Hardware implementation of phased locked loop in biomedical diagnostics devices

Abstract

ABSTRACT. This paper is devoted to the implementation of synchronous demodulator of amplitude-modulated signals by means of digital signal processing to increase the amount of diagnostic information of biomedical devices. A feature of the implemented demo- dulator is the usage of a phase-locked loop system, which, while ensuring high sensitivity of the demodulator, allows processing signals with low power. To create a mathematical model of the demodulator being developed, a phase-locked loop structure chart was drawn up. When drawing up a block diagram of the PLL model, which in this case consists of a numerically controlled cosine-sine oscillator and a loop filter, it was taken into account that they operate in discrete time, i.e. the implementation of these schemes will be performed entirely in digital form. As a result of the calculation, the transfer characteristic and difference equation of the loop filter (proportional-integrating type) for second-order of phase-locked loop were obtained, and then the simulation of the calculated phase-locked loop system was carried out in the Simulink application in MatLab. Using the formulas obtained, a program was written to determine such loop transfer coefficients that can ensure the nominal operation of the phase-locked loop. The obtained simulation results confirmed that the developed version of the loop filter provides a wide capture band while simultaneously suppressing phase jitter. At the next step, a computer program was compiled in the Verilog language with the purpose of the full-scale implementation of the designed demodulator based on the field-programmable gate arrayt debugging board such as Spartan 6 Xilinx with the Xilinx ISE design system. In order to verify the developed software code for the hardware implementation of the demodulator in the Xilinx ISE design system, a software simulation of the input signal in Testbench with simultaneous use of the ISIM application was performed, and the simulation results were visualized in GTKWave. The obtained experimental results of the synthesized demodulator confirmed the results of simulation modeling