Anti-blocker design techniques for MOSFET-C filters for directconversion receivers

摘要

A linearized MOSFET-C low-pass filter suitable for a basebandnchannel selection filter for a direct conversion receiver is presented.nUsing polysilicon resistors instead of MOSFET resistors in the input andnoutput part, the filter achieves very high out-of-band linearity butnmaintains the original transfer function under the control of ancontinuous on-chip cutoff tuning scheme. In order to enhance thenlinearity of the triode-mode MOSFET variable resistors, the gates of thenMOSFETs are driven by a charge pump in the cutoff control loop. Also, annappropriate gain scaling is implemented to lower the input referrednnoise, thus making the out-of-band dynamic range wider. This fifth-ordernelliptic filter achieves -2 dBV in-band IIP3, +28 dBV out-of-band IIP3,n+94 dBV out-of-band IIP2 and -87 dBV input-referred noise, andndissipates 6.2 mW from a 2.7-V supply; the on-chip continuous automaticntuning system dissipates 4.1 mW