J. Galan

A free but efficient low-voltage class-AB two-stage operational amplifier

A simple and efficient low-voltage two-stage operational amplifier with Class-AB output stage is introduced. It has a large effective output current boosting factor (/spl sim/50) and close to a factor 2 bandwidth enhancement. This is achieved at the expense of minimum increase in circuit complexity and no additional static power dissipation. Experimental verification of the characteristics of the proposed circuit is provided.

A low-power low-voltage OTA-C sinusoidal oscillator with a large tuning range

A new operational transconductance amplifier and capacitor based sinusoidal voltage controlled oscillator is presented. The transconductor uses two cross-coupled class-AB pseudo-differential pairs biased by a flipped voltage follower, and it exhibits a wide transconductance range with low power consumption and high linearity. The oscillator has been fabricated in a standard 0.8-/spl mu/m CMOS process. Experimental results show a frequency tuning range from 1 to 25 MHz. The amplitude is controlled by the transconductor nonlinear characteristic. The circuit is operated at 2-V supply voltage with only 1.58 mW of maximum quiescent power consumption.

Super Class-AB OTAs With Adaptive Biasing and Dynamic Output Current Scaling

A new family of single-stage super Class-AB operational transconductance amplifiers (OTAs) suitable for low-voltage operation and low power consumption is presented. Three novel topologies are proposed featuring simplicity and compactness. They are based on the combination of adaptive biasing techniques for the differential input stage and nonlinear current mirrors for the active load that provide additional dynamic current boosting. The OTAs have been fabricated in a standard 0.5-mum CMOS process. Experimental results show a greatly improved slew rate by factors 30-60 and gain-bandwidth product by factors 11.5-17 when compared to a classical Class-A OTA. The circuits are operated at plusmn1-V supply voltage with only 10 muA of bias current

Comparative analysis of buck-boost converters used to obtain I–V characteristic curves of photovoltaic modules

In this paper, the usefulness of several topologies of DC-DC converters for measuring the characteristic curves of photovoltaic (PV) modules is theoretically analyzed. Eight topologies of DC-DC converters with step-down/step-up conversion relation (buck-boost single inductor, CSC (canonical switching cell), Cuk, SEPIC (single-ended primary inductance converter), zeta, flyback, boost-buck-cascaded, and buck-boost-cascaded converters) are compared and evaluated. This application is based on the property of these converters for emulating a resistor when operating in continuous conduction mode. Therefore, they are suitable to implement a system capable of measuring the I-V curve of PV modules. Other properties have been taken into account: input ripple, devices stress, size of magnetic components and input-output isolation. The study determines that SEPIC and Cuk converters are the most suitable for this application mainly due to the low input current ripple, allow input-output insulation and can be connected in parallel in order to measure PV modules o arrays with greater power. CSC topology is also suitable because it uses fewer components but of a larger size. Experimental results validate the comparative analysis.

Different methods to obtain the I–V curve of PV modules: A review

In order to characterize photovoltaic devices a procedure to measure I–V curves is required. The main methods used to perform this task are reviewed. It is shown that at least six distinct methods have been reported in the literature with many variations in implementation. A detailed comparison taking into account typical parameters for measuring systems is accomplished. This paper could be used as a reference for future work on photovoltaic module characterization.

Tunable Linear MOS Resistors Using Quasi-Floating-Gate Techniques

A family of tunable MOS resistors based on quasi-floating-gate (QFG) transistors biased in the triode region is analyzed in this paper. From the study results, a new device that outperforms previous implementations, is presented. By means of a capacitive divider, the ac component of the drain-to-source voltage scaled with a factor alpha les 1 is added to the gate-to-source voltage leading to a cancellation of the nonlinear terms. The effect of alpha on resistor linearity is analytically studied. Simulation results are also provided for different technologies. Finally, a complete transconductor has been built which preserves the linearity of the MOS resistor. Three versions of the transconductor have been fabricated for different values of alpha (alpha = 0, 0.5, and 1) in a 0.5 mum CMOS technology with plusmn1.65-V supply voltage. Experimental results show (for alpha = 1 ) a THD of - 57 dB (HD2=-70 dB) at 1 MHz for 2-V peak-to-peak differential input signal with a nominal ac-transconductance of 200 muA/V and a power consumption of 3.2 mW.

A Tunable Pseudo-Differential OTA With

A novel linear tunable transconductor based on a combination of linearization techniques is presented. The input signal is transferred to the V-I conversion element by means of a high-speed feedback loop. Then, the linear V-I conversion is accomplished using quasi-floating-gate MOS transistors biased in the triode region. Finally, the absence of current mirrors in the signal path provides low sensitivity to transistor mismatch and reduces the harmonic distortion. The operational transconductance amplifier (OTA) was fabricated in a 0.5-mum CMOS technology with a single 3.3-V supply voltage. Experimental results show a total harmonic distortion of -78 dB at 1 MHz with 1-Vpp input signal. High linearity of the OTA is obtained over a two octave tuning range with only 1.25-mW power consumption.

-78~{\hbox {dB}}

A Gm-C third-order Chebyshev low-pass filter with a novel switched capacitor frequency tuning technique for a zero-IF Bluetooth receiver has been designed. The frequency tuning scheme is simpler and has more relaxed specifications than conventional ones. Furthermore, a highly linear pseudo-differential transconductor with a compact feedback loop able to operate with low supply voltage has been used. This control loop holds the input transistors in triode region and provides high output resistance, keeping high linearity in a wide range of transconductance. The filter bandwidth is 0.5 MHz and the overall scheme consumes 1.1 mA from a 1.8-V supply. The measured third-order intermodulation (IM3) distortion of the filter for a 1 Vpp two-tone signal centered at 300 kHz is -65 dB.

THD Consuming 1.25 mW

A new experimental way to measure the I-V characteristic curve of a solar cell, module or photovoltaic generator by using Buck-Boost-Derived DC-DC converters is proposed. Theoretical analysis shows that the optimal topologies for this purpose are the SEPIC (Single-Ended Primary Inductance Converter) and Cuk converter. The advantages of this method are described, and experimental results show its usefulness.

A Very Linear Low-Pass Filter with Automatic Frequency Tuning

A low voltage two stage operational amplifier with class AB output stage is presented, featuring simplicity and efficiency. It has a large effective output current boosting factor (~50) and close to a factor 2 bandwidth enhancement. This is achieved at the expense of minimum additional circuitry with no extra static power dissipation. Experimental verification of the characteristics of the proposed circuit is provided