Interpolative pulse-shape filtering for a GSM/Bluetooth transmitter

We present an interpolative GFSK/GMSK pulse-shape filtering for wireless RF transmitters. The filter is software controlled to work in a multi-standard radio with an arbitrary reference frequency. The key benefit of this method is no requirement to generate a low-jitter baseband symbol clock, which is especially advantageous when the available reference frequency is not an integer multiple of the symbol rate. Instead, a high-jitter clock obtained by simple fractional-N digital division of the reference frequency is successfully used. The presented transmitter is realized without any analog filtering and is part of a single-chip fully-compliant GSM radio fabricated in a digital 90 nm CMOS process.