LTE’s rollout in different bands around the globe generates a slew of new challenges for the ever-more complex mobile-phone RF front ends. Add carrier aggregation into the mix (“aggregating” two carriers together to increase the channel’s effective bandwidth to boost data rates), which leads potentially to a multitude of transmit- and receive-band combinations, and the complexity compounds even further. On top of that, there’s mounting pressure to reduce the RF front end’s form factor and footprint due to the larger batteries required by these feature-rich phones.
For a truly “global” mobile phone that can operate at all LTE frequency bands, the RF front end requires many different signal paths, with switches between these paths. Thus, the demand grows louder for RF switches with higher and higher throw counts.
Answering that call, Peregrine Semiconductor is leveraging its UltraCMOS CMOS-on-sapphire technology to create high-performance, high-throw-count switches. This process technology offers reduced bulk parasitics, high thermal conductivity, faster devices, improved linearity, and high passive Q versus bulk CMOS. The company revealed that it’s shipped more than one billion CMOS-on-sapphire RFICs, and that these chips have been designed into some of the most well-known smartphones. For example, recent teardowns of the iPhone 4S and other smartphones (performed by analyst Chipworks) confirm the presence of the company’s RF switches.
The billion-chip milestone was achieved with a new SP8T RF switch, one of several high-throw-count switches designed using the latest version of UltraCMOS. Peregrine says the release of this new UltraCMOS technology, called STeP5 (because it’s the 5th generation of its Semiconductor Technology Platform), has driven demands for UltraCMOS RFIC products to a record number of devices per week.
Peregrine’s latest SP8T switches support 4G LTE linearity and insertion loss over all conditions. Breaking it down, insertion loss equals 0.35 dB at 900 MHz and 0.45 dB at 1900 MHz; and linearity is: 2fo, 3fo equals -42 dBm at 824 MHz to 2.6 GHz. In addition, IMD2/3 is -111 dBm; isolation is 37 dB on all paths (900/1900 MHz); and there’s 4-kV HBM ESD (ANT) and 2 kV (all pins). The switches operate to 3 GHz.
Next on the agenda for the company is STeP6, which is expected to ramp-up later this year. Peregrine anticipates that it will continue the 23% year-on-year fall of RON * COFF of its switches (see the figure). STeP6 will be a 0.25-μm process, compared to STeP5’s 0.35 μm.
Furthermore, the company is still working with IBM to marry sapphire technology with IBM’s RF SOI standard process. Despite this work currently yielding inferior devices to STeP5, they refer to it as STeP7. Rodd Novak, Peregrine’s chief marketing officer, insists this work will continue on a parallel path to the company’s own process technologies.
Device-wise, Peregrine already makes antenna switches, multimode multiband (MMMB) switches and RF front end tuning devices. It expects to follow that with power amplifiers, and further down the road, tunable RF filters.