Interface circuit

Abstract

An interface circuit according to one aspect of the present invention may include a receiving circuit operating on a supply voltage lower than a high-level voltage value of an input binary signal, an input level determination circuit generating an input level determination signal having a frequency higher than a frequency of the binary signal and controls whether to output the input level determination signal or not, based on a voltage level of the binary signal, and an AC coupling element connected between an output terminal of the input level determination circuit and an input terminal of the receiving circuit.

What is claimed is: 
     
         1 . A board comprising:
 a connector terminal;   an oscillating circuit;   an output control circuit coupled to the connector terminal, the oscillating circuit, a ground node and a power supply node, wherein the output control circuit is supplied with a voltage having only one voltage value higher than a ground voltage supplied from the ground node;   an AC coupling element coupled to the output control circuit; and   a receiving circuit coupled to the AC coupling element   
     
     
         2 . The board according to  claim 1 , wherein the receiving circuit receives a voltage signal having a higher voltage value than the ground voltage. 
     
     
         3 . The board according to  claim 1 , wherein an input of an AC signal toward the receiving circuit is stopped based on a signal inputted into the connector terminal. 
     
     
         4 . The board according to  claim 1 , wherein the receiving circuit includes an input node coupled to the AC coupling element and another power supply node, and comprises a clamp circuit coupled to both the input node and the another power supply node. 
     
     
         5 . A board comprising:
 a connector terminal;   an oscillating circuit;   an output control circuit coupled to the connector terminal, and the oscillating circuit to output an AC signal;   an AC coupling element coupled to the output control circuit; and   a receiving circuit coupled to the AC coupling element, wherein an input of the AC signal toward the receiving circuit is stopped based on a signal inputted   into the connector terminal.   
     
     
         6 . The board according to  claim 5 , wherein the output control circuit stops outputting the AC signal based on the signal inputted into the connector terminal. 
     
     
         7 . A board comprising:
 a connector terminal;   an oscillating circuit;   an output control circuit coupled to the connector terminal, the oscillating circuit, a ground node and a power supply node, an AC coupling element coupled to the output control circuit; and   a receiving circuit coupled to the AC coupling element, wherein the receiving circuit receives a voltage signal having a higher voltage value than a ground voltage supplied from the ground node.