Method for determining whether there is digital signal in digital TV set

The method carries out following flow: if signal received from each channel, the method determines PWL (Power Level) of kernel point setup in advance at specific location of the said each received signal, and determines whether the PWL value is within critical range; if yes, then determining whether deviation of PWL value is within critical range setup in advance; if yes, then the said input signal is determined as digital signal. The method ensures that decoding function is operated only for meaningful digital signal so as to guarantee stability and service time of chip.