Method and circuit for avoiding band interference wave in receiver

• US 20040248531A1
• Filed: 06/24/2004
• Published: 12/09/2004
• Est. Priority Date: 01/12/2001
• Status: Abandoned Application

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Takaki, Tetsuya
• Application Number:
  US10/874,173
• Publication Number:
  US 20040248531A1
• Time in Patent Office: Days
• US Class Current: 455/131
• CPC Class Codes: H03J 5/24 with a number of separate pretuned tuning circuits or separate tuning elements selectively brought into circuit, e.g. for waveband selection or for television channel selection

Abstract

In a method of avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using the oscillation frequency of a local signal oscillator, when the frequency of a reception signal is on the low-frequency side in a reception frequency band, channel setting and route switching control are so performed as to make the reception signal pass through a low-pass filter. A circuit for avoiding a band interference wave is also disclosed.

Claims

1. A method of avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using an oscillation frequency of a local signal oscillator, comprising the steps of setting bandwidths of a plurality of bandpass filters for dividing a band of reception frequencies such that a frequency of a band interference wave produced by the oscillation frequency of the local signal oscillator falls outside a pass band, and switching one of the plurality of bandpass filters to a bandpass filter corresponding to the frequency of the reception signal.

2. A method according to claim 1, wherein the frequency outside the pass band is a frequency obtained by adding a frequency ½

an intermediate frequency to a lowest frequency in each of the bands of the bandpass filters.

3. A circuit for avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using an oscillation frequency of a local signal oscillator, comprising bandpass filters for dividing the band of reception frequencies into a plurality of narrow bands, and a switch for switching said bandpass filters in accordance with a reception frequency of a reception signal corresponding to a set channel, wherein said plurality of bandpass filters respectively have frequency characteristics which set bandwidths such that a frequency of a band interference wave produced by the oscillation frequency of said local signal oscillator falls outside a pass band.

4. A circuit according to claim 3, wherein each of the bandwidths of said plurality of bandpass filters is set such that a frequency obtained by adding a frequency ½

an intermediate frequency to a lowest frequency in each of the bands falls outside the pass band.

5. A circuit for avoiding a band interference wave which is produced in a receiver when a reception frequency used for radio communication is converted into a fixed intermediate frequency by using an oscillation frequency of a local signal oscillator, comprising:

a plurality of bandpass filters which divide a band of reception frequencies into a plurality of narrow bands, and respectively have bandwidths set such that a frequency obtained by adding a frequency ½

the intermediate frequency to a lowest reception frequency in each band falls outside a pass band;

a switch for switching said bandpass filters in accordance with a reception frequency; and

a local signal oscillator for generating a fixed intermediate frequency by changing a generated oscillation frequency in accordance with a reception frequency.