Patent ID: 8199253

Claim:
A clock range setting device, setting N lead clock ranges corresponding to N video signals according to N framing codes and N horizontal synchronizing pulses, wherein N is a positive integer, the clock range setting device comprising: a horizontal counter configured to count a horizontal counter value and reset the horizontal counter value when the horizontal counter receives one of the horizontal synchronizing pulses; a filter unit generating a plurality of clock intermediate values, the filter unit obtaining a lead clock of the i th teletext video signal according to the i th lead clock range, and the filter unit averaging the lead clocks of the 1 st to the i th teletext video signals to generate the i th clock intermediate value when the filter unit detects the i th framing code, wherein i is an integer, and 1≦i≦N; a clock detecting unit detecting a level change of the lead clock of the (i+1) th teletext video signal according to the i th clock intermediate value, thereby generating a current clock cycle number corresponding to the lead clock of the (i+1) th teletext video signal, and the clock detecting unit further generating the current clock cycle number corresponding to the lead clock of the 1 st teletext video signal according to a predetermined intermediate value; a first infinite impulse response filter (IIR filter) generating a plurality of number mean values, and the first IIR filter averaging the current clock cycle numbers of the lead clocks of the 1 st to the i th teletext video signals to generate the i th number mean value when the first IIR filter detects the i th framing code; and a clock range modulator configured to set an end position of the (i+1) th lead clock range according to the current clock cycle number of the lead clock of the (i+1) th teletext video signal and the i th number mean value, and the clock range modulator configured to set an initial position of the (i+1) th lead clock range when the horizontal counter value reaches to a range initial value, wherein the clock range modulator further feeds the (i+1) th lead clock range back to the filter unit.