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A novel procedure to approximate Wavelet bases using analog circuitry is presented. First, an approximation is introduced to calculate the transfer function of the filter, whose impulse response is the required Wavelet. Next, for low-power low-voltage applications, we optimize dynamic range, minimize sensitivity and fulfill sparsity requirements. The filter design that follows is based on an orthonormal ladder structure with log-domain integrators as main building blocks. Simulations demonstrate an excellent approximation of the required Wavelet base (i.e. Morlet). The circuit operates from a 1.2-V supply and a bias current of 1.2µA.

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The design of a 13.56 MHz/402 MHz autonomous wireless sensor node with asynchronous ECG monitoring for near field communication is presented. The sensor node consists of an RF energy harvester (RFEH), a power management unit, an ECG readout, a data encoder and an RF backscattering transmitter. The energy harvester supplies the system with 1.25 V and offers a power conversion efficiency of 19% from a -13 dBm RF source at 13.56 MHz. The power management unit regulates the output voltage of the RFEH to supply the ECG readout with VECG = 0.95 V and the data encoder with VDE = 0.65 V . The ECG readout comprises an analog front-end (low noise amplifier and programmable voltage to current converter) and an asynchronous level crossing ADC with 8 bits resolution. The ADC output is encoded by a pulse generator that drives a backscattering transmitter at 402 MHz. The total power consumption of the sensor node circuitry is 9.7 μ W for a data rate of 90 kb/s and a heart rate of 70 bpm. The chip has been designed in a 0.18 μm CMOS process and shows superior RF input power sensitivity and lower power consumption when compared to previous works.