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FROM EDN EUROPE: Silicon-on-sapphire hosts superior switches
by Graham Prophet -- EDN Europe, 10/13/2005
Peregrine Semiconductor builds RF CMOS chips using a process it calls UltraCMOS: it builds CMOS circuitry in epitaxial layers on a sapphire substrate. Freed from the parasitic capacitances that are inherent in devices built on a bulk silicon (semiconducting) substrate, UltraCMOS overcomes limitations in device operating frequency, non-linearities in RF behaviour, RF isolation, power loss and limited-Q resonant structures. Building CMOS on a non-conducting sapphire substrate also allows Peregrine to construct mixed-signal circuitry with significant amounts of control logic. The company's process further allows the company to integrate EEPROM with no additional mask steps.
In its latest products, Peregrine has implemented an upgrade it calls HaRP, (for "harmonic performance"). Further parasitic capacitances have been eliminated in device layouts-although the fundamental technology remains the same-to produce improvements in second and (especially) third-harmonic distortion, and in third-order intermodulation (IM3) performance. One of the first products to exploit the capability is an antenna switch designed for 3G cellphone handsets. The 42660 is a derivative and a drop-in replacement for the company's 4263 6-throw antenna switch, delivered in a flip-chip package for incorporation into RF handset modules. Peregrine's VP of Marketing Rodd Novak notes that 3G RF-front-ends present GSM-level technology with challenges in terms of linearity and IM3-a GSM phone operating in close proximity to a 3G handset could potentially cause a blocking signal in the WCDMA receive band, due to the intermodulation product, in the receive chain, of the two transmitter signals. The PE42660 will provide sufficient linearity through the antenna switch path to eliminate this possibility, Novak says. Its IM3 performance is 25 dB better than its predecessor and meets the 3GPP specification at all phase angles (between switch and duplexer), being under –110 dB for a transmit power level of 20 dBm. Third-harmonic figures are 20 dB better than before, measured with 32 dBm switched to a 50-Ω antenna load.
Other devices recently introduced in UltraCMOS include radiation-hard parts for military/satellite use; a 13-GHz pre-scaler, and a 6-bit digital attenuator.
Peregrine Semiconductor, www.psemi.com.
