DEVICE FOR JUDGING DIGITAL/ANALOG SIGNAL, RECEIVER AND METHOD FOR JUDGING DIGITAL/ANALOG SIGNAL

摘要

PROBLEM TO BE SOLVED: To make a decision whether a received signal is an analog signal or a digital signal without demodulating the signal. SOLUTION: A band-pass filter 26 provided in a signal judging section 2 has such band characteristics as passing the video carrier of an analog signal and the modulated wave of a digital signal and a band-pass filter 28 has intermediate band characteristics of video carrier and audio carrier. A first intermediate frequency signal outputted from a mixer 14 is subjected to level adjustment through an amplifier 25 before being fed to the band-pass filters 26 and 28. A comparison circuit 30 compares the output level difference between two signals detected by detection circuits 27 and 29 with a specified threshold level. A decision is made that a received TV signal is an analog signal if the output level difference exceeds the threshold level otherwise it is a digital signal.