Ring Oscillator BLE Transmitter for Low-Power Phase Noise Control
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Solution Overview
Problem
Bluetooth Low-Energy (BLE) transmitter designs face significant power consumption challenges, with the local oscillator (LO) and power amplifier (PA) accounting for over 80% of the power usage, limiting battery life in IoT devices and requiring further reduction in power consumption while maintaining phase noise performance.
Innovation Solution
An all-digital phase-locked loop (ADPLL) circuit with a ring oscillator and embedded time-to-digital converter, coupled with a frequency multiplier circuit using a windowed edge combiner, is employed to reduce power consumption and enhance phase noise performance, allowing for a sub-mW BLE transmitter compatible with standard asymmetrical communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LC voltage-controlled oscillators with high quality factors are used, then phase noise performance is improved, but power consumption increases significantly
Solution Approach 1:
The patent replaces the traditional LC voltage-controlled oscillator (analog/mixed-signal system) with an all-digital phase-locked loop system comprising a ring oscillator, time-to-digital converter, and digital control elements. This substitution of digital logic for analog oscillation generation achieves comparable phase noise performance while dramatically reducing power consumption to sub-milliwatt levels, as digital circuits operate at lower voltages and consume less static power.
Solution Approach 2:
The patent changes the operating parameters by using a ring oscillator with a lower quality factor but compensating through digital feedback control and time-to-digital conversion. The system accepts the higher inherent noise of low-Q digital oscillators and corrects phase errors digitally, thereby achieving good phase noise performance without the high power consumption associated with high-Q LC tanks.
2Duration of action of moving object
If power consumption is reduced to extend battery life, then device portability and battery life are improved, but phase noise performance deteriorates
Solution Approach 1:
The all-digital architecture replaces power-hungry analog components with digital logic elements that consume minimal power. The ring oscillator, time-to-digital converter, and digital phase accumulator operate at low voltages and frequencies optimized for battery life, while maintaining adequate phase noise performance for BLE communication through digital signal processing and feedback control.
Solution Approach 2:
The patent employs periodic sampling and measurement of phase errors through the time-to-digital converter, which periodically compares the oscillator output with a reference signal. This periodic digital measurement and correction approach allows the system to maintain phase coherence over extended periods on battery power, enabling long-duration operation with acceptable phase noise characteristics.
Data Source
AI summary
A Bluetooth Low-Energy (BLE) transmitter is presented for used in ultra-low-power radios in short range IoT applications. The power consumption of state-of-the-art BLE transmitter has been limited by the relatively power-hungry local oscillator due to the use of LC oscillators for superior phase noise performance. This disclosure addresses this issue by analyzing the phase noise limit of a BLE TX and proposes a ring oscillator-based solution for power and cost savings. The proposed transmitter features: 1) a wideband all-digital phase locked loop (ADPLL) featuring an fRF/4 RO, with an embedded 5-bit TDC; 2) a 4× frequency edge combiner to generate the 2.4 GHz signal; and 3) a switch-capacitor digital PA optimized for high efficiency at low transmit power levels. These not only help reduce the power consumption and improve phase noise performance, but also enhance the transmitter efficiency for short range applications.