presented. It incorporates an input clamping circuit, a third-order equalizer, a fifth-order elliptic filter with sinx/x correction, and a 75-Ω driver. The architectures of the input and output amplifiers as well as the filter and the equalizer are chosen based on the extensive study of circuit structures and Monte Carlo simulation to meet the linearity requirement for the broadcast-quality video system. The complete chip achieves a low-pass filter response with a 5.5-MHz cutoff frequency (f_cc), 0.3-dB passband ripple, 20-ns group delay variation up to 0.9 f_c, and 43-dB attenuation at 1.45 f_c. With a nominal 2-Vpp signal at the output, measured results show 0.2% differential gain, 0.38° differential phase, and 1.7-mV rms noise demonstrating 10-bit linearity in a 1.5-μm 4-GHz BiCMOS process technology. The filter active area is 8 mm² and it dissipates 350 mW in a single 5-V power supply     

A bipolar integrated continuous-time filter with optimized dynamicrange

In the design of integrated continuous-time filters it is often difficult to choose a proper integrator circuit because the relative merits of the different possibilities are little known. A thorough analysis of all the possible circuits is necessary. In this work, the design and an accurate analysis of the noise and distortion properties of one type of integrator, based on a tunable bipolar transconductor, are given. The analysis is used to optimize the dynamic range, and the results are verified by simulation and measurement. A fifth-order low-pass filter design and implementation are presented to illustrate the usefulness of the designed integrator     

Piezoelectric transducer tuned bandstop filter

A tunable bandstop filter with a wide tuning range is presented. A piezoelectric transducer with an attached dielectric perturber is used to perturb the filter to obtain a wide tuning range. Without changing the dimensions of the bandstop filter the tunable bandstop can provide a wide tuning range of 25% from 4.5 to 6 GHz. The high performance bandstop filter is useful for many microwave applications     

A current-mode continuous-time filter for software defined radio solutions

A 3rd-order continuous-time current-mode filter in 65 nm CMOS technology is presented. The filter has a switchable cut-off frequency between 1.1 and 4.4 MHz and is designed for software defined radio on chip (SDR) solutions. An innovative extension to structures in literature is proposed, that allows saving chip area at low cut-off frequencies. Furthermore a mathematical estimation is presented to show the usability of the structure. The realized chip has an active area of 350 μm × 220 μm and consumes 12.3 mW at 1.2 V. The dynamic range for a bandwidth of 1.1 MHz is 77.2 dB, the in-band output current noise is \(31.16\,\hbox{pA}/\sqrt{\hbox{Hz}}\) and the IIP3 is 1.8 mA_p.     

A low-frequency,continuous-time notch filter using Gm-C circuits

A 60Hz notch filter that can be integrated on a chip is reported. G_m-C filters are used for the necessary time constant multiplication. This filter can easily be tuned and is relatively insensitive to temperature variation. The notch depth can reach 60dB.     

A Gm-C continuous-time anti-alias filter for UWB analog front-end

A proposed constant drain-source transconductor topology is designed to keep linearity at high frequency. By using the proposed operational transconductance amplifier as a building block, a fourth-order low-pass filter is realized. The filter was fabricated in 0.18 μm CMOS technology and feathers a 250 MHz cutoff frequency. The measured IM3 performance is ?36 dB at 0.6 V_pp input swing and the power consumption is 22 mW.     

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.     

Design of a bipolar 10-MHz programmable continuous-time 0.05°equiripple linear phase filter

A bipolar seventh-order 0.05° equiripple linear phase (constant group delay) transconductance-capacitor (g_m-C) low-pass filter with a cutoff frequency (f_c) tunable between 2 and 10 MHz is presented. Programmable equalization up to 9 dB at f_c is also provided. Total harmonic distortion at 2 V_p-p is less than 1%, with a dynamic range equal to 49 dB. Nominal power consumption from a single 5-V supply is 135 mW. The circuit also has a low-power mode (<0.5-mW dissipation)     

A 1-V CMOS switched-opamp switched-capacitor pseudo-2-path filter

A modified switched-opamp technique is proposed to enable switched-capacitor (SC) circuits to operate at 1 V with the opamp fully functional in all phases. A 1-V fully differential two-switchable-output-pair operational amplifier has been designed for the proposed technique, which is then employed in a 1-V fully differential SC pseudo-2-path filter. Implemented in a standard single-poly triple-metal 0.5-μm CMOS process, the filter achieves a sixth-order bandpass response centered at 75 kHz with a quality factor of 45. Capacitors formed with polysilicon and highly doped n-well (cap-well option) regions are used to achieve both good linearity and small chip area. At 1-V supply, the filter obtains an output swing of 1.2 V_pp and a dynamic range of 51 db while dissipating 310 μW and occupying a chip area of 0.8 mm²     

Electronically tuned filter using p-i-n diodes

An electronically tuned microwave filter employing p-i-n diodes is described. Experimental results for a 2-section device tuning from 0.8 to 1.2 GHz are given.     

X-band RF MEMS tuned combline filter

A three-pole combline filter tuning from 8.2 to 11.3 GHz using RF MEMS switched capacitors is reported. This structure, measuring 2.85/spl times/2.15 mm/sup 2/, allows 31% tuning with 11% 3 dB bandwidth for the four tuning states and insertion losses ranging from 4.4 to 6 dB.