Pablo Aguirre

Ultra-low power CMOS cells for temperature sensors

Temperature sensors and voltage references require cells that generate both PTAT (proportional to absolute temperature) and NTC (negative temperature coefficient) voltages. We present a novel theoretical approach based on a quasi-constant current to obtain these voltages in standard CMOS technology using no resistors. A test circuit was fabricated in a 0.8 mum, CMOS process. We performed measurements in a 305 K to 375 K temperature range which verify the expected results. The circuit draws under 50 nA from a 1.6 V to 3.0 V supply

Experiences on analog circuit technology migration and reuse

This work deals with two aspects of the reuse and redesign of analog circuits. First, a method for technology migration of analog circuits, recently proposed by Galup-Montoro and Schneider (Proc. SBCCI2000, pp. 89-93, 2000), is validated experimentally in the redesign of a Miller OTA from a 2.4 /spl mu/m technology to a 0.8 /spl mu/m technology. In addition, the impact of the method on performance aspects of analog circuits not covered in the original proposal (slew rate and current mirror frequency response) is studied. As a second mechanism for allowing the reuse of analog circuits, the feasibility of the application of the reference bias current as a tuning parameter to customize the performance of an existing design to suit different applications is demonstrated.

CMOS op-amp power optimization in all regions of inversion using geometric programming

In this paper Geometric Programming is successfully applied to the power optimization of CMOS operational amplifiers using a model valid in all regions of inversion (weak, moderate and strong), which assures a true globally optimal design. A complete transistor model presents some problems on the formulation of the Geometric Program. We will show in this paper that in the case of power optimization, a careful analysis of the physical meaning of the conflicting model equations, allow us to overcome these problems in a simple and efficient way. The proposed algorithm is tested in several cases for a Miller amplifier, showing how the optimum inversion level spans all the inversion regions as the target bandwidth changes.

Bias circuit design for low-voltage cascode transistors

This article presents a design methodology for the most simple cascode transistors bias circuit, i.e. a diode-connected transistor, valid from weak to strong inversion. By taking advantage of a compact MOS transistor model, we show how the circuit can be easily designed to precisely fix the drain voltage of the cascoded transistor just above its saturation voltage. Test circuits were manufactured in a 0.35μm CMOS technology in order to test the design methodology under different operation regions (weak, moderate and strong inversion) and for long and short channel transistors. Standard deviation in measured drain voltage of the cascoded transistor is below 3% of its mean.

Design of a reusable rail-to-rail operational amplifier

This paper presents a reusable rail-to-rail operational amplifier. The unity-gain bandwidth can be tuned from 7.5 kHz to 1.5 MHz with total quiescent consumption ranging from 42 nA to 27.5 /spl mu/A with a 2 V supply voltage. A novel rail-to-rail architecture, proposed by Duque-Carrillo et al., and a low-power low-voltage class AB output stage, proposed by Silveira et al., are integrated to achieve an opamp that meets the requirements of a wide range of applications. A power optimization design methodology for a given settling time is explored and simulation results are presented.

Temperature controlled measurement system for precise characterization of electronic circuits and devices

A temperature controlled oven, with provisions for easy connection of instruments to the device under test, was designed and built. This paper describes the oven, its thermal model and control system and presents measurement results with different temperature profiles. An NTC thermistor measures the system temperature and a modified Steinhart & Hart equation is used to convert resistance readings to temperature. The system is capable of setting its temperature from just over ambient temperature up to 375K (around 102 °C). Temperature stability is ultimately limited by the resolution of temperature measurement to ±2mK.

SpectreHDL model of a photodetector cell for electrical simulation and its application in a WTA based light spot center location circuit

This paper presents a photodetector cell model hierarchically implemented in SpectreHDL. A typical photodiode electrical model is used and Gaussian distribution of the light spot through the pixels of the cell is implemented to estimate the amount of light power each photodiode receives. Light spot movement is also implemented in the photocell model to allow designers the validation of their signal processing circuitry. The model introduced here shows how analog hardware description languages can be used to combine different discipline systems in one model.