An Image Frequency Rejection Filter for SAW-Less GPS Receivers

We have developed an on-chip RF filter in 130 nm BiCMOS for SAW-less GPS receivers. The filter is implemented as a cascode amplifier stage with reactive resonant tanks. The filter employs two Q-enhanced LC tanks to create a transfer function with steep roll-off characteristic and narrow passband. The image rejection filter achieves a 3 dB bandwidth of less than 12 MHz at the GPS L₁ center frequency of 1575.42 MHz. The resulting magnitude response exhibits a notch at 1540 MHz and at 1610 MHz, attenuating noise and interference 30 MHz away from the center frequency by more than 30 dB. The NF of the RF filter is 4.0 dB. A competitive power consumption of only 5.7 mW is achieved.