The analog baseband receiver provides twelve filtering modes, a wide gain range, low noise, high linearity and integrated DC offset compensation. The filter can be configured as a complex poly-phase bandpass for low IF architectures giving image rejection, or as a low pass filter for direct conversion systems. It also has configurable bandwidth.
A 2nd order filter provides attenuation of close-in interferers. A third real low pass pole is incorporated to improve out of band rejection. A calibration block is used to calibrate all poles and zeros to within +/-3% of the nominal value. The baseband provides VGA functionality with a programmable gain range of +10dB to +24dB in 1dB steps.
An optional servo loop around the filter can provide continuous DC offset compensation in low pass mode and a high pass cut-off frequency of 1.5KHz over all gain settings.
An optional fast settling auto-zeroing DC offset scheme can be employed to reduce offset to acceptable levels in the guard time between time slots in a TDMA system. In polyphase asymmetric band-pass mode the filter’s transfer function means DC offset correction is not required.