Joint common mode voltage and differential offset voltage control scheme in a low-IF receiver

Direct RF sampling has recently been presented (K. Muhammad et al., Proc. IEEE Solid-State Circ. Conf, sec. 15.1, pp. 268-269, 527, 2004; K. Muhammad and R.B. Staszewski, Proc. IEEE Intl. Symp. on Circ. and Sys., sec. ASP-L29.5, 2004) in which an input RF signal is converted to current waveform, down-converted and integrated on a sampling capacitor. A rotating capacitor shares this charge with the sampling capacitor and transfers it to a subsequent discrete time switched-capacitor filter stage. In this paper, we present a mixed-signal approach for controlling the common mode voltage as well as injecting differential charge to compensate for the DC-offsets. This approach has been validated and incorporated in a commercial Bluetooth receiver IC realized in a digital 130 nm CMOS technology that meets or exceeds performance of other conventional Bluetooth radio architectures.