A rail-to-rail input/output CMOS power amplifier

A rail-to-rail amplifier that maintains a high common-mode rejection ratio (CMRR) over the whole common-mode range and has a low harmonic distortion despite the use of relatively small output devices is discussed. The circuit, which measures only 0.3 mm² in a 3-μm technology, has a quiescent current consumption of 600 μA and a CMRR larger than 55 dB. It handles up to 4 nF, and can, with a 5-V supply, drive 3.8 V_pp into 100 Ω (0.1% total harmonic distortion at 10 kHz)     

A compact low noise operational amplifier for a 1.2 μm digitalCMOS technology

A compact low noise operational amplifier using lateral p-n-p bipolar transistors in the input stage has been fabricated in a standard 1.2 μm digital n-well CMOS process. Like their n-p-n counterparts in p-well processes, these lateral p-n-p transistors exhibit low 1/f noise and good lateral β. The fabricated op amp has an area of only 0.211 mm² with E_n=3.2 nV/√(Hz), I_n=0.73 pA/√(Hz), E_n and I_n 1/f noise corner frequencies less than 100 Hz, a -3 dB bandwidth greater than 10 MHz with a closed loop gain of 20.8 dB, a minimum PSRR (DC) of 68 dB, a CMRR (DC) of 100 dB, a minimum output slew rate of 39 V/μs, and a quiescent current of 2.1 mA at supply voltages of ±2.5 V. The operational amplifier drives a 1 kΩ resistive load to 1 V peak-to-peak at 10 MHz and has been used as a versatile building block for mixed-signal IC designs     

A Novel Resistor-Free Electronically Adjustable Current-Mode Instrumentation Amplifier

In this paper, a novel topology for implementing resistor-free current-mode instrumentation amplifier (CMIA) is presented. Unlike the other previously reported instrumentation amplifiers (IAs), in which input and/or output signals are in voltage domain, the input and output signals in the proposed structure are current signals and signal processing is also completely done in current domain benefiting from the full advantages of current-mode signal processing. Interestingly the CMRR of the proposed topology is wholly determined by only five transistors. Compared to the most of the previously reported IAs in which at least two active elements are used to attain high common-mode rejection ratio (CMRR) resulting in a complicated circuit, the proposed structure enjoys from an extremely simple circuit. It also exhibits low input impedance employing negative feedback principal. Of more interest is that, using simple degenerate current mirrors, the differential-mode gain of the proposed CMIA can be electronically varied by control voltage. This property makes it completely free of resistors. The very low number of transistors used in the structure of the proposed CMIA grants it such desirable properties as low-voltage low-power operation, suitability for integration, wide bandwidth etc. SPICE simulation results using the TSMC 0.18-μm CMOS process model under supply voltage of ±0.8 V show a high CMRR of 91 dB and a low input impedance of 291.5 Ω for the proposed CMIA. Temperature simulation results are also provided, which prove low temperature sensitivity of the proposed CMIA.     

A high-swing CMOS telescopic operational amplifier

A high-swing, high-performance CMOS telescopic operational amplifier is described. The high swing of the op-amp is achieved by employing the tail and current source transistors in the deep linear region. The resulting degradation in differential gain, common-mode rejection ratio (CMRR), and other amplifier characteristics are compensated by applying regulated-cascode differential gain enhancement and a replica-tail feedback technique. A prototype of the op-amp has been built in a 0.81-μm CMOS process. Operating from a power supply of 3.3 V, it achieves a differential swing of ±2.15 V, a differential gain of 90 dB, unity-gain frequency of 90 MHz, and >50-dB CMRR. It is shown, analytically and through simulations, that the operational amplifier maintains its high CMRR even at high frequencies     

Constant-gm rail-to-rail CMOS op-amp input stage withoverlapped transition regions

Conventional techniques to achieve a constant-g_m rail-to-rail complementary N-P differential input stage require complex additional circuitry. In addition, the frequency response and common-mode rejection ratio (CMRR) are degraded. An economical but efficient design technique to overcome these problems is proposed. The proposed technique strategically overlaps the transition regions of the tail currents for the n- and p-pairs to achieve constant overall transconductance. Experimental results demonstrate that g_m variation can be restricted to within ±4% with improved CMRR and frequency response     

