Envelope detection of PN sequences accompanying VSB signal to control operation of QAM/VSB DTV receiver

A television signal radio receiver for selectively receiving vestigial-sideband (VSB) digital television (DTV) signals and television signals of at least one other type, each said VSB DTV signal having pseudo-random noise (PN) sequence information in the initial data segment of each successive one of the data fields thereof, said television signal radio receiver comprising:

• a tuner for supplying analog intermediate-frequency carrier modulated in accordance with a selected one of said television signals, said modulated analog intermediate-frequency carrier having an envelope exhibiting amplitude variations in response to said pseudo random sequences and to said symbol codes;
• an envelope detector for detecting the amplitude of said envelope amplitude variations to supply an envelope detector response;
• a PN sequence presence detector responsive to said envelope detector response for detecting the occurrence of said PN sequence information therein when a VSB DTV signal is being received, said PN sequence presence detector providing an output signal with an indication of each such occurrence which indication is sustained for a period of time at least as long as the duration of a data field;
• and
• circuitry, for operating the television signal radio receiver in a VSB DTV reception mode responsive to said PN sequence presence detector providing an output signal with an indication of the occurrence of said PN sequence information in said baseband signal, and for operating the television signal radio receiver in a reception mode for another type of television signal responsive to said PN sequence presence detector providing an output signal without indication of the occurrence of said PN sequence information in said baseband signal.