The Design Of Super Regenerative Receiver With High Frequency Selectivity

In recent years,with the increase of the IoT applications such as implantable medical treatment,outdoor remote sensing,and environmental monitoring,the demand for wireless receivers with high sensitivity,high frequency selectivity and low power consumption is growing.The super regenerative receiver opposes a highest figure of merit(FOM)than other types of receivers and thus becomes an important candidate meeting the requirements of these IoT applications.However,its poor frequency selectivity and weak anti-interference ability hinder its widespread application.In view of these,this article focuses on how to improve the frequency selectivity of super regenerative receivers and includes the following contents:1)The theoretical analyses on the frequency selectivity of super regenerative receivers.The mathematical model of the super regenerative oscillation(SRO)is established while the expression of SRO’s output voltage is deduced,and then the correlation between the frequency selectivity and SRO’s quench waveform is explained which shows that the quench waveform’s design parameters such as shape,frequency,duty cycle,peak voltage,etc.,can obviously affect the frequency selectivity of the super regenerative receiver.Meanwhile,the relationship between the pulse width incrementΔt of the comparator’s output in the super regenerative receiver and the receiving sensitivity is analyzed which concludes that the receiver sensitivity can be effectively improved when maximizing the amount of Δt by setting the comparator threshold voltage an optimal value.2)A super regenerative receiver with high frequency selectivity is proposed.A saw-tooth type of quench wave is selected based on the above theoretical analysis,and its frequency,duty cycle and peak voltage are optimized to improve the receiver’s frequency selectivity.A novel type of delay-sample demodulation circuit is presented which can overcome the shortcomings of traditional demodulation circuits such as high power consumption,high quantization noise,and low data rate.According to the research results of the correlation between the pulse width increment Δt and the sensitivity,an optimal threshold voltage of the comparator is carried out to improve receiver’s sensitivity.Finally,the super regenerative receiver is implemented with discrete devices such as BFR93 AW and the measurements are completed.As the measurement results show,the receiver can active a 0.2-MHz signal bandwidth while the saw-tooth quench signal frequency is 100 kHz,the duty cycle is 90%,the peak voltage is 1.1V,and the data transmission rate is 50 kbps.3)An auto-calibration circuit of the demodulation threshold voltage in the super regenerative receiver is proposed.In order to alleviate the fluctuation of the optimal threshold voltage caused by the process,voltage,and temperature(PVT),an auto-calibration circuit based on the above optimal threshold voltage theory is designed to maintain the threshold voltage.Using the principle of negative feedback,the auto-calibration algorithm can adaptively adjust the threshold voltage by comparing the comparator output’s pulse width.The auto-calibration circuit is implemented with a FPGA chip,and then stimulatingly and experimentally verified in Modelsim and Quartus Ⅱ.The experimental results show that the auto-calibration circuit works well and keeps the threshold voltage within the optimal range.The research results in this paper can be directly applied on the design of high-performance super regenerative receivers which lays a good technical foundation for promoting the application of super regenerative receivers in the Internet of Things such as implantable medical and outdoor remote sensing.