A high CMRR, class AB, fully differential current output stage

A true class ‘AB’ fully differential current output stage with very high common mode rejection ratio is presented in this study. The operational principle of this unique structure is discussed, its most important formulas are derived and its outstanding performance is verified by SPICE simulation in TSMC 0.18 μm CMOS, and Level49 technology. Owing to the elaborately arranged components, the proposed circuit demonstrates very high common-mode rejection ratio (CMRR), high slew rate, high current drive capability, high output compliance, and very low power consumption while operating at power supply of ±0.9 V. The interesting results such as current drive capability of ±100 μA, high output voltage swing of ±0.8 V, low static power consumption of 21 μW, and very high CMRR of 84.5 dB is achieved utilizing standard CMOS technology. The performance of circuit at the presence of process and voltage variations evaluated through corner case and Monte Carlo analysis. The harmonic distortion is evaluated to investigate the circuit’s linearity. The transient stepwise response analysis is also done to verify the stability of proposed class ‘AB’ FDCOS.     

ECG监护仪前置放大电路的设计

基于传统的仪用放大器基本框架,设计了一种新的可用于心电信号放大的前置放大器。在3 dB带宽范围内,该放大器的增益达到了48.3 dB。等效的输出噪声电压值为5.34 nV/Hz。根据生物电信号采集的特点,通过增加右腿驱动电路,提高了放大器的共模抑制比,对被测的生物体具有更安全的保护作用。仿真结果表明该放大器在增益、频率响应特性、共模抑制比等性能参数方面符合美国心脏协会(AHA)的建议要求,确保了输出心电信号的低失真,可用于ECG监护仪中。     

Low and midrange modulation frequency response for YBCO infrareddetectors: interface effects on the amplitude and phase

Bolometers were designed and fabricated from YBa₂Cu₃O_7-x films on MgO, SrTiO₃ , and LaAlO₃ substrates. Both the magnitude and phase of the IR-response of the detectors were investigated from 0.5 Hz to 100 kHz modulation frequencies, and from 0.8 to 20 micron wavelengths. Effects of the film-substrate thermal boundary resistance, R_bd, and the substrate-cold head thermal boundary resistance, R_s-c, were investigated. The effect of R_bd is shown to be significant in the response only at high frequencies, above 100 kHz. The response at low frequencies is found to be determined by R _s-c up to “knee” frequencies of 15, 60, and 600 Hz, for 0.05-cm thick SrTiO₃, LaAlO₃, and MgO substrates, respectively. A model for the bolometric response is developed, that correctly predicts the “knee” frequencies and the measured phase and amplitude of the response versus frequency up to about 10 kHz, including the predicted change from a f^-1 to a f^-1/2 dependence at the “knee” frequency. At the low bias currents used to operate the bolometers, Joule heating effects are negligible. From the model and experimental data, a specific heat of 0.59 J/K·cm³ has been deduced for LaAlO₃ at T≈90 K     

Frequency-dependent resistive and capacitive components in RFMOSFETs

It is found from measured high frequency (HF) S-parameter data that the extracted effective gate sheet resistance (R_gsh), effective gate unit-area capacitance (C_{gg, unit}), and transconductance (G_m) in radio-frequency (RF) MOSFETs show strong frequency dependency when the device operates at frequencies higher than some critical frequency. As frequency increases, R_gsh increases but C_{gg, unit} and G_m decrease. This behavior is different from what we have observed at low or medium frequencies, at which these components are constant over a frequency range. This phenomenon has been observed in MOSFETs with L_f longer than 0.35 μm at frequencies higher than 1 GHz, and becomes more serious as L_f becomes longer and the frequency higher. This behavior can be explained by a MOSFET model considering the Non-Quasi-Static (NQS) effect. Simulation results show that an RF model based on BSIM3v3 with the NQS effect describes well the behaviors of both real and imaginary parts of Y₂₁ of the device with strong NQS effect even though its fitting to Y₁₁ needs to be improved further     

