CAEN, France ( ChipWire)-- Despite being an early experimenter with direct-conversion RF transceivers for communications applications, Philips Semiconductors has nevertheless adopted a near-zero intermediate frequency (N-ZIF) architecture for its GSM transceivers.
The company has started sampling its first single-chip RF product for GSM applications, the UAA3535, based on the N-ZIF architecture.
The chip supports GPRS (General Packet Radio Service) Class 12 functions that allow data rates of as high as 56 kilobits per second. Class 12 refers to the ability to grab five time slots and assign as many as four of them to receive or transmit a signal.
Triple-band support for carrier frequencies at 900 MHz, 1,800 MHz and 1,900 MHz allows the same RF transceiver, and phones based on it, to cater to all European, North American and Far East GSM
requirements and roaming among the regions.
"Essentially it is a dual-band front end - 900 and 1,800 or 900 and 1,900 - but with a few additional components, a switch and wideband filter. It can be suitable for triple-band phones that
in 2000 will be in high demand," said Yvan Droinet, international product marketing manager for RF products at Philips Semiconductors.
Droinet said Philips Semiconductors would use the N-ZIF architecture to address future developments in GSM, such as Edge (Enhanced Data rates for GSM Evolution), and was likely to use it for third-generation (3G) phones that will operate with carrier frequencies just above 2 GHz.
"It is strictly for GSM at the moment, but it would be no problem to extend the architecture to 3G," he said. "We would certainly consider near-zero IF for GSM/GPRS/Edge first and then for a GSM/Edge/UMTS transceiver on a single die."
Philips said that it offers higher integration compared with traditional double-conversion superheterodyne receiver architectures, as well as advantages over direct conversion, also known as zero-IF.
A conventional IF configuration requires the use of an external SAW filter, while a single-conversion alternative can be implemented entirely on-chip.
"The intermediate frequency is 100 kHz, which provides an advantage in integrating the IF channel filter," said Droinet. "Compared with a zero-IF architecture, the advantage is that we don't need to do the calculations for the dc offset."
The UAA3535, which operates at 2.5 V, interfaces to standard A/D converters and requires few external components. Droinet said that apart from three VCOs, available as single components, the design only required a power amplifier, an RF antenna filter and three loop filters composed of four or five capacitors and some decoupling capacitors to complete the RF section.
The chip is being manufactured using Philips Semiconductors' 0.5-micron BiCMOS process. "The UAA3535 delivers all the advantages demanded by today's handset manufacturers, excellent features, a high integration level and low cost, for next-generation GSM mobile phones," Droinet said.
He said future iterations of its GSM chip sets will integrate new capabilities, such as Bluetooth, MP3and GPS, and will directly address 3G standards.
The UAA3535 single-chip RF transceiver is currently sampling, with volume production expected in July. It will be shown at the GSM World Congress in Cannes, France, Feb. 2-4.