It is predicted that two fifths of mobile phone RF transceivers will be made using CMOS technology by 2009, so there is little surprise that semiconductor firms have started to put a big design effect behind the lower cost RF chip technology.
The shift towards CMOS front-end silicon in mobiles, FM radios and satellite receivers is driven by the cost benefits of using standard CMOS processes, but also offers the opportunity for closer integration with digital functions.
New chip design means that CMOS is replacing BiCMOS and SiGe technology in some cost-sensitive RF designs.
Philips Semiconductor, Infineon Technologies and Texas Instruments are all eyeing the RF CMOS market. But there are also a number of smaller specialists making an impact.
Peregrine Semiconductor, for example, uses silicon-on-sapphire substrates in its UltraCMOS process. Its PE42671 RF device is capable of switching between the two transmit channels in dual band W-CDMA and GSM mobile phones.
But RF CMOS is still a technology in the early stages of development and according to Rodd Novak, v-p marketing at Peregrine, “there is a need for the market to be educated as to what the technology can do”.
Silicon Labs already has an all-CMOS GSM/GPRS mobile phone chip, the AeroFONE Si4905, which integrates digital and analogue basebands and a quad-band RF transceiver. The PA, two crystals, SAW filters and antenna switch module are off chip. The firm has also introduced an FM tuner based on the CMOS process.
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SiLabs' FM tuner is fabbed on a CMOS process
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According to Tyson Tuttle of Silicon Labs, the design challenges being tackled are ensuring that phase noise is kept in spec and the ability to integrate the VCOs and PLLs. “The main factor is ensuring the margin of your design is sufficient for a mass production process,” says Tuttle.
TI’s interest in RF CMOS was indicated when it acquired Scandinavian CMOS RF specialist Chipcon a few months back.
It has an all-CMOS ZigBee wireless transceiver, the CC2430, which includes an 8051 MCU, ZigBee stack and IEEE802.15.4 software and full RF transceiver. The chip is made in 0.18µm CMOS process.
Like most of the larger chip firms, Philips has an established range of BiCMOS devices which provide RF functions in wireless comms and broadcast systems. But it too sees the cost benefits of all-CMOS designs as the high frequency performance increases with each process geometry shrink.
“As the CMOS process geometry nodes shrink you get a higher f(T) for free,” says Pietr Hooijmans, v-p for RF at Philips.
The move from 0.13µm to 90nm and even 65nm CMOS processes has operating frequency benefits, but it lowers the signal voltages which can be handled by the device. So a 0.13µm digital CMOS process is modified to have a thicker oxide layer which will support 2.5V and 3.0V transistors.
There is a similar need to modify the process at 90 and 65nm. According to Dan Rabinvoitsj, v-p of wireless products at Silicon Labs, at 65nm even operating voltages of 1V will be manageable.
However, it is worth pointing out that foundry United Microelectronics did not need to move to a 90nm process for a 192GHz VCO, which it fabbed on its 0.13µm RF CMOS process.