Digital generation of radio-frequency signals is a key concept of software defined radio. One of the main difficulties for multi-standard transmitter design based on Delta-Sigma (ΔΣ) modulators is to respect the different specifications in terms of out-of-band spurious emission. Focusing on the TX path of a UMTS/DCS1800 mobile phone, we propose hereinafter an efficient method aiming at synthesizing a complex 5th-order ΔΣ modulator which respects the targeted standards spurious specifications. The use of a complex noise transfer function allows a better optimization of noise shaping. In addition, this approach eases the reconfiguration of the modulator, and, it is a powerful tool for all order (real and complex) ΔΣ modulators synthesis, as it will be illustrated.

Keywords: Delta-Sigma modulator, Software defined radio.