Differential input circuit capable of broadening operation range of input common mode potential

A differential input circuit, comprising

• a first differential pair including first and second transistors having the same conductivity type and formed of a semiconductor of one of a first conductivity type in which a conduction electron density is larger than a hole density and a second conductivity type in which the hole density is larger than the conduction electron density, for receiving a differential input signal, and for transmitting a differential output signal;
• a second differential pair including third and fourth transistors constructed from a semiconductor of the same conductivity type as said first and second transistors constituting said first differential pair, and which is commonly connected to an output of said first differential pair;
• input means for supplying a differential signal to said first differential pair;
• output means for adding differential signals respectively supplied from said first and second differential pairs so as to output an added differential signal;
• and
• a differential amplifier circuit at least comprising a third differential pair including fifth and sixth transistors which are formed by a semiconductor of the second conductivity type different from said first conductivity type forming said first through fourth transistors constituting said first and second differential pair and having a common bias current source;
• for inputting said differential input signal commonly with the first differential pair;
• and for generating a differential amplified signal which is supplied to said second differential pair;
• so that a potential of an output operating point is set to operate said third and fourth transistors of said second differential pair;
• wherein, when a common mode input range of said differential input signal is outside a circuit operating range of said differential amplifier circuit, an output potential of said differential amplifier circuit causes said second differential pair to stop operating.