Dynamic voltage and frequency scaling (DVFS) is a technique used to optimize energy consumption in ultra-low-power embedded systems. To ensure sufficient computational capacity, the system must scale up its performance settings. The objective is to conserve energy in times of reduced computational demand and/or when battery power is used. Fast Fourier Transform (FFT), Cyclic Redundancy Check 32 (CRC32), Secure Hash Algorithm 256 (SHA256), and Message-Digest Algorithm 5 (MD5) are focused functions that demand computational power to achieve energy-efficient performance. Selected operations are analyzed from the energy consumption perspective. In this manner, the energy required to perform a specific function is observed, thereby mitigating the influence of the instruction set or system architecture. For stable operating voltage scaling, an exponential model for voltage calculation is presented. Statistical significance tests are conducted to validate and support the findings. Results show that the proposed optimization technique reduces energy consumption for ultra-low-power applications from 27.74% to up to 47.74%.

This brief provides the mathematical analysis of the Schmitt-trigger propagation-delay influence on the asynchronous sigma-delta modulator (ASDM) output-signal frequency spectrum. Beside the propagation delay, the Schmitt-trigger slew-rate impact has been also presented. Based on the mathematical analysis, a method for the Schmitt-trigger propagation-delay compensation has been proposed. The method is implemented by introducing hysteresis-level modulation. The first-order ASDM simulation and measurement models have been proposed for the propagation-delay influence to the ASDM output-signal frequency and for the compensation method verification. The measurement and simulation results for the proposed method confirm the ASDM output frequency spectrum improvement.

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 (TEM). 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 multiuser coding. IPFM pulses trigger the Impulse Radio Ultra-Wideband (IR-UWB) pulse generator directly, providing two Ultra-Wideband (UWB) pulses per each IPFM pulse. Due to the lack of internal clock signal and microprocessor-free multiuser 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 μm CMOS technology. Measurement results of the IPFM transfer function for input voltage ranging from 0.15 V to 1.5 V 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 μW, while for the lowest input voltage it increases to 40.48 μW. The circuit occupies 0.14 mm $^2$ .