An Energy Efficient Multi-User Asynchronous Wireless Transmitter for Biomedical Signal Acquisition

The paper presents a novel transmitter architecture for short-range asynchronous wireless communication, applicable to simultaneous multi-user wireless acquisition of biological signals. The analog signal, provided from an analog biosensor, is transformed to time information using an Integral Pulse Frequency Modulator (IPFM) as a Time-Encoding Machine. The IPFM generates a time-encoded unipolar pulse train, maintaining the linear dependence of the output pulse distance on analog input voltage. The system enables continuous acquisition of the signals from multiple sensors in which each transmitter has unique feedback loop delay used for multi-user coding. IPFM pulses trigger the Impulse Radio Ultra-Wideband pulse generator directly, providing two ultra-wideband (UWB) pulses per each IPFM pulse. Due to the lack of internal clock signal and microprocessor-free multi-user coding, the circuitry satisfies the requirements of multi-user coding energy efficiency and size reduction, which are crucial demands in biomedical applications. The proposed Time-Encoded UWB (TE-UWB) transmitter is implemented in 0.18 <inline-formula><tex-math notation="LaTeX">$\mu{\text{m}}$</tex-math></inline-formula> CMOS technology. Measurement results of the IPFM transfer function for input voltage ranging from 0.15 to 1.5 <inline-formula><tex-math notation="LaTeX">${\rm V}$</tex-math></inline-formula> are presented, providing the dependence of the IPFM pulse time distance on analog input voltage and power consumption dependence on the input voltage level. For continuous monitoring operation, total power consumption of the transmitter circuitry for the maximum input voltage is 10.8 <inline-formula><tex-math notation="LaTeX">$\mu{\text{W}}$</tex-math></inline-formula>, while for the lowest input voltage it increases to 40.48 <inline-formula><tex-math notation="LaTeX">$\mu{\text{W}}$</tex-math></inline-formula>. The circuit occupies 0.14 <inline-formula><tex-math notation="LaTeX">${\text{mm}}^2$</tex-math></inline-formula>.