C. Azcona

12-b Enhanced Input Range On-Chip Quasi-Digital Converter With Temperature Compensation

This brief presents a monolithic 1.8-V 0.18-μm CMOS temperature-compensated voltage-to-frequency converter for sensor read-out interfaces in wireless sensor network applications. Measurement results show that the proposed converter features are suitable for an output frequency span of 2 MHz with an input voltage range of 0.1-1.6 V. This converter presents a relative error below 4.8% and a linearity error below 0.017% (i.e., 12 b) over the whole frequency span for a range of ( -40°C, + 85°C). Power consumption is 0.423 mW (20 nW in sleep mode), and it occupies an active area of 137 μm x 100 μm.

Low-Voltage Low-Power CMOS Rail-to-Rail Voltage-to-Current Converters

This paper presents three compact CMOS voltage-to-current converters based on OTA/common-source configurations, which attain rail-to-rail input-output operation. The three converters present a high impedance input node while provide a highly linear V-I relationship over a ( -40, +120°C) temperature range with a maximum transconductance temperature coefficient of 175 ppm/°C. Measurement results for 1.2-V 0.18- μm CMOS implementations confirm rail-to-rail operation with bandwidths of up to 14.5 MHz and THD of up to -50 dB for 1 Vpp at 100 kHz, active areas below 0.0145 μm2 and power consumption below 85 μW, which make these basic building blocks suitable for portable applications.

An ultra low-power low-voltage class AB CMOS fully differential OpAmp

This paper presents an ultra low-power class AB operational amplifier (OpAmp) designed in a low-cost 0.18 μm CMOS technology. Rail-to-rail input operation is achieved by using complementary input pairs with adaptive bias to enhance slew-rate. A class AB output stage is employed. For low-voltage low-power operation, the transistors both in the input and the output stage are biased in the sub-threshold region. The simulated DC open loop gain is 51 dB, the unity gain frequency is 40 kHz with a 65° phase margin and the slew-rate is 0.12 V/μs with 10 pF capacitive loads. A common-mode feed-forward circuit (CMFF) increases CMRR, keeping the DC gain almost constant: its relative error remains below 1 % for a (-40°C, +120°C) temperature range. The proposed OpAmp consumes only 1 μW at 0.8 V supply.

Precision CMOS current reference with process and temperature compensation

This paper presents a new first-order temperature compensated CMOS current reference. To achieve a compact architecture able to operate under low voltage with low power consumption, it is based on a self-biasing beta multiplier current generator. Compensation against temperature is achieved by using instead of an ordinary resistor two triode transistors in parallel, acting as a negative and a positive temperature coefficient resistor, that generate a proportional to absolute temperature and a complementary to absolute temperature current which can be directly added to attain a temperature compensated current. Programmability is included to adjust the temperature coefficient and the reference current magnitude over process variations. Results for a 0.18 μm CMOS implementation show that the proposed 500 nA reference operate with supplies down to 1.2 V accomplishing over a (-40 to +120°C) range temperature drifts below 120 ppm/°C.

Low-Power Wide-Range Frequency-Output Temperature Sensor

This paper presents a simple but effective linear frequency output temperature sensor based on a multivibrator current-to-frequency converter. Post-layout simulation results for a 1.2 V 0.18- μm CMOS design show high linearity over a temperature range from -40°C to +120°C, with an accuracy of ±1°C, a sensitivity of 354 Hz/°C and only 3 μW of power consumption, which makes the design suitable for portable systems.

A novel rail-to-rail differential voltage-to-frequency converter for portable sensing systems

This paper presents a new high performance 1.2 V - 0.18 μm CMOS differential voltage-to-frequency converter (dVFC). The proposed dVFC works properly over the whole differential common mode input providing an output frequency range of 0.0 - 0.9 MHz with 0.015% linearity error for a -40 to 120°C temperature range and a 30% supply voltage variation. Power consumption is below 65 μW, which makes it suitable to be used in portable applications.

A fully-differential adaptive equalizer using the spectrum-balancing technique

A low-voltage high-speed CMOS fully-differential adaptive equalizer based on the spectrum-balancing technique is presented in this paper. It was designed to compensate the strong attenuation of the transmitted signal due to fiber losses. The proposed equalizer, formed by a line equalizer and an adaptation loop, targets 2.5 Gb/s transmission for a simple NRZ modulation through a 50-m SI-POF. It was designed in a 0.18-μm standard CMOS process, fed with 1V and has a power consumption below 17.3 mW.

A compact low-voltage first-order temperature-compensated CMOS current reference

This paper presents the design of two new low-voltage first-order temperature compensated CMOS current references. To achieve compact topologies able to operate under low voltage with low power consumption, they are based on the simplest approach of cross-coupled current mirrors, and compensation is obtained by introducing a temperature dependent current mirror ratio. Results for 0.18 μm CMOS implementations show that the proposed 1 μA references operate with supplies down to 1 V showing temperature drifts below 238 ppm/°C over the (-40 to 120°C) range, which makes them suitable for low-cost portable applications.

A NDIR-based CO2 monitor system for wireless sensor networks

The ever-increasing application of wireless sensor networks in many different fields is causing a growing demand of low-cost energy-efficient sensors for monitoring physical variables such as temperature, pressure or gas concentration. This paper presents a conditioning system for low-cost non-dispersive infrared gas sensors used to measure the CO2 concentration in an open air environment. It mainly consists of an amplification and filtering circuit that adapts the small and noisy signal provided by the sensor to a signal which can be easily read by a low-power microcontroller. The proposed interface presents a good tradeoff between energy consumption and accuracy, compatible with the energy requirements of wireless sensor network applications. Test performed connecting the system interface to a node sensor in a wireless sensor network using a simple communications protocol only causes a 5% reduction in the operating life of the node.

A CMOS voltage-to-frequency converter with output frequency range programmability

This paper represents the design of a low-cost programmable CMOS voltage-to-frequency converter suitable for wireless sensor nodes signal conditioning. Designed in a 0.18µm CMOS technology supplied at 1.8V, it operates for a 0.0-1.6V input voltage with power consumption below 0.41mW. Three different output frequency ranges can be digitally selected: 0.0 to 0.5MHz, 0.0 to 1MHz or 0.0 to 1.5MHz. The accuracy achieved is better than 3 %, with linearity errors below 0.04 %.