Renesas Develops Bluetooth LE RF Transceiver Technologies that Simplify Board Design, Reduce Circuit Size, and Increase Power Efficiency

By Chad Cox

Embedded Computing Design

March 08, 2022

News

IoT devices need to provide flexible support for Bluetooth LE regardless of their implementation format. Renesas developed two technologies to address the requirements it has seen as needs in the IoT industry.

Renesas introduced its work on Bluetooth LE RF transceiver technologies with development in reducing the circuit area, including the power supply to 0.84 mm2. By modifying the receiver architecture, and reducing the number of inductors , Renesas has made enhancements such as a low-current baseband amplifier and a highly efficient class-D amplifier. to its Bluetooth LE transceiver. With power consumption of 3.6 mW and 4.1 mW during reception and transmission respectively, these advances enable smaller size, reduced board cost, and lower power consumption, while simplifying the board design process.

According to Renesas, the benefits of its new RF transceiver technologies are: 

Matching Circuit Technology Covering Wide Impedance Range (On-chip Antenna Impedance Tuner, AIT)

The integrated impedance-matching circuit technology presented by Renesas at ISSCC 2015 enabled compact and low-cost Bluetooth LE products that required no external inductors or capacitors for switching between reception and transmission or impedance matching. However, depending on the type of antenna or board design considerations, the impedance did not necessarily reach 50 Ω and an external matching circuit was still needed. In addition, when using the earlier technology and adding a matching circuit with impedance-changing functionality, issues involving increased signal loss and inability to achieve a sufficient range of variation could still arise.

To address these issues, Renesas has developed a new variable impedance-matching circuit technology that consists of two inductors and four variable capacitors. The transmitter-side inductor and receiver-side inductor used in the matching circuit are configured in a concentric arrangement, and their mutual induction is employed to reduce signal loss and cut the effective parasitic capacitance. This both expands the variable impedance range and substantially shrinks the circuit area. A voltage standing wave ratio (VSWR), which indicates impedance mismatches, equivalent to maximum 6.8 and a variable impedance range of approximately 25 to 300 Ω have been confirmed.

Reference Signal Self-Correction Circuit Technology Eliminating Need for Calibration Circuit (Self-IQ-Phase Correction, SIQC)

A reference signal (locally generated signal) of roughly the same frequency as that of the wireless radio signals received via the antenna is generated internally by the RF transceiver. The signal is used to convert gigahertz-band wireless signals to low-frequency baseband signals. The accuracy of the reference signal can be degraded by factors such as inconsistencies in the circuit elements or variations in the temperature or supply voltage. In the past, the compensation technology for phase and amplitude deviations with a calibration circuit was used to accurately generate the reference signal. This led to problems, however, because integrating such a calibration circuit required a larger chip area, higher power consumption, and increased test cost.

Renesas resolved these issues by developing a new self-IQ-phase correction circuit technology that uses reference signals of four different phases to correct each other by allowing the phase differences to cancel each other out. This self-correction circuit is much smaller and can be implemented at approximately one-twelfth the size of a conventional calibration circuit. The image signal rejection ratio, crucial to reception performance, averages 39 dB, which meets the Bluetooth standard with a comfortable margin to spare.

For more information, visit renesas.com.