CMOS continuous-time current-mode filters for high-frequencyapplications

Design considerations for high-frequency CMOS continuous-time current-mode filters are presented. The basic building block is a differential current integrator with its gain constant set by a small-signal transconductance and a gate capacitance. A prototype fifth-order low-pass ladder filter implemented in a standard digital 2 μm n-well CMOS process achieved a -3 dB cutoff frequency (f ₀) of 42 MHz; f₀ was tunable from 24 to 42 MHZ by varying a reference bias current from 50 to 150 μA. Using a single 5 V power supply with a nominal reference current of 100 μA, the five-pole filter dissipated 25.5 mW. The active filter area was 0.056 mm²/pole. With the minimum input signal defined as the input-referred noise integrated over a 40 MHz bandwidth, and the maximum input signal defined at the 1% total intermodulation distortion (TIMD) level, the measured dynamic range was 69 dB. A third-order elliptic low-pass ladder filter was also integrated in the 2 μm n-well CMOS process to verify the implementation of finite transmission zeros     

CMOS high-frequency switched-capacitor filters fortelecommunication applications

A digitally programmable high-frequency switched-capacitor filter for use in a switched digital video (SDV/VDSL) link is described. The highest available clock frequency in the system is 51.84 MHz (f_s =2f_clock=103.68 MHz for double sampling) while the three desired low-pass corner frequencies (f_c) are 8,12, and 20 MHz. The double-sampling, bilinear, elliptic, fifth-order switched-capacitor filter meets the desired -40-dB attenuation at 1.3 f _c, and -30 dB at 1.25 f_c. For the 12-MHz corner frequency setting, given the 2V_pp differential input, the measured worst case total harmonic distortion is -60 dB, with signal-to-noise ratio of 54 dB. The analog power dissipation is 125 mW from a 5-V power supply. The test results indicate that the clock frequency can be increased to 73 MHz without any ill effects. More measurements verify that an all-digital CMOS implementation, utilizing metal-sandwich capacitors, performs as well as the special-layer analog capacitors implementation, with a small reduction in the absolute corner frequencies. The prototype IC's are fabricated in a 0.35-μm 5-V (0.48 μm drawn) CMOS process     

0.5-V 5.6-GHz CMOS Receiver Subsystem

The building blocks of a 0.5-V receiver, including a receiver front-end and a low-pass filter (LPF), are fabricated using 0.18- $mu{hbox{m}}$ CMOS technology. At 5.6 GHz, the receiver front-end achieves a voltage gain of 17.1 dB and a noise figure of 8.7 dB, while dissipating at 19.4 mW. The fifth-order low-pass Chebyshev filter achieves a corner frequency of 2.6 MHz and an input-referred noise of 28.5 nV/sqrt (Hz) at 6.8 mW. The receiver front-end is further integrated with the LPFs to form a highly integrated receiver subsystem at ultra-low voltage.      

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)     

Design techniques for tunable transresistance-C VHF bandpassfilters

In this paper, a tunable wideband linear transresistance (R_m ) amplifier is proposed and analyzed. Using the tunable R_m amplifier, a new transresistance-capacitor (R_m-C) differentiator is designed. Considering the intrinsic capacitances of the MOS transistors as filter elements, this R_m-C configuration can he regarded as a very high frequency (VHF) bandpass biquadratic filter. The proposed biquad has a simple structure and thus occupies a small chip area and consumes little power. Moreover, higher-order VHF bandpass filters can be realized by directly cascading the biquads. Experimental results have successfully proven the capability of the proposed new filter implementation method in realizing VHF bandpass filters with the center frequency higher than 100 MHz when C_d=1 pF. The deviations of the measured center frequency f _o and quality factor Q of the fabricated bandpass filter from the simulated results are less than 8%. The deviation of the center frequency can be post-tuned by adjusting the control voltages V_CN and V_CP of the tunable R_m amplifier. With 1 pF differentiating capacitor, the center frequency of the fabricated VHF R_m-C bandpass filters can be tuned in a wide range larger than 30 MHz. The measured maximum signal level is 25 mV_rms and the dynamic range is 47 dB. The chip area is 0.05 mm² and power consumption is 5.05 mW with ±2.5 V power supply     

CMOS linear programmable transconductor suitable for adjustable Gm-C filters

A novel CMOS linear programmable transconductor is presented. It is based on a telescopic cascode operational transconductance amplifier with source degeneration implemented by means of highly linear tunable active resistors. The transconductor has been designed in a 0.5 mum CMOS technology featuring a third-order intermodulation (IM3) of -54.8 dB at 10 MHz for a 1 V_pp output voltage. Its feasibility for Gm-C filter design has been experimentally validated with a 1 MHz tunable third-order Chebyshev lowpass filter suitable for Bluetooth applications.     

