🔋 Ultra-Low-Power RF Transmitters

Overview

This project developed energy-efficient RF transmitter architectures for IoT and short-range wireless applications, powered by switched-capacitor DC-DC converters. The key insight is that traditional RF transmitters waste significant power in the PA supply regulation stage. By co-designing the DC-DC converter with the RF power amplifier (PA), the system achieves highly efficient supply modulation at the transmitter, dramatically reducing total power consumption.

Problem

IoT devices demand RF transmitters that operate at milliwatt-level power budgets while meeting spectral mask and EVM requirements. Conventional linear regulators powering the PA are highly inefficient, especially at back-off power levels. Switched-capacitor converters offer high efficiency but introduce supply ripple that degrades RF output spectrum and EVM if not carefully managed.

Approach

A co-designed switched-capacitor DC-DC converter and Class-E RF PA architecture was developed. The converter's switching frequency and phase were synchronized with the RF carrier to minimize supply ripple at baseband frequencies. An on-chip calibration loop compensated for converter output impedance variation. The signal chain is shown below:

The converter topology was optimized using GenAI-assisted engineering tools that rapidly explored capacitor bank sizing and switching sequences, reducing design iteration cycles significantly before committing to silicon.

My Contributions

• Designed the switched-capacitor DC-DC converter topology co-optimized with the Class-E PA
• Developed synchronization logic to suppress supply ripple at critical RF frequencies
• Simulated transmitter efficiency and EVM across power back-off levels
• Implemented on-chip calibration loop for converter output impedance variation
• Characterized prototype transmitter: efficiency, spectral mask, and EVM at 10 mW output

Results

• Demonstrated up to 70% power reduction vs. linear-regulator-based reference design
• Prototype operated at as low as 10 mW total power in characterization
• Extended projected battery life by approximately 2× in duty-cycled IoT scenario modeling
• EVM within specification for targeted short-range wireless standards

Tools & Stack

• CMOS process (node details withheld)
• Cadence Virtuoso / Spectre for circuit simulation (transient, PSS, Pnoise)
• Python for efficiency modeling and swept characterization data analysis
• Spectrum analyzer and RF power meter for transmitter output characterization
• GenAI-assisted engineering tools for converter topology exploration

Notes

Some circuit-level implementation details are withheld. Results reflect prototype characterization and simulation data.

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