INDIRECT MODULATION CIRCUIT AND RADIO EQUIPMENT USING THE CIRCUIT

摘要

PROBLEM TO BE SOLVED: To eliminate an image component generated in a mixer output of an indirect modulation circuit with a high pass filter circuit. SOLUTION: In this indirect modulation circuit, a frequency generator 10 generates a local oscillation signal of a frequency being 4/5 times as long as a transmission frequency. A modulator 12 modulates a signal of a frequency being 2/5 times as long as the transmission frequency with a baseband signal. A modulator 14 generates a signal of a frequency being 3/5 times as long as the transmission frequency. A mixer 15 mixes a modulation signal of a frequency being 2/5 times as long as the transmission frequency with the signal of a frequency being 3/5 times as long as the transmission frequency to generate a signal of the transmission frequency. An image component generated in an output of the mixer 15 becomes a frequency component being 1/5 times as long as the transmission frequency. Since the frequency of the image component is separated for a frequency component being 4/5 times as long as the transmission frequency in comparison with the transmission frequency, the image component can be eliminated by a high pass filter circuit whose circuit scale is small.