Improved and compact 0.7 GHz tune-all bandpass filter

A compact tune-all bandpass filter is presented. This electronically tuned filter is based on series-coupled slow-wave resonators. It allows wide simultaneous and continuous tunings of centre frequency (+/-15% around 0.7 GHz) and bandwidth (from 50 to 100 MHz) with insertion loss IL<5.4 dB and return loss RL>11 dB. This two-pole bandpass filter exhibits also a very small surface of only 7.3times10^-3 lambda₀ ² and a -20 dB stop-band that extends up to 10 GHz     

A 25–75-MHz RF MEMS Tunable Filter

This paper presents a state-of-the-art discrete RF microelectromechanical systems (MEMS) tunable filter designed for 25-75-MHz operation. This paper also presents an enhanced model of the RF MEMS switch, which is used for accurate prediction of the tunable filter response. The two-pole lumped-element filter is based on digital capacitor banks with on-chip metal-contact RF MEMS switches and lumped inductors, and results in a tuning range of 3:1 with fine frequency resolution, and a return loss better than 13 dB for the entire tuning range. The relative bandwidth of the filter is 4 plusmn 1% over the tuning range and the insertion loss is 3-5 dB, limited mostly by the inductor Q and the switch loss. The IIP₃ measurements prove that tunable filters with metal-contact series RF MEMS switches show extremely linear behavior (IIP₃ > 68 dBm).     

A low-pass notch filter for bioelectric signals

Many bioelectric signals have relatively low-frequency content, but measurement devices are susceptible to power-line interference. The Type II Chebyshev low-pass filter can simultaneously perform the required low-pass filtering and removal of the narrowband interference. This filter has transfer-function zeros which result in zero gain (- infinity dB) at specific 'null' frequencies. A procedure for the low-pass filter design makes the first null frequency a design parameter so that the notch can occur at the interference frequency.<>     

Robust highly linear high-frequency CMOS OTA with IM3 below - 70 dB at 26 MHz

An enhanced configuration for a linearized MOS operational transconductance amplifier (OTA) is proposed. The proposed fully differential OTA circuit is based on resistive source degeneration and an improved adaptive biasing technique. It is robust to process variation, which has not been fully shown in previously reported linearization techniques. Detailed harmonic distortion analysis demonstrating the robustness of the proposed OTA is introduced. The transconductance gain is tunable from 160 to 340 /spl mu/S with a third-order intermodulation (IM3) below -70 dB at 26 MHz. As an application, a 26-MHz second-order low-pass filter fabricated in TSMC 0.35-/spl mu/m CMOS technology with a power supply of 3.3 V is presented. The measured IM3 with an input voltage of 1.4 Vpp is below - 65 dB for the entire filter pass-band, and the input referred noise density is 156nV//spl radic/Hz. The cutoff frequency of the filter is tunable in the range of 13-26 MHz. Theoretical and experimental results are in good agreement.     

Ultra low voltage, high performance operational transconductance amplifier and its application in a tunable Gm-C filter

This paper presents an ultra low voltage, high performance Operational Transconductance Amplifier (OTA) and its application to implement a tunable Gm-C filter. The proposed OTA uses a 0.5 V single supply and consumes 60 μw. Employing special CMFF and CMFB circuits has improved CMRR to 138 dB in DC. Using bulk driven input stage results in higher linearity such that by applying a 500 mv_p-p sine wave input signal at 2 MHz frequency in unity gain closed loop configuration, third harmonic distortion for output voltage is −46 dB and becomes −42.4 dB in open loop state for 820 mv_p-p output voltage at 2 MHz. DC gain of the OTA is 47 dB and its unity gain bandwidth is 17.8 MHz with 20 pF capacitance load due to both deliberately optimized design and special frequency compensation technique. The OTA has been used to realize a wide tunable Gm-C low-pass filter whose cutoff frequency is tunable from 1.4 to 6 MHz. Proposed OTA and filter have been simulated in 0.18 μm TSMC CMOS technology with Hspice. Monte Carlo and temperature dependent simulation results are included to forecast the mismatch and temperature effects after fabrication process.     

