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TitleA CMOS mixed-signal interface with a RF transmitter for a micromachined soil moisture sensor
Author(s)Morais, Raul
Valente, A.
Couto, Carlos
Correia, J. H.
Sigma - Delta
Soil-Moisture sensors
RF Transmitter
Issue date22-Jun-2003
CitationIEEE INTERNATIONAL SYMPOSIUM ON INDUSTRIAL ELECTRONICS, Rio de Janeiro, Brazil, 2003 – “IEEE International Symposium on Industrial Electronics : ISIE’03 : [proceedings]”. New Piscataway : IEEE, 2003. vol. 2. ISBN 0-7803-7912-8. p. 1-4.
Abstract(s)This paper describes a CMOS mixed-signal interface with a RF transmitter. This die is assembled in a Multi-Chip-Module (MCM) micro-system together with the micromachined soil moisture sensor to achieve a cost effective solution with accurate and reliable measurements for soil moisture in agriculture. The soil moisture probe, based on Dual-Probe Heat-Pulse (DPHP) method, is fabricated in bulkmicromachining technology. The DPHP method is based on the measurement of the maximum temperature rise at some distance from the heater, after applying a heat-pulse. The measurement of the temperature rise is obtained by subtracting soil temperature from the probe temperature. The mixed-signal interface is based on a pre-amplification stage and first-order sigma-delta modulator. The bit-stream output of the modulator is then applied to a counter as a first order decimation filter thus providing a 12-bit readout sample. Prior to transmission, data is encoded as a pulse width modulated (PWM) signal and then transmitted by means of an amplitude shift-keying (ASK) modulation. The transmitter features a VCO phase locked to the quartz crystal reference of 13.56 MHz to achieve a carrier frequency of 433.92 MHz. A RF power amplifier based on class E topology was chosen. The CMOS mixed-signal interface with a RF transmitter has been implemented in a single-chip using a standard CMOS process (AMI 0.7 µm, n-well, 2 metals and 1poly).
TypeConference paper
AccessOpen access
Appears in Collections:DEI - Artigos em atas de congressos internacionais

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