A 5-Gb/s 2.1–2.2-GHz Bandpass $\Delta \Sigma$ Modulator for Switch-Mode Power Amplifier

A tunable fourth-order bandpass
$\Delta \Sigma$
modulator (BDSM) designed and fabricated in 0.25-
$\mu$
m SiGe BiCMOS technology is presented. The designed modulator relaxes switching conditions for the amplification stage of the switch-mode power amplifier in comparison to the
${ f}_{ S}/4$
BDSM architecture. The BDSM is clocked at 5 GHz, while the notch frequency can be tuned in a range of 2.1–2.2 GHz. The modulator achieves 46.6-dB signal-to-noise and distortion ratio in 10-MHz bandwidth for a sine-wave input at 2.2 GHz consuming 330 mW from a
${-}$
3-V supply. The BDSM was also tested with a single-channel WCDMA signal. It has demonstrated 42.2-dBc adjacent channel leakage ratio at 5-MHz offset and less than 2.1% error vector magnitude over the tuning range.