Digitally Optimized Delta-Sigma Modulator for WiMAX Transmitter Design

This paper proposes a new approach to reduce the sampling rate in delta-sigma (DeltaSigma) transmitters and, hence, to lower considerably the speed requirements of all critical digital circuit blocks. The proposed method relies on oversampling the signal by inserting zeros after the low-pass DeltaSigma-modulation and to use one of the harmonic outputs of the sampler instead of its fundamental. The optimum sampling frequency in terms of signal integrity and out-of-band performance is determined for this configuration through simulations. Using a sampling frequency of only 288 MHz, EVM and ACPR for a WiMAX signal with a bandwidth of 2 MHz around 2.45 GHz are 7 % and -55 dBc, respectively