| 摘要 |
PURPOSE:To facilitate the temperature compensation of an input signal D/A converter by using a temperature compensation D/A converter having the same electric characteristic as an input signal D/A converter. CONSTITUTION:Inputted digital signals 1, 2 are converted into 4-value analog signal including temperature fluctuation by input signal D/A converters 1, 7 respectively and given to a terminal (a) of double balanced modulators 3, 6 and an output of a temperature compensation D/A converter 11 is given respectively to a terminal (b) of modulators 3, 6 via a variable attenuator 12 giving an attenuation to the insertion loss of a low pass filter. Then the an IF signal corresponding to the 4-value analog signal whose temperature fluctuation is compensated in the A/D converter 1 is extracted and synthesized by a hybrid circuit 5, and a 16-value QAM wave arranged in correct location is sent. |