可变带宽OTA—C连续时间低通滤波器设计

实现了一种全集成可变带宽中频宽带低通滤波器,讨论分析了跨导放大器-电容（OTAc）连续时间型滤波器的结构、设计和具体实现,使用外部可编程电路对所设计滤波器带宽进行控制,并利用ADS软件进行电路设计和仿真验证。仿真结果表明,该滤波器带宽的可调范围为1～26MHz,阻带抑制率大于35dB,带内波纹小于0．5dB,采用1．8V电源,TSMC 0．18μm CMOS工艺库仿真,功耗小于21mw,频响曲线接近理想状态。     

A highly linear baseband G_m-C filter for WLAN application

A low voltage,highly linear transconductance-C（G_m-C） low-pass filter for wireless local area network （WLAN） transceiver application is proposed.This transmitter（Tx） filter adopts a 9.8 MHz 3rd-order Chebyshev low pass prototype and achieves 35 dB stop-band attenuation at 30 MHz frequency.By utilizing pseudo-differential linear-region MOS transconductors,the filter IIP₃ is measured to be as high as 9.5 dBm.Fabricated in a 0.35μm standard CMOS technology,the proposed filter chip occupies a 0.41×0.17 mm² die area and consumes 3.36 mA from a 3.3-V power supply.     

High-frequency high-Q BiCMOS current-mode bandpass filter andmobile communication application

The design of a tunable high-frequency fully integrable current-mode bandpass filter is presented using a complementary high-performance BiCMOS process. The new architecture of this filter is based on impedance simulation and employs current controlled conveyors. The Q-factor and the center frequency can be electronically controlled with dc bias currents over a broad range of values, thus allowing easy tuning of this filter. An application to a mobile communication IF receiver channel centered at 85 MHz and with 1-MHz bandwidth based on the cascade of two identical second-order bandpass cells has been designed. Measurements show very interesting frequency performance (f ₀ tunable in the range 30-120 MHz and Q from 1-140) in conjunction with low power consumption (25 mW for the fourth-order filter with ±2.5 V supplies)     

10 GHz dual-conversion low-IF downconverter with microwave and analogue quadrature generators

A 10 GHz dual-conversion low-IF downconverter using 0.18-mum CMOS technology is demonstrated. The high-frequency quadrature RF and LO₁ signals are generated by broadside-coupled quadrature couplers while a two-section polyphase filter is utilised for the low-frequency LO₂ quadrature signal generation. As a result, the demonstrated downconverter achieves a conversion gain of 7 dB, IP_{1 dB} of -16 dBm, IIP₃ of -5 dBm and noise figure of 26 dB at a 1.8 V supply. The image-rejection ratio of the first/second image signal is 33/42 dB for IF frequency ranging from 10 to 60 MHz, respectively.     

A BiCMOS low-distortion 8-MHz low-pass filter

An 8-MHz seventh-degree elliptic-function low-pass filter is described, demonstrating an approach to low-distortion antialias filtering for high-definition video applications. The filter's performance goals are achieved through the use of circuit design principles that capitalize on the strengths of BiCMOS technology. The integrator circuits composing the filter consist of a new wideband low-distortion transconductor circuit and a unique BiCMOS Miller-stage circuit. Integrator time constants are determined by stable RC products, enabling a simplified filter calibration scheme that is insensitive to temperature-induced variations and requires no phaselock circuits. The prototype filter IC, consisting of seven integrators assembled in an active-ladder configuration, was fabricated in a 10-V, 2-μm 2.5-GHz BiCMOS technology that also features thin-film resistors and polysilicon-plate capacitors. Measured results from the calibrated filter show passband flatness of 0.2 dB, with aberrations of less than ±1 dB over a 100°C temperature range. Stopband attenuation meets its designed goal of 60 dB. Driven by 7-V_pp, differential input signals, the filter exhibits less than -72-dBc third-order intermodulation distortion products at 1 MHz. For 5-V_pp inputs at 4 MHz, third-order intermodulation spurs remain below -65 dBc     

