| 摘要 |
A cancellation circuit is provided for canceling undesirable intermodulation (IM) products in electrical circuitry. The IM cancellation circuit includes a stepping spectrum analyzer which recognizes and measures the frequencies and amplitudes of different signal components of an RF signal across a desired frequency band. This information is forwarded to a processor which contains look-up tables or the like which provides information relating to the frequencies and/or amplitudes of signal components which are intended to reside in the RF signal. By comparison of the look-up tables to the frequencies and amplitudes measured and recognized by the sweeping spectrum analyzer, the processor of the cancellation circuit is able to determine whether the signal components in the RF signal are intended "information" carrying signals or unintended IM products. Where the processor has determined that a signal component is an unintended IM product, the processor controls a variable voltage controlled oscillator and variable amplifier to create a cancellation signal having an identical frequency and amplitude as the frequency and amplitude of the IM product. A phase shifter is provided to shift the phase of the cancellation signal 180 degrees with respect to the IM product and the cancellation signal is combined with the RF signal to produce an output signal having the IM product canceled.
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