A 1.48-mW low-phase-noise analog frequency modulator for wireless biotelemetry

Area of Science:

• Electrical Engineering
• Biomedical Engineering
• Microelectronics

Background:

• Wireless biotelemetry systems require efficient and low-noise frequency modulators for accurate signal transmission.
• Accurate signal-to-noise ratio (SNR) estimation in frequency-modulated (FM) biotelemetry is crucial for reliable data acquisition.
• On-chip varactors are essential for tunable frequency generation in compact wireless systems.

Purpose of the Study:

• To present a low-phase-noise, hybrid LC-tank analog frequency modulator for wireless biotelemetry.
• To demonstrate the importance of accounting for large-signal oscillation effects on varactors for accurate SNR estimation.
• To validate the performance of a prototype frequency modulator integrated with a microelectrode for biopotential recording.

Main Methods:

• Fabrication of a prototype chip using a 1.5-microm CMOS process.
• Utilizing on-chip NMOS varactors in the inversion region as the frequency tuning element.
• Characterization of the voltage-controlled oscillator (VCO) for gain, phase noise, and power consumption.

Main Results:

• Achieved a measured gain factor of 1.21 MHz/V and phase noise of -88.6 dBc/Hz at 10-kHz offset from a 95.1-MHz carrier.
• Demonstrated a figure of merit (FOM) of -166.5 dBc/Hz with a power dissipation of 1.48 mW from a 3 V supply.
• Successfully interfaced the VCO with a microelectrode for wireless in vitro recording of a 50 Hz signal over 0.25 m.

Conclusions:

• The developed hybrid LC-tank analog frequency modulator offers high performance for wireless biotelemetry applications.
• Accurate SNR estimation requires considering large-signal oscillation effects on the varactor.
• The integrated system shows potential for sub-millivolt biopotential detection in wireless recording microsystems.