INDUSTRY MICROELECTRONICS
Figure 1. Peregrine’s UltraCMOS 10 technology platform delivers significant performance enhancements, measured by the RonCoff figure of merit in fS.
alter feed points (by switching) and impedances (by switching, for example, shunt capacitances, into or out of the feed). Our digitally tuneable capacitors can realise this by supplying the necessary degree of control, offering 5-bit resolution, and delivering tuning ratios of as much as 7:1 with capacitances in the range of several pF. These properties, coupled with the high linearity UltraCMOS technology, enable the progression to a complete, reconfigurable RF front-end. On a conventional silicon substrate, a variety of parasitic effects manifest themselves. Parasitic capacitances exist between various parts of the active (and passive) devices, and in addition are voltage- dependent – doping profiles cause them to act as variable- capacitance junctions. Such effects are highly undesirable because they are inherently detrimental to linearity.
Building on an insulating substrate removes many of these effects at a stroke. In addition, as demonstrated by the antenna- tuning components alluded to above, as the technology is CMOS, adding control logic on the same die as the RF path is straightforward. For example, the stand-alone antenna tuning parts in our range offer standard SPI and MIPI RF front-end control interfaces.
Figure 2. Peregrine’s UltraCMOS Global 1 PA surpasses the leading GaAs PAs and exceeds the performance of other CMOS PAs by 13.5 percentage points. These figures are for the benchmark for PA performance of PAE (power-added efficiency) using a WCDMA (voice) waveform at an ACLR (adjacent channel leakage ratio) of -38 dBc.
of-merit for RF switches: The product of the on-resistance of the switch in its ‘on’ or conducting state, and the capacitance it presents in its ‘off’ state. The on-resistance determines the signal loss through the switched channel, so the smaller it is, the better. Meanwhile, the off-state capacitance sets the degree of isolation that the switch can provide; lower capacitance means lower signal leakage, so again smaller is better.
With our UltraCMOS 10 technology – the latest generation of a succession of technology steps that have employed diminishing feature sizes and constant refinements in performance – the key figure-of-merit formed from the product of on-resistance and capacitance in the off-state outperforms that of the closest competitive technologies by at least 30 percent (see Figure 1).
The objective of antenna tuning is to improve the impedance match between the PA output (or receiver input) and the antenna element itself. In smartphones, there are a variety of compact antenna forms, which are difficult to drive and often have to be used with a relatively high VSWR. These antenna also suffer from external loading effects.
One solution that can greatly improve the RF efficiency of the air interface and thereby, the battery life of the terminal, is to
Many of the same properties of UltraCMOS technology lend themselves to further integration. With freedom from parasitic capacitances and from stray conduction paths via the substrate, it is possible to realise a high degree of isolation between functional blocks – linear RF signal paths, and control logic – and between those blocks and interconnection paths. The remaining critical question, therefore, is this: Can a CMOS power amplifier be designed into an RF front-end and surpass the performance obtainable with a GaAs device?
Trumping GaAs With our development of the Global 1, that goal has been achieved. In terms of PA performance, no concessions have been made to a GaAs-based circuit. The incumbent technology, the GaAs-based PA, has dominated advanced handset air interfaces for some very good reasons: It can be designed to deliver the necessary power; it is broadband, with an individual
Figure 3. Peregrine’s UltraCMOS Global 1 PA enables performance optimisation through tuneable matching networks; band-specific tuning provides additional rejection to other frequency bands, which helps mitigate some of the difficult interoperability cases.
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www.compoundsemiconductor.net Issue VI 2014 Copyright Compound Semiconductor
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