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A Quasi-digital QPSK Modulator Design for Biomedical Devices

For the biomedical transceiver, the data transmission is often asymmetric. At the downlink, the transceiver only needs to receive a simple command to control the operation of the external device, and the receiving data rate is low, about hundreds of Kb/s. However, data collected by external devices such as temperature sensors, pressure sensors, or cameras are often very large, which results in a transmitting data rate of several Mb/s. Therefore, a high energy-efficient modulator is needed. Compared with conventional digital modulator, analog modulator circuits have demonstrated superior energy efficiency at high data rates. This article presents a quasi-digital quadrature phase-shift keying (QPSK) modulator design realized by pure analog circuits which follows a logic design flow. The simulation results show that the system can generate a stable carrier of 64 MHz that meets intra-body communications (IBCs) requirements with a data transmission rate of 10 Mb/s. When the signal-to-noise ratios (SNRs) of the Gaussian channel is 14 dB, it can still maintain a bit error rate (BER) below 104.