Electronic Design

Silicon-On-Sapphire CMOS RF ICs Change Wireless System Design

Companies have been fabricating silicon on an insulating substrate for years. This approach lets IC designers make high-frequency, high-performance CMOS that can be used in fast processors or in RF and microwave circuits. The problem, though, is creating a process that can be implemented cost-effectively.

Some semiconductor vendors have succeeded with silicon-on-insulator. But the performance gains haven't matched what's achievable with silicon-on-sapphire. Peregrine Semiconductor's UltraCMOS process solves that problem. It produces CMOS RF circuits that equal and exceed the performance of gallium arsenide (GaAs), silicon germanium (SiGe), and other more exotic devices at lower cost.

With Peregrine's patented techniques, the standard bulk CMOS processes can be used to create ICs on the sapphire substrate. This virtually eliminates the problems associated with parasitic capacitances to the substrate and leakages that plague standard CMOS. The result is much higher frequency of operation, as well as unparalleled linearity.

Peregrine has achieved up to 100-GHz operation with CMOS with its 0.25-µm devices. In addition to getting very low-power operation, it's easy to integrate very high-Q inductors and capacitors with UltraCMOS. Coil Qs can reach as high as 50 at microwave frequencies. Super-fast digital circuits can be integrated directly on the same RF chip, too.

The PE4272 and PE4273 broadband switches exemplify UltraCMOS use (see the figure). These 75-Ω devices are designed for digital TV, PC TV, satellite/DBS TV set-top boxes, and selected infrastructure switching. With a single-pole double-throw format, they make a good replacement for PIN diode switching arrangements, greatly reducing the number of components while improving overall performance.

Both devices offer low insertion loss of only 0.5 dB at 1 GHz, P1dB compression of 32 dBm, and a high isolation of up to 44 dB at 1 GHz. They draw only 8 µA at 3 V and have a high electrostatic-discharge (ESD) tolerance of 2 kV. The PE4273 is housed in a six-lead SC-70 package and provides 35 dB of isolation. The PE4272 comes in an eight-lead MSOP and offers 44 dB of isolation. Prices for the PE4272 and PE4273 are $0.45 and $0.30 respectively in lots of 10,000.

The PE4263 single-pole six-throw switch, designed for four-band GSM handsets, has two transmit (TX) ports and four receive (RX) ports for a single antenna. It operates from 100 to 3000 MHz with an insertion loss of only 0.55 dB at 900 MHz and 0.65 dB at 1900 MHz. The TX-RX isolation is 48 dB at 900 MHz and 40 dB and 1900 MHz. The second and third harmonics are down by ?85 and ?72 dBc, respectively. The ESD isolation is 1500 V on all ports. No blocking capacitors are required. The 3-bit digital control and decoder is right on chip. The PE4269 is a die version of the PE4263.

Another slick example of the UltraCMOS process, the PE9308 rad-hard prescaler, offers a fixed divide-by-four ratio and operates up to 13.2 GHz. As a result, the device can be used in the popular X and Ku bands. It draws only 25 mA at 2.5 V, which is about one-tenth of an equivalent GaAs chip. Also, it can tolerate a radiation dose up to 100 krads. It suits use in phase-locked loops (PLLs) and synthesizers.

Peregrine Semiconductor

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