Patent ID: 7139534

Claim:
A transmission circuit comprising: modulated signal generating means for generating a modulated signal including a phase component and an amplitude component; a modulated signal line for transmitting the modulated signal, the modulated signal line being connected to the modulated signal generating means; modulated signal detecting means for detecting at least the amplitude component of the modulated signal generated by the modulated signal generating means, the modulated signal detecting means being connected to the modulated signal line; an amplitude component line for transmitting the amplitude component of the modulated signal, the amplitude component line being connected to the modulated signal detecting means; threshold value inputting means for inputting a threshold value for switching a method for modulating the modulated signal; and judging means for judging whether or not an amplitude value of the amplitude component of the modulated signal is larger than the threshold value input from the threshold value inputting means, the judging means being connected to the amplitude component line, wherein the modulated signal detecting means also detects the phase component of the modulated signal, and the transmission circuit further comprises: a phase component line for transmitting the phase component of the modulated signal, the phase component line being connected to the modulated signal detecting means; a constant-voltage supply line for supplying a constant voltage; first selection outputting means for outputting the modulated signal if the amplitude value of the amplitude component is smaller than or equal to the threshold value, while outputting the phase component if the amplitude value of the amplitude component is larger than the threshold value, based on a judgment result of the judging means, the first selection outputting means being connected to the modulated signal line and the phase component line; and second selection outputting means for outputting the constant voltage if the amplitude value of the amplitude component is smaller than or equal to the threshold value, while outputting the amplitude component if the amplitude value of the amplitude component is larger than the threshold value, based on the judgment result of the judging means, the second selection outputting means being connected to the amplitude component line and the constant-voltage supply line.