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发现了一种数字式差分角度解调器,适用于通过电话线路的高比特速率数据传输系统,电话线路是话音等级的,是可以任意选择的。解调器从相移中频调制信号中再生出时钟信号。时钟信号用作同步地选通一高频计数器输出,使其进入检波器电路,检波器精确地抽样取出包含待定相移信息的中频信号的那一部份。高速计数器对中频载波锁相,所以矩形中频信号的零交叉点将出现在二进计数器输出相位为22.5°的奇数倍时。检波器电路中的两个独立的寄存器接收相继的计数器最有效的比特输出值,这一输出取决于从含有信息的那一信号精确部份的相位抽样。一个并行的加法器确定相继的计数间的差别,加法器的每次计数表征了在此间隔内原来接收的信息的相位改变。高速计数器的相位锁定保证了由系统噪声引起相位随机变化,而将不会叠加地影响检测运算。编码器将并行加法器输出的相移信号恢复成多电平数据信号。
A digital differential angle demodulator was found for a high bit rate data transmission system over a telephone line that is voice-grade and is arbitrarily chosen. The demodulator reproduces the clock signal from the phase-shifted IF modulated signal. The clock signal is used for synchronously gating the output of a high frequency counter into the detector circuit which samples the exact portion of the intermediate frequency signal containing the pending phase shift information by sampling. The high-speed counter locks the IF carrier, so the zero-crossings of the rectangular IF signal appear at an odd multiple of 22.5 ° of the binary counter output phase. Two separate registers in the detector circuit receive the most significant bit output value from successive counters, depending on the phase sample from the exact portion of the signal containing the information. A parallel adder determines the difference between successive counts, each count of the adder characterizes the phase change of the information originally received during this interval. The phase lock of the high-speed counter ensures that the phase changes randomly due to the system noise and will not affect the detection operation in a superimposed manner. The encoder returns the phase-shifted signal output by the parallel adder to a multi-level data signal.