Patent ID: 8059757

Claim:
A signal processing device comprising: a signal generator for generating a test signal including a positive signal having a first amplitude in a direction where the voltage is higher than a preset reference voltage and a negative signal having a second amplitude that is the same as said first amplitude in a direction where the voltage is lower than said reference voltage; a signal processing circuit for implementing frequency conversion of said test signal or a modulated signal supplied from said signal generator; a level detecting part for detecting a signal outputted from said signal processing circuit and outputting a detected signal including a detected positive signal corresponding to said positive signal and a detected negative signal corresponding to said negative signal; a level comparator for comparing the level of said detected positive signal and the level of said detected negative signal to output the comparison result indicating which level of said detected positive signal and said detected negative signal is higher; and an offset adjuster for generating an offset correction signal for making a level difference between said detected positive signal and said detected negative signal within a preset permissible range by shifting the reference voltage, based on the comparison result of said level comparator, wherein said signal generator makes the offset correction of the modulated signal in accordance with said offset correction signal supplied from said offset adjuster.