1997-01-15 , E/DS-466/110

New 3 volt varicaps simplify tuning for mobile phone manufacturers so saving production costs

Philips Semiconductors has created a new range of varicaps that have been specifically designed for operation at 3 V in cellular phones, cordless phones and pagers. Until now, varicaps from TV tuners have been used in these applications but these have a spread of ±10% in the capacitance value, whereas the new Philips design has a maximum spread of ±5% and a typical spread of only ±3%. This much tighter capacitance specification means that manufacturers will find it much easier to compensate for the spread and thus save on production costs, especially as the surrounding circuitry does not have to be designed to be able to cope with such a large capacitance spread.

TV varicaps have to be designed to withstand a maximum of 30 V control voltage whereas a mobile phone only operates up to 3 V. Philips was therefore able to reduce the epitaxial layer accordingly as its thickness is directly proportional to the maximum voltage load that the device has to withstand. Much tighter controls were also introduced into the diffusion process to ensure that the doping profile (of what is essentially a diode manufacturing process) was very accurate as this is the direct cause of capacitance spread. The first product to be produced using this new process is the BB155, which achieves a capacitance spread of 45.2 to 49.8 pF at 0.34 V and 24.55 to 26.70 pF at 2.82 V, making it suitable for tuning applications requiring a capacitance ratio of two. In contrast, a typical TV tuner varicap has a capacitance spread of 43.0 to 49.0 pF at 0.5 V and 23.9 to 27.2 pF at 3.0 V. The BB155 can initially be used as a direct replacement for a TV tuner varicap in existing circuits, until they are adapted to take advantage of its tighter tolerances. It is available in a small surface mount SOD323. Prices are in the region of $0.12 in large volumes.

As Philips Semiconductors is currently developing the new smaller SOD523 package, there is also a space reduction roadmap for the future, which will provide a saving in board space that is always at a premium in portable devices.

Philips Semiconductors, a division of Philips Electronics NV, headquartered in Eindhoven, The Netherlands, is the eleventh largest semiconductor supplier in the world and the third largest supplier of discretes in the world. Philips Semiconductors' innovations in digital audio, video, and mobile technology position the company as a leader in the consumer, multimedia and wireless communications markets. Sales offices are located in all major markets around the world and are supported by systems labs.