摘要 |
A VSB mode detection circuit with a comb filter solves the potential problem of lockout in a situation where an 8 VSB mode signal is being received, with the comb filter being effective, and a change in signal mode suddenly occurs. The arrangement inhibits the first two bytes of the three byte mode information, which two bytes are unspecified for all except the 8 VSB terrestrial mode, and replaces them with zero data. In another embodiment, the 12 symbol delay in the comb filter is bypassed with the complement of the input data for the third byte. When the 8 VSB terrestrial mode has been confidently determined to exist, the inhibition of the first and second bytes (and the inversion of the bypassed third byte) is removed in alternate fields to permit normal comb filter operation. |