| 摘要 |
PURPOSE:To demodulate a QPSK modulation wave accurately and stably by employing a 2fc VCO, a 1/2 frequency divider and a -pi/2 phase shifter for the demodulator. CONSTITUTION:A QPSK modulation wave (carrier frequency is fc) is inputted to the demodulator, in which the wave is processed by a BPF 12 and an AGC amplifier 14. A multiplier 16a multiplies the processed QPSK modulation wave with a 1st carrier being an output of a 1/2 frequency divider 8 to obtain an in-phase detection output I. A multiplier 16b multiplies the processed QPSK modulation wave with a 2nd carrier being an output of a -pi/2 phase shifter 20 to obtain a 90 deg. phase detection output Q. The output of the multiplier 16a is inputted to multipliers 26a, 30b via an LPF and a limiter. The output of the multiplier 16b is inputted to multipliers 26b, 30a, via an LPF and a limiter. The phase difference between the detected outputs I, Q is detected by the multipliers 30a, 30b and an adder 32 to control a VCO 22 via an LPF 34. On the other hand, the output of the multipliers 26a, 26b is given to an AGC amplifier 14 via an adder 36 and an LPF 40 to control the gain. |
