For new generations of mobile communications devices, multiple standards will have to be incorporated. For example, UMTS will allow wide-area medium speed data connections, while GSM will provide speech and lower-rate data coverage in remote areas. For in-house, and increasingly also open-air use, the addition of WLAN compatibility will add high-speed data connections to the mix.
The A/D converter in the receive path is one of the key elements in such a device. A Sigma Delta converter is an attractive choice for a multi-standard solution, since speed can be traded for resolution. Nevertheless, covering multiple cellular and WLAN standards is a challenge, since the spread of bandwidth and resolution is very high. With these widely varying requirements, the digital decimation filter also has to provide a wide range of possible settings, while still achieving high performance and low power consumption. In the decimation filter, a maximum of flexibility is highly desirable, at least in the last stages, to allow for different post-processing approaches or to adapt to evolving standards.
In this project, a Sigma Delta converter covering GSM, UMTS and WLAN standards has been developed. Optimization options for maximum resource sharing and low power consumption are realized. The converter has been implemented in 0.18um CMOS to be compatible with fully integrated transceiver developments in mainstream technologies