An improved method and apparatus for using common mode feedback to
maintain a predetermined DC level for an intermediate frequency output
signal. A common mode feedback capacitor-select switch module is operable
to use a bandwidth control signal from a radio interface of a wireless
device to selectively connect a plurality of common mode feedback
capacitors to an operational amplifier, thereby generating a common mode
feedback signal as an input to an active mixer conversion gain module.
The predetermined combination of common mode feedback capacitors is used
in combination with a plurality of bandwidth capacitors to generate an
overall capacitance that maintains the bandwidth of the system at a
predetermined value. A predetermined capacitance value is "shifted" from
the bandwidth capacitor bank to the CMFB capacitor bank, thereby
providing an overall ratio that maintains the bandwidth while defining a
predetermined capacitance connected to the operational amplifier to
generate a desired common mode feedback signal that maintains the phase
margin of the output signal at a predetermined level.