High-frequency receiver and portable device using the same

A portable device comprising:

• a high-frequency receiver including:
• (a) a high-frequency signal input terminal for receiving high-frequency signals;
• (b) a tuned filter coupled to the input terminal;
• (c) a first mixer including a double balance mixer circuit having a first input terminal which receives an output signal from the tuned filter and a second input terminal which receives an output signal from a local oscillator;
• (d) an output terminal for receiving an output signal from the first mixer;
• (e) a second mixer connected between the tuned filter and the output terminal, and having an image rejection mixer circuit which receives an output from the local oscillator;
• (f) a power supply control circuit coupled to the image rejection mixer circuit and controlling a power supply which powers the image rejection mixer circuit;
• (g) an image interference determiner coupled to an input side of the power supply control circuit;
• and
• (h) a phase locked loop (PLL) circuit coupled to the local oscillator,
• wherein the image interference determiner determines whether or not image interference exists at a present position with respect to a channel desirable to be received, and the power supply control circuit stops the supply of power to the first mixer so as to allow the first mixer to work as the double balance mixer when the determiner determines no image interference exists,
• a position data obtaining means coupled to an antenna and obtaining data of a present position;
• a signal processor for receiving an output from the high-frequency receiver;
• and
• a display and an audio output device to which an output signal is supplied from the signal processor,
• wherein the image interference determiner receives an output signal from the position data obtaining means at its first input terminal, and connects to a memory at its second input terminal, and the memory stores a plurality of receivable frequencies corresponding to the position data,
• wherein the image interference determiner determines, in response to the position data obtained from the position data obtaining means, whether or not a received channel involves image interference, and when the determiner determines no image interference happens in the received channel, the determiner turns off an image rejection mixer circuits of the mixer, and switches the mixer to a double balance mixer circuit.