Digitally-switched resonators for bandpass integrated transmission line ΣΔ modulators

A digital tuning approach for adjusting the frequency of a resonator in a bandpass integrated transmission-line based SDM (BP-ITLSDM) is presented. The resonators are tuned by switching the length of an integrated transmission line (ITL) instead of the conventional varactor tuning. It makes the compensation process for the finite gain bandwidth (GBW) of transconductances independent from the tuning process of the resonator. Additionally, the same resonator gain is achieved at different tuned frequencies. To reduce the effect of parasitics and digital control patterns, common mode signal switching (CMS) is employed. The simulations are performed for a 2.5GHz resonator using a 16-segmented switchable ITL with unit length of 430um. A frequency tuning range of 1.5GHz and a finite GBW compensating range up to half of the sampling rate 10GHz is achieved in a 0.25um BiCMOS SiGe technology.