Research On Design Of Wireless Dual SAW Oscillator

The dual SAW(Surface Acoustic Wave) oscillator structure can eliminate the temperature and humidity interference from the environment, and improves the measurement accuracy of the measurand. The wireless dual SAW oscillator can realize the monitoring of the measurand, and the collected data will be received and transmitted wirelessly in order to reach to the goal of remote monitoring. Based on the ideas above, a novel scheme of wireless dual SAW oscillator is proposed in the paper.The scheme includes the dual SAW oscillator system and the wireless transmit-receive system. The dual SAW oscillator system consists of the two SAW oscillator circuits with the same structure and parameter, the mixer and the filter circuit. The transmitting section of the wireless transmit-receive system consists of the signal processing circuit, the frequency acquisition circuit and the wireless transmitting module. The receiving section consists of the wireless receiving module, the frequency acquisition circuit and the frequency displaying circuit. The low insertion loss SAW device with center frequency at 50.8MHz, the common collector amplifying circuit and the feedback network are incorporated into the SAW oscillator. The emitter bias is used to suppress the interference from temperature in the feedback network. The method with combination of hardware and software is used to process the outputted frequency signal of the dual SAW oscillator in the wireless transmit-receive system. The wave shaping circuit and the frequency dividing circuit are used to convert the sinusoidal signal to the square wave signal which can be collected appropriately by the microprocessor. The filtering algorithm is used to suppress the interference signal in the hardware circuit which can improve the accuracy of the signal acquisition.The output signal of the dual SAW oscillator system is tested, and the data results shows that the one track output frequency of SAW oscillator is 49.773 MHz, the other one is 50.613 MHz. The output difference frequency of the dual SAW oscillator system is 821.333 KHz, and the relative error is 2.23%. Meanwhile, both wireless transmit-receive system with and without filtering algorithm, when the input frequency is 100 KHz from 1 MHz, are tested and compared respectively. The relative error is 0.2% and 0.4%, respectively. The data shows that filtering algorithm can improve the accuracy of the signal acquisition in the wireless transmit-receive system.