Philips Semiconductors announced a highly integrated RF chip set aimed at designers of dual-band TDMA cellular (low-band) and PCS/DCS (high-band) phones. This chip set reduces the number of components needed to build a dual-band RF system by more than half. The SA1920 RF receiver front-end, the SA647 digital IF receiver, and the SA9025 transmit modulator with fractional-N synthesizer comply with the TDMA IS-136 standard for dual-band, dual-mode (AMPS/TDMA) operation. By the year 2001, it is expected that more than 50 percent of all new mobile phones will support dual-band operation.

The SA1920 RF receiver front-end integrates both cellular and PCS low noise amplifiers (LNA) and down conversion mixers. A PCS-band image reject mixer, however, eliminates the need for an external band pass filter between the LNA and mixer. An on-board doubler supports the use of a single external voltage-controlled-oscillator (VCO) for both cellular and PCS bands. In addition, the SA1920 includes control logic, power down mode circuitry, and input and output buffers to further reduce external glue components and improve ease-of-use. The SA1920 also supports multiple cellular (AMPS, TDMA, GSM) and PCS (TDMA, PCS1900, DCS1800) standards for multi-mode phones.

The SA9025 combines a 900 MHz transmit modulator with a 2.2 GHz fractional-N dual synthesizer and offset loop synthesizer on the same IC. The variable gain pre-driver amplifier delivers +10.0 dBm output power, which attenuates up to 46 dB in 0.18 dB steps. The dual synthesizer uses a fractional-N first local oscillator (LO) divider that operates to 2.2 GHz, providing fast switching in narrow-band applications. An integer type second LO divider operates up to 500 MHz. A third synthesizer provides the offset frequency needed between transmit and receive bands. The SA9025 also includes a three-wire serial interface for programming and power down modes. By using an external upconversion mixer, a PCS frequency signal can be obtained for high-band operation.

An IF receiver for portable digital and TDMA applications, the SA647 integrates an LNA, mixer, IF amplifier, IF limiter, fast receive signal strength indicator (RSSI) and oscillator in a single package. The LNA, integrated at the IF input, increases system sensitivity with improved noise performance. The SA647 has a RSSI dynamic range of 85dB and a system gain of more than 110dB.

One of the great things about this chipset (and there are many) is that it is multi-mode as well as dual-band. That means that it can be used in dual-band operations anywhere the cellular standard is one of AMPS, TDMA, or GSM and where the high-band standard is one of TDMA, PCS1900 or DCS1800. Although the single oscillator needed is still external to the chipset innovative ideas such as the PCS-band image reject mixer eliminate other external filter needs, and there has been considerable thought to eliminate other external functions, particularly on the front-end IC. On the transmit modulator an external mixer is also required for either the 1800 or 1900 high-band outputs needed. The alternate digital-channel approach using the SA647 is extremely tidy and at a price which makes it extremely attractive to the OEM designer.

These ICs are well thought out and have been an evolution from previous offerings. The market needs are well known to Philips and their successes with previous ICs bodes well for these parts. Although there is plenty of competition there is also a major expansion phase being entered into even with the problems in the Far East.

The SA1920 and SA9025 are both in a 48-pin plastic LQFP package, while the SA647 is in a 20-pin TSSOP. The SA1920 is priced at $3.32, the SA9025 is priced at $7.73 and the SA647 is priced at $2.38, in 10,000-piece lots. All three ICs are in production.