A reconfigurable acoustic telemetry transmitter employing crystal-less temperature-independent frequency reference for oil drilling applications

Abstract

A reconfigurable acoustic telemetry transmitter employing crystal-less temperature-independent frequency reference has been realized in 1&181m SOI CMOS process for oil drilling applications. The transmitter can be configured to transmit either 3-channel chirp signal or 6-channel OOK signal with achieving data rate of 60bps and 120bps, respectively. Different frequencies derived from the frequency reference are directly modulated by input data before being combined and sent through a multiple feedback low pass filter. Two different approaches have been proposed to realize the frequency reference. The first approach is implemented through a frequency-locked loop employing RC phase shifter with resistor temperature coefficient compensation technique. It achieves a frequency inaccuracy of ?1.94&37 over the temperature range of 175&176C to 275&176C. Then a temperature-independent switched capacitor based frequency-to-voltage converter which is incorporated within FLL is exploited. The FLL provides the frequency inaccuracy of ?2.85&37 over the temperature range of 25&176C to 300&176C using digital trimming.