Optimization of the Data Rate of an OOK CMOS Medical Transmitter Based on LC Oscillators

This paper presents techniques for increasing communication data rates for OOK modulated signals in the case the carrier frequency is generated by a cross-coupled pair LC oscillator. The proposed circuitry completely turns off the transmitter during the transmission of "0" bit and oscillation occurs only when the data bit is "1" to reduce power consumption. The data bit controls the steady state bias current and the operation of the oscillator. The communication data rate is limited by the turn-on and turn-off time of the LC oscillator. In order to speed up the turn-on time of the oscillator, in addition to bias current, an extra current source is used during the build-up of the oscillator. The decay time of the oscillator when the data is switched from "1" to "0" is accelerated by shortening the inductor connections. The concept is demonstrated through the design of an LC VCO in 0.18 mu m CMOS technology. The LC oscillator is designed to oscillate in MedRadio band at 416 MHz frequency. Simulation results show that the proposed architecture shortens the turn-on time from 86.5 ns to 24 ns and the turn-off time from 101 ns to 5.93 ns. With the additional techniques, the maximum achievable communication data rate is increased by more than 6 times.