Interpretation of SSM/I measurements over Greenland

Multispectral brightness temperature (T_B) measurements over Greenland are obtained from the Special Sensor Microwave Imager (SSM/I), which are flown aboard the DMSP satellites. This paper examines the different spectral characteristics over Greenland throughout the year. Although snow covers the vast majority of Greenland, the southern regions rarely exhibit the spectral characteristics associated with snowcover (i.e., T_B decreases at higher frequencies). In fact, the SSM/I polarization and frequency measurements over southern Greenland are more indicative of water than a snow-covered surface (i.e., T_B increases at higher frequencies). A simplified physical model is developed to help explain the anomalous measurements over southern Greenland. Model results indicate that high frequency radiation is mainly scattered by snow grains residing above the subsurface ice layers, whereas low frequency radiation is scattered throughout a much greater depth. Since low frequencies are scattered throughout a greater volume, they are depressed relative to high frequencies, and the typical snowcover signature is absent     

A novel ±0.5 V,high current drive,and rail to rail current operational amplifier

A current operational amplifier (COA) with very high current drive capability is presented in this paper. The principle of operation of this unique structure is discussed, its most important formulas are derived and its outstanding performance is verified by HSPICE simulation in TSMC 0.18 μm CMOS, BSIM3, and Level49 technology. Owing to the elaborately arranged components, the proposed circuit demonstrates very high frequency bandwidth, extremely high CMRR, high output impedance, and true rail to rail output voltage swing range while operating at very low power supply of ±0.5 V. The interesting results such as current drive capability of ±1 mA, high output impedance of 5 GΩ, wide gain bandwidth of 220 MHz, extremely high output voltage swing of ±0.45 V, which interestingly provides the highest yet reported output voltage compliance for current mode building blocks implemented by regular CMOS technology, low static power consumption of 159 μW, and very high CMRR of 155 dB is achieved utilizing standard CMOS technology. Full process, voltage, and temperature variation analysis of the circuit is also investigated in order to approve the well robustness of the structure. The transient stepwise and sinusoidal response analysis is also done to verify the proposed COA stability.     

Silicon dioxide breakdown lifetime enhancement under bipolar biasconditions

The authors point out that time to breakdown (t_BD) of silicon dioxide has a pronounced frequency dependence when it is measured under bipolar bias conditions. At high frequencies, bipolar t _BD, can be enhanced by two orders of magnitude over the t_BD, obtained using DC or unipolar pulse bias of the same frequency and electric field. The lifetime improvement is attributed to detrapping of holes. At high frequencies, the improvement is maximum because the trapped holes are concentrated at the interface where they can easily be removed upon field reversal. At low frequencies, there is less improvement because the trapped hole distribution extends further into the oxide. Two different mechanisms are proposed to explain the frequency-dependent spreading of the trapped hole distribution away from the interface     

Innovative Amorphous Silicon Balanced Ultraviolet Photodiode

An innovative balanced photodiode structure made in amorphous silicon/amorphous silicon carbide, suitable for detecting small current variations on a large background signal, is presented and characterized. The structure is a three-terminal device, constituted by two series-connected n-i-p photosensors, where the output signal is the difference between the currents flowing through the two diodes. The layer thickness and optical properties of the thin-film materials and the geometry of the structure have been optimized for the detection of ultraviolet radiation. Common mode rejection ratio (CMRR) values ranging between 30 dB at 254 nm and 42 dB at 365 nm have been measured, independent on the bias voltage. The decrease of the CMRR at lower wavelengths has been ascribed to differences in the surfaces of the two diodes exposed to the light.      

具有最优共模抑制性能的可变增益仪用放大器AD8221及其应用

目前市场上大部分仪用放大器的共模抑制比在200Hz处就开始衰减，因而难以满足某些设计要求，而美国ADI公司推出的增益可编程高性能仪用放大器AD8221，则能提供工业上最高的共模抑制比。AD8221在其增益为1时，能够在频率为10kHz处保持大于80dB的共模抑制比，因而能很好的抑制宽带干扰和线性失真。文中介绍了A138221的主要特点、工作原理以及引脚排列和功能，同时给出了AD8221的几种应用电路的设计方法。     

High-density MIM capacitors using Al2O3 andAlTiOx dielectrics

We have investigated the electrical characteristics of Al₂ O₃ and AlTiO_x MIM capacitors from the IF (100 KHz) to RF (20 GHz) frequency range. Record high capacitance density of 0.5 and 1.0 μF/cm² are obtained for Al₂ O₃ and AlTiO_x MIM capacitors, respectively, and the fabrication process is compatible to existing VLSI backend integration. However, the AlTiO_x MIM capacitor has very large capacitance reduction at increasing frequencies. In contrast, good device integrity has been obtained for the Al₂O₃ MIM capacitor as evidenced from the small frequency dependence, low leakage current, good reliability, small temperature coefficient, and low loss tangent     

