Impedance Measurement Solution Based on the High Time Resolution DSP

Abstract

Efficient way to develop the almost-single-chip impedance measurement device is to use the off-the-shelf Digital Signal Processor (DSP) with the on-chip pulse-width-modulator(s) (PWM) to generate the multifrequency excitation signals, ADC to acquire the response (and optionally excitation) signals for further real-time Discrete Fourier Transform (DFT) for complex impedance estimation, DMA-controller for efficient data transfers in data acquisition etc.Such innovative and efficient in various aspects (cost, speed, accuracy) impedance spectrum measurement device, based on the TMS320F28069 DSP chip of Texas Instruments having close to 12-bit-resolution in 1MHz range and taking 1000 impedance spectras every second has been previously developed by the authors. Still, as shown here, the solution can be significantly improved by innovative using of the high-resolution timing features of the on-chip PWM modules - as well as for generation of the binary waveforms for the excitations with improved spectral content, as well as for precise control of timing of ADC sampling with uniform and non-uniform sampling schemes, improving the accuracy of the solution, by an order. Furthermore, the newer version of the similar DSP, like TMS320F28377 with enhanced multiple 16-bit ADCs with high-resolution PWM and having more digital processing power, helps further to improve the performance of the solution.