 power amplification and an RFIC is also problematic with GSM as the excess heat generated by the PA can cause excessive drift in the small signal stages of the receiver, including baseband gain stages and filtering. At the lower levels of UMTS and LTE this becomes less of a problem but still requires careful implementation. The balance between these two options will be an important design consideration. The optimal trade off is very likely to be frequency specific. For example, if the design brief is to produce an ultralow-cost handset, then there are arguments in favour of integrating the RFPA on to the RFIC. However, this will make it difficult to integrate MEMS components onto the same device MEMS are also being suggested as potential replacements for present quartz crystal-based subsystems. The potential to use microelectrical mechanical resonators has been the subject of academic discussion for almost 40 years and the subject of practical research for almost as long. The problem with realising a practical resonator in a MEMS device is the large frequency coefficient of silicon, ageing, material fatigue and contamination. A single atomic layer of contaminant will shift the resonant frequency of the device. As with MEMS switches and filters, the challenge is to achieve hermetically robust packaging that is at least as effective as the metal or ceramic enclosures used for quartz crystals, but without the size or weight constraint. There are products now available that use standard CMOS foundry processes and plastic moulded packaging. While some 2G handsets make do with a lower-cost uncompensated crystal oscillator, 3G and LTE devices need the stability over temperature and time, accuracy and low phase noise that can only presently be achieved using a voltage-controlled temperature-compensated device. Temperature-compensated MEMS oscillators (TCMO), particularly solutions using analogue rather than digital compensation, are now becoming a credible alternative and potentially offer significant space and performa