Wireless Systems Design

Radio-On-A-Chip Unwires Electronics

This 915-MHz Wireless Transceiver Offers A Simple, Low-Cost Means Of Delivering Radio Functionality To The Private Networks That Require Low To Medium Data Rates.

Many of today's engineers and designers hope to make the switch from wired electronics to their wireless counterparts. Factoring in installation, this migration typically provides a great deal of cost savings. But the adoption of wireless technology isn't always as easy as it sounds. The primary obstacle is that radio-frequency (RF) technology is a specialized field of expertise. It's not easily shared by all engineers and designers. How can a non-RF expert reap the benefits of wireless technology while at the same time mitigating risk? If the desired wireless solution will play in the 860-to-926-MHz frequency range, designers can now seek help from Honeywell International's HRF-ROC093XC radio-on-a-chip transceiver (FIG. 1).

Even if they have little or no experience in radio technology, this transceiver claims to help designers make the switch to wireless. It's well suited to digital voice and data applications in the home, office, or industrial setting. In those scenarios, monitoring is conducted from either a mobile or stationary point. The HRF-ROC093XC also can be utilized in applications as diverse as surveillance systems, medical-sensor communication, multi-node networks, and electronic gaming and toys.

For an embedded-microcontroller designer who wants to add wireless communications to an existing product, this transceiver promises a relatively simple and low-cost answer. Of course, it also is a viable solution for the radio-based products that are in need of a performance boost or cost reduction. Such devices might include thermostats, real-time industrial monitoring, modems, and two-way transceivers.

For its widespread applicability, the Honeywell HRF-ROC093XC radio-on-a-chip transceiver can thank an obvious source. As a fully integrated device, it features a smaller component count. It's therefore lower in cost than other older, discrete-based radios.

With the HRF-ROC093CX transceiver, for example, microcontroller functions that address and store the data have already been incorporated on chip. This approach lowers overall radio cost. It also reduces the workload of an external microcontroller, which is needed to communicate with the transceiver. As a result, operating the transceiver requires little more than a low-cost off-the-shelf microcontroller, an antenna, and a 2.5-V power supply. Cost savings also is derived from a streamlined design process, which is enabled by the Honeywell transceiver.

The HRF-ROC093XC is a 2.5-V, all-CMOS, programmable wireless transceiver. It's fabricated on a 0.25-µm process. On chip, it integrates an RF signal synthesizer, Frequency Shift Keying (FSK) transmitter, direct-downconversion receiver, and a digital interface (FIG. 2). It operates at data rates up to 128 kbps under license-free Federal Communications Commission (FCC) Part 15.247 and 15.249. The transceiver flaunts a range of 2000 ft.

Communication takes place on a single channel or on multiple channels for short-range applications. In applications where a longer range is desired, the transceiver can operate as a frequency-hopping spread-spectrum (FHSS) radio. In this scenario, the ability to use a higher transmit power and multiple channels vows to significantly reduce interference from other radios. To change frequencies or channels, the user only needs to write to one internal register. Honeywell even developed frequency-hopping software for its transceiver. It maintains communication synchronization and reliable message transfer.

Specific characteristics of the HRF-ROC093XC transceiver include an Rx sensitivity of −95 to −100 dBm with 6 dBm maximum of transmitter power. In transmit mode, the transceiver has a DC current of 30 mA. In receive mode, that current is 37 mA. The HRF-ROC093XC boasts 64-B FIFO on-chip data storage, a 32-b programmable message address, and an on-chip radio-frequency switch.

The HRF-ROC093CX was designed for simple, low-cost, private networks requiring low to medium data rates. It acts as an alternative to many sensor, modem, and control applications. Specifically, it targets those applications that don't require the high data rates (up to 1 Mbps) and complex multi-tier networking that's supported by other radio systems on the market, such as Bluetooth. Compared to radio systems that are currently available, this solution claims to provide longer range, lower power, and lower cost. It also demands less memory space for the protocol.

Although the on-chip integration of the RF synthesizer, RF switch, transmitter, and receiver is appealing, this characteristic doesn't differentiate this transceiver from other similar products on the market. Yet the HRF-ROC093XC does stand out for its ease of utilization in today's embedded products. For instance, the transceiver has been equipped with an enhanced digital-interface section. In addition to acting as a standard interface, that section minimizes processing and software development.

In particular, the HRF-ROC093XC's integrated digital functions and microcontroller interface allow it to be easily inserted into embedded applications. Examining this ease of use more closely, it becomes apparent that several features were added to the transceiver to reduce the microprocessor's workload. For starters, a Serial Peripheral Interface (SPI) bus or standard microcontroller interface constitutes the 6-MHz pipeline for control and data transfer between the transceiver and the microcontroller. This pipeline gives users control over operation through the transceiver registers. Control functions include transceiver-operating mode (Transmit/Receive/Sleep), RF operating frequency, transmitter power, data rate, Manchester Encode/Decode, and device or message address.

Tom Romanko, an Application Engineer at Honeywell, points to another feature that sets the HRF-ROC093XC apart. He summarizes, "In many other radio systems, the software performs much of the wireless data-formatting functions. This includes the formatting of messages, encoding and decoding data, and determining if a message was meant for that device. Since the data is usually in the 10-to-100-kbps range, this is a very inefficient use of processor resources." The HRF-ROC093XC transceiver integrates these functions on chip, thereby providing much greater efficiency. In fact, the Honeywell transceiver performs all of the packet-formatting and transmission functions. It will even Manchester Encode the data, attach a programmable 32-b address, append a preamble, and send the data to the modulator.

PRICE AND AVAILABILITY
The HRF-ROC093XC radio-on-a-chip transceiver is now available. Interested parties also can obtain Customer Demonstration Kits. In 100,000-unit quantities, the transceiver sells for $4. Overall, the bill of materials (BOM) has been shown to be 10%-25% less than many competing approaches when the HRF-ROC093XC is built into a complete radio with the external components.

Honeywell Solid State Electronics Center
12001 Highway 55, Plymouth, MN 55441; (800) 323-8295, FAX: (763) 954-2764, www.honeywell.com.

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