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dc.contributor.authorMorais, Raul-
dc.contributor.authorValente, A.-
dc.contributor.authorCouto, Carlos-
dc.contributor.authorCorreia, J. H.-
dc.identifier.citation"Sensors and Actuators A : Physical". ISSN 0924-4247. 115:2-3 (Sept. 2004) 376-384.eng
dc.description.abstractThis paper describes a wireless RF CMOS interface for soil moisture measurements. The interface basically comprises a Delta-Sigma (ΔΣ) modulator for acquiring an external sensor signal, and a RF section where data is transmitted to a local processing unit. The ΔΣ modulator is a single-bit, second-order modulator and it is implemented using switched-capacitors techniques in a fully-differential topology. With a sampling frequency of 423.75 kHz and an oversampling ratio (OSR) of 256, the modulator achieves a dynamic range of 98.7 dB (16.1 bit). The output of the modulator is applied to a counter, as a first-order decimation filter, and the result is stored. Prior to transmission, data is encoded as a pulse width modulated signal and assembled in a frame containing preamble and checksum control fields. This frame is then transmitted through a power amplifier operating at 433.92 MHz in class-E mode. To evaluate the ΔΣ modulator performance, the bitstream was acquired and transferred to a personal computer to perform digital filtering and decimation using MATLAB. The soil moisture sensor is based on dual-probe heat-pulse (DPHP) method and is implemented by using an integrated temperature sensor and a heater. After applying a heat-pulse for a fixed period of time, the temperature rise, that is a function of soil moisture, generates a differential voltage that is amplified and applied to the mixed-signal interface input. The described interface can also be used with other kinds of environmental sensors in a wireless sensors network. The CMOS mixed-signal interface has been implemented in a single-chip using a standard CMOS 0.7 μm process (AMI C07M-A, n-well, 2 metals and 1 poly).eng
dc.subjectWireless soil moisture sensorseng
dc.subjectSensor interfaceseng
dc.subjectsoil moisture sensorspor
dc.titleA wireless RF CMOS mixed-signal interface for soil moisture measurementseng
dc.subject.wosScience & Technologypor
sdum.journalSensors and Actuators A: Physicalpor
Appears in Collections:DEI - Artigos em revistas internacionais

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