| 摘要 |
The invention relates to a suppression circuit which allows at least one selected frequency to be excised from the output signal of an amplifier, such as an RF power amplifier 54. The circuit down-converts a feedback signal 52a derived from the amplifier output into baseband signals, which may be quadrature signals produced by mixers 58a&b. Each of the quadrature baseband signals may be inverted 64a&b and filtered 66a&b to remove signals falling outside the excision frequency band. The filtered quadrature signals are subsequently up-converted into an RF signal by mixers 70a&b, combined 72, and fed back to the input of the power amplifier via a coupler 74. Mixers 58a&b and 70a&b may receive a local oscillator signal from an oscillator 62 which operates at the excision frequency at which it is desired to suppress (fig.4: notch) a signal such as an intermodulation product from the output of the power amplifier. Multiple feedback loops may be provided (fig.3) to suppress multiple spurious signals. The invention overcomes a limitation of conventional Cartesian loops, which are not practical for wideband signals. |
