Radio transceiver for 2.5G networks

Zarlink Semiconductor has unveiled an off-the-shelf, single-chip radio transceiver (transmitter/receiver) for cell phones used in multi-band, multi-mode, 2G and 2.5G digital cellular networks.

Zarlink’s ZL20250 is targeted primarily at handsets for GAIT overlay networks that add GSM capability and mobile Internet data services to existing TDMA/AMPS wireless infrastructure. Multi-mode GAIT cellular networks are being deployed extensively across North America.

Zarlink’s new transceiver eliminates about 60 separate components from GAIT cell phones, shrinking the size of the radio by more than half, and reducing BOM (bill of material) costs by up to 40%. The device supports the reception of all GAIT voice services, as well as data services based on the 2.5G GPRS and EDGE platforms. It also handles two-way data services at 384 kbit/sec – the top EDGE rate – without using external circuitry.

Zarlink’s transceiver supports full, two-way compatibility for 8PSK (8-level phase shift keying), the digital modulation scheme that gives EDGE its 384 Kbit/sec data rate. In addition, it supports the normal GMSK (Gaussian minimum shift keying) modulation technique used by GSM and GPRS applications.

The ZL20250 is also the first commercial single-chip, 2.5G cell phone radio transceiver. Traditionally, cellular receive and transmit functions have been implemented on two or more chips to ensure that sensitive RF front-end receive circuits are isolated from transmit signals. However, the ZL20250 integrates receive and transmit circuits on the same silicon chip by using a two-stage receiver design to overcome these isolation issues.

The chip’s receive circuitry has two IF inputs, one for GSM/GPRS/EDGE, the other for TDMA/AMPS. Incoming signals are mixed with synthesized LO (local oscillator) signals from an on-chip VHF VCO (very high frequency, voltage-controlled oscillator), amplified, and downconverted to the baseband frequency.

The ZL20250 receiver has integrated channel filters that allow the chip to connect directly to most baseband processors.

The transmitter on the ZL20250 is a highly linear circuit with a quadrature modulator, IF gain control, and a single-ended output. The single-ended output delivers enough power to directly drive a two-stage power amplifier, eliminating the need for an external balun (balanced/unbalanced) transformer.

The new chip also uses a fractional-N synthesizer to control its UHF (ultra high frequency) VCO, allowing it to switch rapidly between frequencies.

It operates in four key cellular frequency bands: 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz. This quad-band capability allows the transceiver to support TDMA/AMPS/GSM/GPRS/EDGE services in North America, as well as many GSM/GPRS/EDGE operating environments in Europe and other regions.

The chip is fully compliant with the TIA/EIA IS (interim standard)-136 specification, and with protocols for GSM, EDGE, and GPRS defined by ETSI.

The ZL20250 is now entering volume production. It is offered in a 56-pin MLP (micro-lead frame package) with dimensions of 8 mm x 8 mm. An evaluation board and API software support the chip. In high volumes, the ZL20250 is priced at less than $7.00.