Pulse Interval Modulation for biomedical wireless sensors

This paper presents a circuit capable of reducing the power used to transmit signals from implanted biomedical wireless sensors. Nowadays, Quasi-Digital sensors are an interesting option that satisfies key performances such as low voltage, low power, low cost, good accuracy and small die area [1]. Those sensors send out analog information using digital signals, either by changing their frequency, period or duty-cycle. In all of them, energy is consumed during the transmitter operation. We propose a power savings by reducing the period that the transmitter is turned on. The proposed circuit changes the square signal of a voltage to frequency converter (VFC) into shorter pulses, but keeping the frequency of the original signal. It generates a Pulse Interval Modulation - PIM signal to be transmitted. We implemented the circuit layout in IBM 130nm CMOS technology. Simulation results demonstrated the circuit work as expected, and the savings may reach over 80 percent.