A low power 8th order elliptic low-pass filter for a CMMB tuner

This paper presents an 8th order active-RC elliptic low-pass filter（LPF） for a direct conversion China Mobile Multimedia Broadcasting（CMMB） tuner with a 1 or 4 MHz -3 dB cutoff frequency(f_-3dB).By using a novel gain-bandwidth-product（GBW） extension technique in designing the operational amplifiers（op-amps）, the proposed filter achieves 71 dB stop-band rejection at 1.7f_-3dB to meet the stringent CMMB adjacent channel rejection（ACR） specifications while dissipates only 2.8 mA/channel from a 3 V supply,its bias current can be further lowered to 2 mA/channel with only 0.5 dB peaking measured at the filter’s pass-band edge.Elaborated common-mode（CM） control circuits are applied to the filter op-amp to increase its common-mode rejection ratio （CMRR） and effectively reject the large signal common-mode interference.Measurement results show that the filter has 128 dBμV_rms in-band IIP3 and more than 80 dB passband CMRR.Fabricated in a 0.35-μm SiGe BiCMOS process,the proposed filter occupies a 1.19 mm² die area.     

The design of CMOS continuous-time VHF current and voltage-modelowpass filters with Q-enhancement circuits

In this paper, very high frequency (VHF) current and voltage biquadratic lowpass filters implemented directly by the linear wideband finite-gain current and voltage amplifiers, respectively, are proposed and analyzed. A new Q-enhancement circuit which consists of a finite-gain wideband tunable voltage amplifier and a Miller capacitor is also proposed. It can increase the maximum-gain frequency f_M, and enhance the maximum-gain quality factor Q_M of the VHF lowpass filters. Experimental results have successfully verified the capability of the proposed new filter implementation method in realizing both VHF current and voltage lowpass filters with maximum-gain frequency f_M tunable in the range of 148 MHz to 92 MHz. It is also shown from experimental results that the VHF current lowpass biquad with the Q-enhancement circuit has the maximum-gain frequency f_M near 185 MHz and the maximum-gain quality factor Q_M up to 18.5. A fourth-order Chebyshev current lowpass filter with the cut-off frequency of 190 MHz has been successfully designed by using the current biquads with Q-enhancement circuits     

A low-loss bandpass filter using electrically coupled high-Q TM01δ dielectric rod resonators

For a TM_01δ mode dielectric rod resonator placed coaxially in a TM₀₁ cutoff circular waveguide, characteristics such as the resonant frequency, its temperature coefficient, the unloaded Q, and the other resonances are discussed on the bases of accurate calculations using the mode-matching method. The results show that this resonator compares favorably with a conventional TE_01δ mode dielectric resonator, particularly for realization of a high unloaded Q. Analytical results also verify that interresonator coupling between these two resonators can be expressed equivalently by a capacitively coupled LC resonant circuit. A four-stage Chebyshev filter having a ripple of 0.035 dB and an equiripple bandwidth of 27 MHz at a center frequency of 11.958 GHz was fabricated using these resonators. Its insertion loss is 0.5 dB, which corresponds to an unloaded Q of 17000, and no spurious response appears in the frequency range below 17 GHz     

A 250 MHz 14 dB-NF 73 dB-Gain 82 dB-DR Analog Baseband Chain With Digital-Assisted DC-Offset Calibration for Ultra-Wideband

A 250 MHz analog baseband chain for Ultra-Wideband was implemented in a 1.2 V 0.13 $mu$ m CMOS process. The chip has an active area of 0.8 mm $^{2}$. In the analog baseband, PGAs and filters are carried out by current-mode amplifiers to achieve wide bandwidth and wide dynamic range of gain, as well as low noise and high linearity. Besides, a current-mode Sallen–Key low-pass filter is adopted for effective rejection of out-of-band interferers. A 6th-order Chebyshev low-pass filter realized in ${rm G}_{rm m}$ -C topology is designed in the baseband chain for channel selection. Digitally-assisted DC-offset calibration improves second-order distortion of the entire chain. The design achieves a maximum gain of 73 dB and a dynamic range of 82 dB. Measured noise figure is 14 dB, an IIP3 of ${-}$6 dBV, and IIP2 of ${-}$5 dBV at the maximum gain mode. The analog baseband chain consumes 56.4 mA under supply of 1.2 V.