Wireless technology, according to its basic definition, is a way to use radio waves to replace wires. For many, the premiere wireless example is cellular communications. But wireless technology also has many shorter-distance, lower-power applications; the markets are vast for short-range wireless modules and integrated circuits (ICs) for such things as monitoring, remote control, and telemetry. These applications do not have the same bandwidth and data-rate demands as their better-known cellular counterparts, but they must consume extremely low power.
Standards developed for low-power wireless use include Wi-Fi (IEEE 802.11) and ZigBee (IEEE 802.15.4), both of which can operate in the unlicensed 2.4-GHz Industrial-Scientific-Medical (ISM) band (the same band as microwave ovens, cordless phones, and Bluetooth devices). ZigBee also makes use of other available unlicensed bands, such as 868 MHz in Europe and 915 MHz in the United States. Both standards operate by establishing simple low-power wireless personal area networks (WPANs) whether indoors or outdoors, with typically coverage distances of about 5 to 10 m and low data rates (less than 1 Mb/s).
Industry groups have grown large around these standards, including the WiFi Alliance (www.wi-fi.org); the ZigBee Alliance (www.zigbee.org), which supports low-power wireless applications for home automation, health care, smart energy, remote control, and telecommunications services; and more specialized manufacturer organizations, such as the HomePlug Powerline Alliance (www.homeplug.org) for monitoring power.
Although these are typically very low-power devices, they tend to be highly integrated. For example, the model ZiC2410 transceiver IC from California Eastern Labs (www.cel.com) was developed to run on a +1.5-VDC (battery) for automatic meter reading, medical patient monitoring, energy management, and home automation. This device is part of the company’s MeshConnect lines of ZigBee low-power wireless products, which also includes larger modules. The ZiC2410 transceiver IC can transmit as much as +8 dBm power at 2.4 GHz, requiring about 45 mA current, but it uses only about 4.6 mA in typical transmit/receive operation.
The chip is compliant with ZigBee IEEE 802.15.4 specifications and contains an RF transceiver with baseband modem, hardwired medium access controller (MAC), and embedded 8051 microcontroller. It is available in a 7 x 7 mm QFN or 5 x 5 mm VFBGA package. The transceiver circuitry includes a receiver low-noise amplifier (LNA), frequency synthesizer with phase-lock loop (PLL) and voltage-controlled oscillator, crystal reference oscillator, and transmit power amplifier. The receiver can provide -98 dBm sensitivity and supports ZigBee data rates to 250 kb/s, although the IC can also push data rates to 1 Mb/s for custom applications.
The on-board synthesizer exhibits typical phase noise of -81.9 dBc/Hz offset 100 kHz from the carrier and -108.6 offset 1 MHz from the carrier. The 16-MHz crystal reference oscillator has ±10 ppm crystal frequency accuracy. The chip employs offset-quadrature-phase-shift-keying (OQPSK) modulation for reliability and only requires 0.3 µA current in sleep mode.
This is impressive integration for a device that is intended for extremely low-cost applications, such as remote control light switches as part of the wireless automated home, or for patient-monitoring applications in hospitals. But it is only one of many such ICs designed for these applications, with performance requirements differing for other parts of the world depending upon availability of unlicensed frequency bands.
The model SX1231J transceiver from Semtech (www.semtech.com), for example, is designed to meet ARIB STD-T67 (426 to 470 MHz) and ARIB STD-T108 (915 to 930 MHz) requirements for use in Japan. It is suitable for remote-keyless-entry (RKE), active radio-frequency-identification (RFID), wireless sensor networks, and industrial monitoring and control. The ARIB STD-T67 standard specifies narrow 12.5-kHz channel spacing at about 426, 449, and 469 MHz, GFSK modulation, with power output limited to +10 dBm. The ARIB STD-T108 standard defines 200-kHz channels in the 915-to-930-MHz band.
Based on the firm’s TrueRF™ technology, the SX1231J transceiver is highly integrated, with a complete frequency-synthesized ultrahigh-frequency (UHF) transceiver capable of data rates to 300 kb/s using frequency-shift-keying (FSK) modulation. It includes a bit synchronizer for clock recovery and built-in temperature sensor and low battery indicator. It achieves receiver sensitivity of -120 dBm (and can maintain 1.2 kb/s at such low levels) with only 16 mA current consumption in receive mode and about 100 nA in sleep mode.
The IC includes a fractional-N frequency synthesizer with 61-Hz resolution and 32-MHz crystal oscillator; the synthesizer requires only 80-µs wakeup time from sleep mode to achieve a locked signal. The chip runs on voltages from +1.8 to +3.6 VDC and generates typical transmit power of +13 dBm, and as much as +17 dBm. Transmitter output power can be programmed in 1-dB steps from -18 to +17 dBm. The transmitter’s phase noise is typically better than -95 dBc offset 50 kHz from any carrier.
Silicon Labs (www.silabs.com) has developed a number of low-power RF transceivers for long battery life, including the recently introduced Si446x EZRadioPro® transceiver IC family for smart meters, security and home automation systems, industrial control systems, sensor networks, and electronic shelf labels. The devices offer continuous coverage from 119 to 1050 MHz using a variety of modulation formats, including frequency-shift-keying (FSK), Gaussian-minimum-shift-keying (GMSK), and on-off-keying (OOK) modulation. With transmit power levels reaching +20 dBm and receiver sensitivity to -126 dBm, the chips can achieve data rates to 1 Mb/s over an impressive dynamic range.
