Patent ID: 8107009

Claim:
A television-connection-state detecting device comprising: a resistor element that is connected to a television connection terminal that outputs an analog video signal that is to be displayed on a television receiver, the resistor element having the same resistance value as that of a termination resistor of a connection terminal of the television receiver that can be connected to the television connection terminal; a reference voltage generation circuit that generates reference voltages for comparing a voltage signal level at the television-connection-terminal-side end of the resistor element and a voltage signal level at the opposite-side end of the resistor element, the reference voltage generation circuit generating each of the reference voltages in such a manner that a first reference voltage for the television-connection-terminal-side end of the resistor element is higher than a second reference voltage for the opposite-side end of the resistor element by a predetermined level difference; a first clamping circuit that clamps a voltage signal level at the television-connection-terminal-side end of the resistor element at the first reference voltage; a second clamping circuit that clamps a voltage signal level at the opposite-side end of the resistor element at the second reference voltage; a comparison circuit that has a first input terminal into which a voltage signal that has been subjected to clamping processing performed by the first clamping circuit is inputted and further has a second input terminal into which a voltage signal that has been subjected to clamping processing performed by the second clamping circuit is inputted, the comparison circuit outputting a voltage signal that has a level corresponding to high/low relationship between a voltage signal level at the first input terminal and a voltage signal level at the second input terminal that is found as a result of a comparison made therebetween; a first low-pass filter that is provided between the first input terminal of the comparison circuit and the first clamping circuit; a second low-pass filter that is provided between the second input terminal of the comparison circuit and the second clamping circuit; and a judging section that makes a judgment as to whether an analog video signal input device is connected to the television connection terminal or not on the basis of a voltage signal level outputted from the comparison circuit.