Output current detecting circuit and transmission circuit

A transmission circuit, comprising:

• an output circuit including a first output transistor and a second output transistor connected between a power source voltage terminal and a constant potential point in a serial mode;
• a gate control circuit for generating a pair of AMI-coded control signals to be supplied to control terminals of the first output transistor and the second output transistor, respectively;
• a current detecting transistor having a size smaller than sizes of the output transistors, and a control terminal, to which a voltage is applied that is the same as voltages applied to the control terminals of the output transistors, to flow a current according to the size of the current detecting transistor through the current detecting transistor;
• a first resistance element connected to the current detecting transistor in a serial mode;
• a comparison circuit for comparing a voltage converted by the first resistance element and a predetermined reference voltage to judge a magnitude of a current flowing through the output transistors;
• and
• a reference voltage generating circuit for generating the reference voltage,
• wherein:
• the reference voltage generating circuit includes a constant current circuit flowing a constant current and a second resistance element having one terminal connected to the power source voltage terminal, the reference voltage generating circuit generating the reference voltage based on a power source voltage to be applied to the power source voltage terminal by converting the constant current generated by the constant current circuit into a voltage by flowing the constant current through the second resistance element;
• an output of the comparison circuit is supplied to the gate control circuit, which generates control signals for turning off both the first output transistor and the second output transistor when the current flowing through the output transistors exceeds a predetermined current value;
• and
• the transmission circuit further comprises a first MOS transistor connected between the constant current circuit and the second resistance element, the first MOS transistor having a gate terminal to which a voltage is applied that is the same as the voltage applied to the control terminal of the current detecting transistor.