The transceivers employ a patented antenna diversity algorithm developed to counteract the effects of multipath and fading, effectively doubling the wireless range in a multipath/fading environment. They comply with Federal Communications Commission (FCC) requirements for use in the US but also meet ARIB specifications for Japan and ETSI requirements for Europe. The extended frequency coverage of the transceivers enables them to serve emerging narrowband applications such as the 151-MHz multiuse-radio-service (MURS) band in the US and the 138- and 169-MHz bands in Europe.
Designed for coin-cell battery-powered operation, the transceivers draw only 17 mA current at +10-dBm transmit power and about 13 mA current in high-performance receive mode. Mark Thompson, Vice-President and General Manager of Silicon Labs’ Embedded Mixed-Signal Products, says: “Silicon Labs’ Si446x family takes sub-GHz wireless technology to a new level of narrowband performance and power efficiency. We’ve set a new milestone in ultra-low-power operation for wireless transceivers, achieving 50 nA in sleep mode for the first time, making the Si446x transceivers an ideal solution for battery-powered and green energy applications.” The transceivers have a selling price starting at $1.57 in 10,000 piece quantities.
Analog Devices (www.analog.com) supports a wide range of low-power wireless applications, including in home automation and health-care monitoring. For example, its model ADF7023-J transceiver operates at ISM frequencies from 902 to 958 MHz (including the ARIB Standard T96 band at 950 MHz) with various modulation types. These include 2FSK, GFSK, MSK, and GMSK. The model can channel data rates from 1 to 300 kb/s. As with many of these highly integrated low-power RF transceiver ICs, it uses a fractional-N PLL/VCO-based frequency synthesizer with output channel frequency resolution of 400 Hz. To reduce spurious emissions, the synthesizer’s VCO operates at twice the fundamental frequency. The synthesizer is locked to an on-board 26-MHz crystal oscillator. Its phase noise is typically -116.3 dBc/Hz offset 600 kHz from the carrier and -126 dBc/Hz offset 1 MHz from the carrier.
The unique transceiver includes both single-ended and differential transmit power amplifiers, the better to accommodate transmit antenna diversity applications. The transmit output power can be programmed from -20 to +13.5 dBm. The programmable receiver provides IF bandwidths of 100, 150, 200, and 300 kHz. The ADF7023-J transceiver is designed for supplies from +2.2 to +3.6 VDC. It has only 12.8 mA current consumption in receive mode and 24.1 mA current consumption in transmit mode, with +10 dBm transmit output power. The transceiver, which is supplied in a 5 x 5 mm LFCSP package, is ideal for applications in IEEE 802.15.4g, smart metering, home automation, wireless healthcare, and wireless sensor networks. It even includes 128-b Advanced Encryption Standard (AES) encryption/decryption for security.
Infineon (www.infineon.com) also addresses sub-1-GHz low-power wireless markets with several IC product families, including its PMA 71xx SmartLEWIS™ MCU line of ADK/FSK transmitters with embedded microcontroller units (MCUs). Like the CEL transceivers, these highly integrated transmitters combine an on-board 8051 microcontroller with a high-efficiency power amplifier and advanced power control system, so as to minimize power consumption when using low-voltage battery power from +1.9 to +3.6 VDC. The device operates in the 315, 434, 868, and 915 MHz frequency bands using a PLL frequency synthesizer for tuning and ASK/FSK modulator for data rates to 32 kb/s. The transmitters, which include 128-b AES encryption, draw less than 0.6 µA in power-down mode. The firm offers a separate receiver IC for use in a transceiver system.
Texas Instruments (www.ti.com) offers its model C2500 transceiver for low-power wireless applications at 2.4 GHz. In a typical system, the CC2500 is used with a microcontroller and a few additional passive components. It operates from 2400 to 2483.5 MHz with a number of different modulation schemes, including OOK, GFSK, MSK, and 2FSK modulation, for data rates of 1.2 to 500.0 kb/s. It boasts -104 dBm receiver sensitivity with only 13.3 mA current consumption from a +3-VDC supply in receive mode and 250-kb/s data rate. The chip provides programmable output power to +1 dBm and features a PLL frequency synthesizer with 90-µs settling time and phase noise of -78 dBc/Hz offset 50 kHz from any carrier and -100 dBc/Hz offset 1 MHz from any carrier. The IC includes automatic frequency compensation (AFC) to align the synthesizer to the required receiver center frequency, as well as an on-board analog temperature sensor to maintain consistent performance with temperature. It draws only 400 nA current in sleep mode and is compliant with FCC, ETSI, and ARIB requirements for worldwide use. The transceiver is housed in a 4 x 4 mm QLP package.
In addition to devices developed for low-power wireless ZigBee and Wi-Fi applications, the ANT™ and ANT+™ specifications are proprietary wireless network protocols developed for use in the 2.4-GHz ISM band. Developed by Dynastream Innovations, Inc. [a wholly owned subsidiary of GPS receiver supplier Garmin (www.garmin.com)] as a higher-speed (to 1 Mb/s) variation of ZigBee, ANT is aimed at providing wireless functionality for sports products (such as fitness monitors). The ANT standard is supported by semiconductor suppliers like Nordic Semiconductor (www.nordicsemi.com) and Texas Instruments with low-power transceiver ICs. Nordic’s nRF24AP2-8CH device provides eight-channel ANT connectivity at 2.4 GHz. It includes the transceiver and a fully embedded ANT protocol stack for flexible serial interface with a wide range of external microcontrollers. The chip is designed for use with coin-cell batteries from +1.9 to +3.6 VDC and draws only 11 µA average current and less than 17 mA peak current during transmit mode. The device is supplied in a 5 x 5 mm QFN package. The firm also supplies an older, single-channel version of the chip, as well as several developer’s kits.