Operational amplifying circuit and liquid crystal panel drive device using the same

An operational amplifier circuit comprising:

• first and second P-type transistors of a P-t e differential pair;
• first constant current source connected between sources of said first and second P-type transistors which are connected in common, and a positive side power supply voltage;
• a series connection of a first capacitor and a first switch which is in parallel to said first constant current source;
• first and second N-type transistors of an N-type differential pair, wherein gates of said first P-type transistor and said first N-type transistor are connected with an inversion input node, and gates of said second P-type transistor and said second N-type transistor are connected with a non-inversion input node;
• a second constant current source connected between sources of said first and second N-type transistors which are connected in common, and a negative side power supply voltage;
• a series connection of a second switch and a second capacitor connected in parallel to said second constant current source;
• a cascade connection type first current mirror circuit configured to convert output current signals from said N-type differential pair into a voltage signal;
• a cascade connection type second current mirror circuit configured to convert output current signals from said P-type differential pair into a voltage signal;
• third and fourth constant current sources connected between said first current mirror circuit and said second current mirror circuit and configured to supply currents as floating current sources;
• an output N-type transistor and an output P-type transistor connected in series between said positive side power supply voltage and said negative side power supply voltage;
• a first phase compensation capacitor provided between an output node between said output N-type transistor and said output P-type transistor and said first current mirror circuit, and a second phase compensation capacitor provided between said output node and said second current mirror circuit.

A liquid crystal driver circuit comprising:

• a buffer circuit in which an operational amplifier circuit is connected as a voltage follower;
• and
• a gray-scale voltage generating circuit configured to generate a gray-scale voltage based on an input signal to output to said buffer circuit,
• wherein said operational amplifier circuit comprises:
• a first differential amplifier section comprising a P-type differential pair of P-type transistors;
• a second differential amplifier section comprising an N-type differential pair of N-type transistors;
• intermediate stage connected with outputs of said first and second differential amplifier sections and comprising a first current mirror circuit of P-type transistors, and a second current mirror circuit of N-type transistors;
• and
• an output stage configured to amplify a power of an output of said intermediate stage,
• wherein said first differential amplifier section comprises a first current source and a first capacitor between sources of said P-type transistors of said P-type differential pair and a positive side power supply voltage, and
• wherein said second differential amplifier section comprises a second current source and a second capacitor between sources of said N-type transistors of said N-type differential pair and a negative side power supply voltage.

A liquid crystal display comprising:

• an operational amplifier circuit comprising first and second switches;
• and
• a control circuit configured to generate first and second control signals used to control said first and second switches to supply to said operational amplifier circuit,
• wherein said operational amplifier circuit comprises:
• a first differential amplifier section comprising a P-type differential pair of P-type transistors;
• a second differential amplifier section comprising an N-type differential pair of N-type transistors;
• an intermediate stage connected with outputs of said first and second differential amplifier sections and comprising a first current mirror circuit of P-type transistors, and a second current mirror circuit of N-type transistors;
• and
• an output stage configured to amplify a power of an output of said intermediate stage,
• wherein said first differential amplifier section comprises a first current source and a first capacitor between sources of said P-type transistors of said P-type differential pair and a positive side power supply voltage,
• wherein said second differential amplifier section comprises a second current source and a second capacitor between sources of said N-type transistors of said N-type differential pair and a negative side power supply voltage,
• wherein said first switch is provided between the sources of said P-type transistors of said P-type differential pair and said first capacitor, and said second switch is provided between the sources of said N-type transistors of said N-type differential pair and said second capacitor, and
• wherein said first switch and said second switch are alternately opened or closed in synchronization with an input differential signal supplied to said first differential amplifier and said second differential amplifier.