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Dual-conversion-transmitter

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Dual conversion transmitter

Details

Inventors: Ohmagari, Shinichi; Yamamoto, Osamu;
Assignee: NEC Corporation (Tokyo, JP)
Primary Examiner: Eisenzopf; Reinhard J.
Assistant Examiner: Pham; Chi H.
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb & Soffen

A transmitter using a dual conversion system which effects frequency conversion twice has a local oscillator (113) for generating a first local oscillation signal, a multiplier (118) for multiplying the frequency of the first local oscillation signal to produce a second local oscillation signal, a first mixer (115) for mixing the first local oscillation signal and first IF signal to produce a second IF signal, and a second mixer (120) for mixing the second local oscillation signal and second IF signal to produce a signal to be transmitted. A voltage controlled filter (116) whose center frequency varies with the frequency of the first local oscillation signal is connected to the output of the first mixer (115).

DETAILED DESCRIPTION It is therefore an object of the present invention to provide an inexpensive transmitter.
It is another object of the present invention to provide a transmitter implemented with a filter which does not have a sharp cut-off characteristic at the outside of the band.
According to the invention, a transmitter has a voltage controlled filter connected to the output of a mixer which mixes a modulated signal or first IF signal and a local oscillation signal to produce a second IF signal.
The center frequency of the voltage controlled filter is varied in matching relation to the frequency of the local oscillation signal.
The transmitter removes unnecessary components close to the frequency of the second IF signal by means of a variable frequency band pass filter which does not need to have a sharp cut-off characteristic at the outside of the band.

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