Bluetooth 4.2 compliant SoCs reduce power consumption to 50%

In addition, the new Toshiba devices can reduce the power consumption to 50% of that of current products for IoT devices driven by a small-sized coin cell lithium battery while reducing the bill-of-material and required board space. They also support BLE 4.2 functions that are not available in many of the competitor devices.

Current consumption of 3.3mA for receive (RX) and 3.3mA for transmit (TX) are each achieved through an architecture and analogue circuit design suited to lower power operation. This considerably lengthens battery life. Toshiba’s SoC technology also integrates RF (Radio Frequency) matching networks. This eliminates the need for matching circuitry between the device and the antenna. The device also allows designers to eliminate capacitors that would typically be found alongside external quartz oscillators. This contributes to the downsizing of IoT devices by allowing the number of external components on the BoM to be reduced to just seven, delivering a further shrinkage in PCB circuit footprint by 20%.

Bluetooth low energy, developed specifically for low-power wireless communications, is used in many IoT devices to cut weight and extend battery life. In general, there is a trade-off between current consumption (for wearables current consumption in the range of 3-4mA is a major requirement) and radio performance (receiver sensitivity and transmission power). The company claims that conventional BLE SoCs cannot satisfy both requirements at once. Although it is effective to include external components in a BLE SoC to shrink the size of the Bluetooth low energy device, degradation of receiver sensitivity and transmission power of a BLE SoC with built-in RF matching networks remains a problem, due to loss mismatch.

Toshiba has introduced three techniques to reduce BLE SoC current consumption: a receiver architecture configuration suitable for low current consumption; a highly efficient power management system; and low current RF design.

1. The receiver architecture introduces a local synthesizer that employs a frequency half that of a conventional receiver, reducing current consumption in the local oscillator. Although the architecture tends to be vulnerable to interference signals because of its complex frequency configuration, a high tolerance to interference is achieved by adopting frequency planning that can avoid folding from cellular signals.
2. In order to improve power loss in the regulators (LDO: Low Drop Out), LDOs are eliminated from the SOC. As performance degradation due to switching noise from a DC/DC converter is a concern, a phase locked loop is used to fix the switching frequency of the DC/DC converter and prevent interference with the band used by the Bluetooth low energy.
3. In low current RF design, so that TX and RX can share a single Voltage Controlled Oscillator (VCO), the frequency tuning range of the VCO must be significantly wide, which increases current consumption. By dividing the VCO for the TX and the RX to narrow the required frequency tuning range for each VCO, low current consumption is achieved. In addition, a switching amplifier technique is introduced in the power amplifier to reduce current consumption.

By adopting these low current techniques, Toshiba’s BLE SoC technology reduces operating current consumption while improving radio performance; in the RX sensitivity is −93dBm and output power 0dBm. Furthermore, by integrating all RF matching networks in the SoC, which is fabricated with the 65nm CMOS process, the external component count can be reduced to seven from the 19 required by Toshiba’s current product.

The Toshiba BT4.2 devices are equipped with a full blown BLE 4.2 firmware asset. Unlike many other currently available devices, Toshiba’s BLE 4.2 SoCs can handle up to eight BLE connections simultaneously. As a result, they are suitable for use in Bluetooth Mesh and other multi-connection architectures. BLE 4.2 enhances security offering secure connections that are based on ECDH (Elliptic Curve Diffie-Hellman) public and private key cryptography, as well as link layer privacy for automatic private Bluetooth address generation and resolution and additional payload encryption – all functionalities that are not provided as standard in many other BLE ICs.

The BLE4.2 solution also features BLE Packet length extension to 251bytes from the 27bytes specified in the 4.1 standard. It provides for a theoretical speed improvement from 305 to 803kbps.

This technology was formally presented at the 2016 IEEE Asian Solid-State Circuits Conference (A-SSCC) in Toyama, Japan, on 8^th November. The company adopted the new current consumption technology in Bluetooth low energy products that started mass production in December 2016.