Layered Al2O3-TiO2 compositedielectric resonators

Aluminium oxide displays a very low tanδ at microwave frequencies. It also possesses a remarkably high thermal conductivity, ideal for heat dissipation in high power satellite filters. However, its temperature coefficient of the resonant frequency (τ_f) is approximately 60 ppm/K. It is shown that the application of a film of titanium oxide which has a T_f of opposite sign (45O ppm/K) produces a composite in which the τ_f can be tuned to be zero over a wide temperature range. The tanδ of the composite at zero T_f is 3.3×10⁵ (Q=30000) at room temperature and at 10 GHz     

A novel fully differential biopotential amplifier with dc suppression

Fully differential amplifiers yield large differential gains and also high common mode rejection ratio (CMRR), provided they do not include any unmatched grounded component. In biopotential measurements, however, the admissible gain of amplification stages located before dc suppression is usually limited by electrode offset voltage, which can saturate amplifier outputs. The standard solution is to first convert the differential input voltage to a single-ended voltage and then implement any other required functions, such as dc suppression and dc level restoring. This approach, however, yields a limited CMRR and may result in a relatively large equivalent input noise. This paper describes a novel fully differential biopotential amplifier based on a fully differential dc-suppression circuit that does not rely on any matched passive components, yet provides large CMRR and fast recovery from dc level transients. The proposed solution is particularly convenient for low supply voltage systems. An example implementation, based on standard low-power op amps and a single 5-V power supply, accepts input offset voltages up to +/-500 mV, yields a CMRR of 102 dB at 50 Hz, and provides, in accordance with the AAMI EC38 standard, a reset behavior for recovering from overloads or artifacts.     

Operational amplifier with 1-V rail-to-rail multipath-driven outputstage

A bipolar operational amplifier (op amp) with a rail-to-rail multipath-driven output stage that operates at supply voltages down to 1 V is presented. The bandwidth of this output stage is as high as possible, viz, equal to that of one of the output transistors, loaded by the output capacitance. The output voltage can reach both supply rails within 100 mV and the output current is ±15 mA. The op amp is designed to be loaded by a 100-pF capacitor and the unity-gain bandwidth is 3.4 MHz at a 60° phase margin. The voltage gain is 117 dB and the CMRR is 100 dB. The frequency behavior of the multipath-driven (MPD) topology has an improved performance when compared to that of previously presented low-voltage output stages. A figure of merit F_M for low-voltage op amps has been defined as the bandwidth-power ratio     

Small-sized collector-up Ge/GaAs heterojunction bipolar transistorswith high gain, low base resistance, and high fmax

Small-sized collector-up Ge/GaAs HBT's are successfully fabricated and their operation at a high collector current density and at a high frequency is realized for the first time. The current gain of these devices reaches a peak value as large as 200 at a current density 6×10⁴ Acm^-2, and no degradation in the current gain is observed as the collector width is decreased down to 2 μm. The capability of lower voltage operation is also shown. Intrinsic and extrinsic base resistances are as low as 180 Ω/□ and 90 Ω/□, respectively. The calibrated values of f_T and f_max are 25 GHz and 60 GHz, respectively. The larger value of f_max compared with f_T might be attributed to low base resistance and low base-collector capacitance as expected from the collector-up structure     

Miniature Dual-Band Filter Using Quarter Wavelength Stepped Impedance Resonators

A miniature dual-band filter using quarter wavelength (lambda_g/4) stepped impedance resonators (SIRs) is proposed. Short and open SIRs are coupled together to realize lower and upper passbands, respectively. Miniaturization is achieved due to the use of lambda_g/4 resonators and a combline coupling structure. Two transmission zeros in a mid-stopband and one in each lower and upper stopbands are achieved. In order to see the capability of this structure to achieve different second passband frequencies, two dual band filters at frequencies of 2.45/5.25 GHz and 2.45/5.75 GHz are realized. Measured insertion losses are 1.3 dB and 2.3 dB and return losses are better than 17 dB and 18 dB at the first and second passband frequencies, respectively, with a mid-stopband attenuation better than 30 dB. The size of the filter is as compact as 19.0 times 5.2 mm² on a RO 4003C (epsiv_r = 3.38, h = 0.81 mm) substrate.