FOUR-VALUE FSK DEMODULATION CIRCUIT

摘要

PROBLEM TO BE SOLVED: To improve the demodulation accuracy independently of the quantity of a modulation figure by applying binary shaping to in-phase component and an orthogonal component subject to orthogonal detection and conducting FSK demodulation based on a clock signal supplied from a clock generating circuit succeedingly. SOLUTION: A comparator 2 applies binary shaping to an orthogonal detection output outputted from a null IF detection circuit 1. A moving average circuit 4 receiving a binary shaped output calculates a digital moving average based on a timing of a clock signal from a clock generating circuit 3 and stores the average to a table ROM 5. A phase difference circuit 7 receives a phase angleθoutputted from the ROM 5 and a delay phase angleθ' from a delay circuit 6 and obtains the phase difference to provide an output. An integration discharge circuit 10-1 provides an output of an integrated discharge valueΣΔθof phase differencesΔθand an integration discharge circuit 10-2 provides an output of an integrated discharge valueΣ|Δθ|of phase difference absolute values|Δθ|. A discrimination circuit 11 uses a threshold level stored in advance to conduct symbol discrimination of a 4-value FSK.