Importance

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Abstract

The present invention is a multimode sensor system that transmits power down a common bus coaxial cable typically using an alternating current power source. Each remote unit connected to the coaxial cable and through an isolation transformer converts the alternating current power to direct current power for an integrated circuit bus interface. The interface is connected to the sensors. The interface is externally pin programmable to provide a carrier at a frequency for a channel assigned to the remote unit. The carrier is provided by a ripple counter producing a frequency divided signal compared to a fixed reference frequency, where the result of the comparison controls a voltage controlled oscillator. When plural low frequency analog signals are to be transmitted over the common bus, an on-chip multiplexer multiplexes the signals to an off-chip, external analog-to-digital converter. The analog-to-digital converter loads an on chip parallel to serial register that applies each bit of the sampled signal serially to an on chip Manchester encoder. The encoder modifies the input voltage of the voltage controlled oscillator operating at the carrier frequency. The oscillator signal is applied to the coaxial cable. Receivers at the end of the coaxial cable are each tunable to a designated carrier frequency and each decode the respective encoded signal. If a high frequency analog signal is supplied to the voltage controlled oscillator, the carrier is modulated by the high frequency signal and the receiver demodulates the signal. The integrated circuit is arranged so that the digital circuitry is generally isolated from the analog circuitry so noise immunity is enhanced.

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First Claim