The US government has ruled all but the smallest TVs will have to be able to receive digital signals by 2007.
The US government wants to phase out analogue TV in December 2006
Manufacturers of TVs, DVDs and video players had tried to block the Federal Communications Commission (FCC) plans, saying it would cost too much money.
But a three-judge panel on the US Court of Appeal said the industry was not making digital tuners available to the public quickly enough.
Congress wants the analogue signal switched over in December 2006.
Circuit judge John G Robinson had ruled that despite the switch-over plan, the FCC had found "a logjam was blocking the development of digital TV".
"Broadcasters are unwilling to provide more DTV [digital television] programming because most viewers do not own DTV equipment," he wrote.
"And the lack of attractive DTV programming makes consumers reluctant to invest in more DTV equipment."
The FCC took on board the ruling because it wanted to make sure that after July 2007 people could buy a television and plug it in without having to buy separate digital receivers or subscribing to a cable service.
'$200 price rise'
"This will ensure that consumers are able to enjoy high-quality digital broadcast programming without the hassle and expense of hooking up a separate set-top box," said FCC chairman Michael Powell.
Champions of the new ruling say digital reception will immediately improve pictures and sound for the 15% of TV viewers who still watch television through a normal aerial.
"Consumers buying TV sets will know that the receivers they buy will continue to receive all broadcast signals, even as broadcasting changes to digital," said Eddie Fritts, the president of the National Association of Broadcasters.
The Consumer Electronics Association, which had fought the ruling, said the new legislation would mean the cost of a television would rise by about $200 (£125).
The first part of the transmission turnover begins next year, when at least half of television 36 inches or larger are required to be digitally compliant.