Patent ID: 7116950

Claim:
A direct-conversion transmitting circuit, characterized by a local modulation circuit comprising first and second mixers, and first and second low-pass filters, first and second gain/bias adjustment means, and a first phase shifter, wherein high frequency output terminals of said first and second mixers are connected to each other; an output terminal of said first low-pass filter is connected to an input terminal of said first mixer; the input terminal of said first low-pass filter is directly connected to an output terminal of said first gain/bias adjustment means; the output terminal of the second low-pass filter is connected to an input terminal of the second mixer; the input terminal of the second low-pass filter is directly connected to an output terminal of said second gain/bias adjustment means; a first output terminal of said first phase shifter is connected to a local signal input terminal of said first mixer; a second output terminal of said first phase shifter is connected to a local signal input terminal of said second mixer; and input signals are applied to an input terminal of said first gain/bias adjustment means and an input terminal of said second gain/bias adjustment means, respectively, wherein each circuit of said first and second low-pass filters is composed of a filter whose order is at least a second order, and wherein said first and second low-pass filter circuits are each composed of a Sallen-Key type filter circuit, the Sallen-Key type filter is composed of first and second resistors, first and second capacitors, and a first transistor, and a first terminal of said first resistor is an input of the filter; a second terminal of said first resistor is connected to a first terminal of said second resistor; a second terminal of said second resistor is connected to a base of the first transistor; a first terminal of said first capacitor is connected to the second terminal of said first resistor; a second terminal of said first capacitor is connected to an emitter of said first transistor; a first terminal of said second capacitor is connected to the second terminal of said second resistor; a second terminal of said second capacitor is connected to a grounding potential; a collector of said first transistor is connected to a power source potential; and an emitter of said first transistor is an output terminal of the filter.