Electronic Design
Chip Makes Two-Way Radios Easy

Chip Makes Two-Way Radios Easy

There are millions of two-way radios in use around the world. You might say they are a commodity item using legacy FM radio technology. And they continue to get heavy use despite the billions of cell phones now in use. Most of these radios are of the “handie talkie” variety. They are used by police, firefighters, EMS, dozens of other public services, state and federal agencies, and businesses, as well as the military.

There has been a concentrated effort lately to make radios that are spectrum-efficient so more radios can use the same bands now allotted to mobile radio. Previously sanctioned 25-kHz bandwidth channels have now been cut to 12.5 kHz in some systems, and 6.25-kHz channels are on the way. That means new technologies, both analog and digital. Freescale Semiconductor is addressing this challenge by offering a single-chip system-on-a-chip (SoC) radio to meet just about every two-way radio need in multiple markets using multiple protocols.

The Freescale MC13260 includes the RF transceiver, a software-defined modem, and an integrated ARM processor for all the control and related functions. It contains everything you need to implement a two-way radio except for some filters, a balun, a power amplifier, an antenna switch, and an optional low-noise amplifier (LNA) (see the figure). The MC13260 can save board space and cost while reducing time-to-market for new radios.

The RF transceiver is designed to operate over the 60-MHz to 960-MHz range. It has a built-in fully integrated fractional-N phase-locked loop (PLL) synthesizer. Also included are a 13-bit audio codec with analog I/O, three 12-bit digital-to-analog converters (DACs) for support functions, and a 10-bit general-purpose analog-to-digital converter (ADC) with four multiplexed inputs.

The receiver supports linear modulation, and the linear transmit support uses integrated I/Q DACs and an external modulator. A typical receiver spec has a sensitivity of –122 dBm in a 12.5-kHz channel. Other common specs include an adjacent channel selectivity of 75 dB, intermodulation rejection of 72 dB, and a blocker rejection of 90 dBc with 1-MHz offset. Transmit power is 5 dBm, which is sufficient to drive the 3- to 5-W external power amplifier.

The modem section of the chip is a full software-defined radio vector processor. It will do standard analog FM and dual-mode FM with digital voice/data. As for digital modes, it will handle DMR, P25, Tetra, and dPMR (see “Glossary of Digital Mobile Radio Terms” below). Incidentally, Advanced Encryption Standard (AES) processing is included on chip.

The internal processor is an ARM926EJ-S running at speeds up to 150 MHz, with 640 kbytes of on-chip RAM. The I/O on the processor is extensive and includes GPIO, SPI, SSI, I2C, two UARTs, and a keypad interface. There is a real-time clock, two pulse-width modulation (PWM) controllers, and two timers. A full-speed USB port with integrated an physical layer (PHY) is also available. The MC13260 operates from a nominal supply voltage of 2.775 V with its on on-chip low-dropout (LDO) regulators.

Samples of the MC13260 should be available in the second quarter of 2011 with production to customers in the first quarter of 2012.

Freescale Semiconductor


Glossary of Digital Mobile Radio Terms

DMR: Digital Modular Radio is a fully software-defined radio used by the military, primarily the Navy. It is designed to operate over the 2-MHz to 2-GHz range and can be programmed for any of a dozen or so waveforms or modulation types both analog and digital. It also features a wide range of voice and data encryption options.

dPMR: The Digital Private Mobile Radio standard is a four-level frequency shift keying (FSK) digital radio designed to operate in the new 6.25-kHz bandwidth channels. The transmission rate is 4800 bits/s with a codec rate of 3600 bits/s. It uses frequency division multiple access (FDMA) for access.

P25: Project 25, or APCO-25, is a suite of digital mobile radio standards for use in public safety and state and federal agencies in North America. It can operate in 12.5-kHz channels using a continuous four-level FM (C4FM) modulation scheme. Another option is compatible quadrature phase shift keying (CQPSK) that can be used in 12.5-kHz channels or 6.25-kHz channels. It supports DES, 3DES, AES, and RC4 encryption.

Tetra: Trans-European Trunked Radio is the digital mobile radio standard for Europe. It uses time division multiple access (TDMA) to transmit four users on one 25-kHz channel. Tetra uses π/4 – differential quadrature phase shift keying (DQPSK) modulation with a baud rate of 18,000 symbols per second or 36,000 bits/s.

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