How Low Can You Go? New RF Transceiver IC Reaches 27 MHz (From 930 MHz)

By Jim Pomager
Senior Editor

In the increasingly congested transceiver integrated circuit (IC) space, new chips must clearly differentiate themselves from the competition... or risk being lost in the crowd. Some chipmakers bring ICs to market touting extremes in bandwidth, while others offer chips with enhanced flexibility. Still others claim advantages in package size. Melexis NV believes it has achieved gains in all three areas with its new TH71221 RF transceiver.

The TH71221 is a single-chip ASK/FSK/FM (amplitude shift keying/frequency shift keying/frequency modulation) transceiver IC designed for bidirectional half-duplex data transmission in the unlicensed ISM (industrial, scientific, and medical) and SRD (short-range device) bands. In stand-alone fixed-frequency mode, the transceiver can be used for an array of applications in the 300 to 930 MHz frequency range.

In programmable, frequency-agile mode, however, the TH71221 really distinguishes itself. Most transceiver ICs employ an internal voltage controlled oscillator (VCO), which restricts them to operation at 433, 868, or 915 MHz, for example. The TH71221, on the other hand, uses an external coil in combination with an internal varactor diode to tune the VCO to operate at frequencies as low as 27 MHz. According to Melexis, this 27-to-903-MHz operating range is the widest of any transceiver IC currently on the market.

Preset frequency steps at 315, 433.92, 868.3, and 915 MHz enable TH71221 users to jump between transmit and receive on these frequencies by simply toggling two pins. In addition, the IC incorporates a built-in linear FM detector that allows it to handle both analog and digital signals. And unlike most other transceivers, the TH71221 is capable of both ASK (on-off keyed) and FSK transmission and reception.

The TH71221 is housed in a low-profile 32-lead micro leadframe package (MLP) with a footprint of 5 mm by 5 mm. At this size, the transceiver is well suited for space-restricted applications, such as automobile two-way keyless entry devices. Other applications for the chip include: wireless networking, long-range RF tags, alarm systems, automatic meter reading, and remote sensors.

According to Dr. Andreas Laute, manager of Melexis' Wireless Communication Business Unit, the primary goal in developing the new transceiver was to simplify design for the RF systems engineers. "We not only wanted to provide them with superior performance and design flexibility, but also wanted to do so across all popular nonlicensed RF spectrums and other low-power broadcast formats," Dr. Laute said in a statement.

Melexis is currently offering engineering samples of the TH71221 and expects to be ready for volume shipments in early 2005.

For more information, contact Melexis.