1997-02-10 , E/DS-351/120

Philips Semiconductors has introduced a brand new range of high-performance low-voltage silicon bipolar RF transistors for use in the latest 1.8 GHz cordless and cellular telephones, proving that silicon solutions continue to provide the best price/performance ratios. Fabricated using a recently developed double-poly buried-layer process, the range currently includes small signal and medium power types with collector current ratings suitable for use in all stages of a mobile phone's RF transceiver, including its low-noise input amplifier, mixer, VCO and RF power amp driver. All types are optimised for use on 3 V supplies, but still perform well at supply voltages as low as 1 V. Typical applications for these transistors include DECT, PHS and DCS1800 telephone handsets, satellite receivers and pocket pagers.

"Our fourth generation devices had transition frequencies of 9.5 GHz and gains of 13 dB at 2 GHz," said Product Marketing Manager Paul Swinkels, "but these new fifth generation types feature double the fT, show gain improvements of between 5 dB and 8 dB, and noise figures at 2 GHz as low as 1.2 dB." "Their ultra-small SOT343 surface-mount packaging and specially designed internal leadframe help to ensure optimum RF circuit performance and a significant reduction in pc board area," he added.

Their transition frequencies (fT) of between 18 GHz and 22 GHz are an order of magnitude greater than the operating frequency of current wireless communication systems. When operated in common-emitter configurations at the optimum part of their gain-bandwidth characteristic, the small-signal types have gain values in excess of 20 dB at a VCE of 3.6 V and a frequency of 2 GHz. Medium power types achieve power gains in excess of 11 dB under similar operating conditions. These high gain figures mean that fewer stages are required in the telephone's RF amplifiers, resulting in reduced component count, lower power consumption and smaller handset designs.

Three small-signal types will initially be available, each optimised for low-voltage operation (from 3.6 V down to 1 V). The BFG403W, BFG410W and BFG425W have their maximum fT at collector currents of 3 mA, 10 mA and 25 mA respectively. They feature a gain of over 20 dB at 2 GHz and noise figures as low as 1.2 dB, allowing the design of telephones with the sensitivity required for good reception under all signal conditions. When used in mixer and VCO circuits, they provide the high gain and low phase noise required for stable operation. Capable of maintaining excellent gain at VCE voltages as low as 1 V, the BFG403W is ideal for use as a low noise amplifier in 900-MHz pocket pager receivers, where it can achieve noise figures as low as 1 dB.

The two medium power transistors in the range are the BFG480W and BFG21W, which have their maximum fT values at collector currents of 80 mA and 250 mA respectively. Their power gains at 2 GHz and 3.6 V are greater than 14 dB and 11 dB respectively. The power-added efficiency of these transistors is typically greater than 60%, facilitating the design of telephones with smaller battery packs and extended talk times. Both devices are suitable for use as driver stages in the RF power amplifiers of cellular telephones.

The BFG21W, in combination with a BFG425W, is capable of delivering the 500 mW output power required in DECT telephones. This 2-stage power amplifier achieves an overall power-added efficiency of over 50%. With the BFG21W operating at a slightly higher quiescent current, the amplifier is ideal for use in handsets that need excellent linearity performance, such as those designed for the Japanese PHS system.

The exceptionally high transition frequencies and gains of Philips Semiconductors' fifth generation RF Wideband Transistors have been made possible by a self-aligned, double-poly, buried-layer diffusion process that minimises base-collector (Miller) feedback capacitance and base resistance. At the same time, their top-side collector construction reduces series feedback and allows heat to be transferred via the emitter lead frame directly into the pc board's ground plane. Because no electrical isolation is required, overall thermal resistance between the transistor junctions and the pc board is typically less than 150 K/W (Kelvin per Watt) for medium power types.

In high volume the small-signal types sell for less than US$ 0.30 and the medium power types for less than US$ 0.45. Samples are available now.

The Discrete Semiconductors Business Group of Philips Semiconductors is the third largest supplier of discrete semiconductors in the world, with an annual turnover in excess of US$ 1 billion. The group's three main areas of expertise are RF products for mobile communications, video amplifiers for monitors and CATV applications, power semiconductors for automotive, industrial, lighting and EDP applications, and commodity semiconductors with a broad range of diodes and transistors. This broad product range makes the Discrete Semiconductors Business Group a global supplier to all major segments of the electronics industry. Sales offices are located in all major markets around the world and are supported by systems labs.