Antenna checking circuit
An antenna checking circuit includes an antenna-connection-input terminal, a check-request-input terminal, a check-result-output terminal, a switching element having a control end connected to the check-request-input terminal, an input end connected to the antenna-connection-input terminal, and an output end connected to the check-result-output terminal, and a first resistance connected between the check-request-input terminal and the check-result-output terminal. A DC impedance of an antenna between a power supplying point and a ground point is 0Ω, and when a high-level check-request signal is applied to the check-request-input terminal, in a case where the antenna is connected to an antenna-connection terminal, the switching element turns on, and in a case where the antenna is not connected to the antenna-connection terminal, the switching element turns off. Check-result signals that are output to the check-result-output terminal in these cases are different from each other.
1. An antenna checking circuit built into a communication device having an antenna-connection terminal, wherein the communication device is configured to check a connection state of an antenna, the antenna checking circuit comprising:
an antenna-connection-input terminal connected to the antenna-connection terminal;
a check-request-input terminal to which a high-level or low-level check-request signal is input;
a check-result-output terminal to which check results are output;
a switching element having a control end connected to the check-request-input terminal, an input end connected to the antenna-connection-input terminal, and an output end connected to the check-result-output terminal; and
a first resistance connected between the check-request-input terminal and the check-result-output terminal,
wherein the antenna has a ground point, and a DC impedance between a power supplying point and the ground point is 0Ω,
wherein, when the high-level check-request signal is applied to the check-request-input terminal, in a case where the antenna is connected to the antenna-connection terminal, the switching element turns on, and a low-level signal is output to the check-result-output terminal, and in a case where the antenna is not connected to the antenna-connection terminal, the switching element turns off, and a high-level signal is output to the check-result-output terminal,
wherein the switching element is a bipolar transistor having an emitter as the input end and a collector as the output end,
wherein the collector is connected to the check-result-output terminal,
wherein a second resistance having a resistance value smaller than a resistance value of the first resistance is connected between the emitter and the antenna-connection-input terminal, and
wherein a third resistance having a resistance value greater than the resistance value of the second resistance is connected between a base of the transistor and the check-request-input terminal.
2. The antenna checking circuit according to claim 1 , further comprising a communication circuit that includes a high-frequency input/output terminal,
wherein the high-frequency input/output terminal is connected to the antenna-connection terminal 41 via a capacitor.
3. The antenna checking circuit according to claim 1 , wherein the antenna is an inverted F-shaped antenna and includes an antenna conductive portion formed of a metal conductor, a power supplying point, a ground point, and an open end.