HDMI and VGA compatible interface circuit

A signal transmitting circuit, comprising:

• a HDMI signal transmitting unit adapted to output a HDMI signal;
• a VGA signal transmitting unit adapted to output a VGA signal;
• a VGA signal processing unit connected to the VGA signal transmitting unit, the VGA signal processing unit adapted to receive the VGA signal from the VGA signal transmitting unit, and combine a detection signal to the VGA signal to form a combination signal;
• and
• a transmitting control unit connected to the VGA signal processing unit and the HDMI signal transmitting unit, the transmitting control unit adapted to receive the combination signal and the HDMI signal, distinguish the combination signal and the HDMI signal, and respectively output the VGA signal extracted from the joint signal and the HDMI signal to corresponding receivers;
• a port, wherein the transmitting control unit is connected to the VGA signal processing unit and the HDMI signal transmitting unit via the port, and the port is adapted to receive the combination signal from the VGA signal processing unit or receive the HDMI signal;
• the transmitting control unit comprises a signal channel switch circuit, the signal channel switch circuit comprises an input end, a first output end, and a second output end, the input end is connected to the port, and the first output end is adapted to connected to a VGA signal receiver, and the second output end is adapted to connected to a HDMI receiver;
• the transmitting control unit comprises a control circuit, the signal channel switch circuit comprises a control end, the control circuit connected to the control end, the control circuit is adapted to link the input end to the first output end or the second output end;
• the control circuit comprises an on-off, the on-off comprises a control pin, a first linking pin, and a second linking pin, the first linking pin is connected to the control end, the second linking pin is connected to ground, the control pin is connected to the port, the control pin is adapted to detect a type of a signal received by the port, and the control pin is adapted to turn on or turn off the on-off according to a type of a signal received by the port;
• wherein the port comprises a detection pin, the detection pin is connected to the control pin, the detection pin is adapted to receive a low level voltage ground signal when the port receives the HDMI signal, the detection signal is a high level voltage signal, and the detection pin is adapted to receive the detection signal when the port receives the combination signal.