| 摘要 |
PURPOSE:To provide the orthogonal degree stablizing circuit for MODEM in multi-channel system which can exactly multiply a base band signal and a carrier frequency signal making the phase different at 90 deg. in the case of performing orthogonal amplitude modulation due to a direct modulation system. CONSTITUTION:A signal at a carrier frequency (f) is outputted from a synthesizer 11 by a frequency setting signal and when the phases of output signals S11 and S12 from a 90 deg. hybrid circuit 2 are not made different at 90 deg. by this output signal, data are read out of a ROM by the frequency setting signal for canceling the phase difference. These data are supplied through a D/A converter to a variable capacitor so as to perform control for changing the capacity of the variable capacitor into capacity to obtain the phase difference at 90 deg., the Ich base band signal and the signal S11 are multiplied by a mixer 3, and the Qch base band signal and the signal S12 can be multiplied by another mixer 4. |
