Digital Phase Demodulator

Injection-locked oscillators can perform a wide variety of functions required in microwave radio relays, such as amplification, amplitude limitation, 1 frequency modulation 2 and demodulation 3 to mention only the most important applications. It is shown in this paper that injection-locked oscillators can also be used as narrow band tunable filters for angle modulated signals. These filtering properties can be used in a digital demodulator for coherent phase detection and such a demodulator is described here. Its configuration, shown in Fig. 1, is similar to the injectionlocked oscillator FM receiver proposed by C. L. Ruthroff. 3 The principles of operation, however, are different. For proper operation of the injection-locked oscillator FM receiver the output signal of the oscillator contains all of the frequency modulation on the input signal. This signal is multiplied by a fraction of the input signal to 933 934 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH I SIN[wt+ 0(t)] 1971 Fig. 1--Scheme of the digital demodulator for coherent phase detection.