Current mirror circuit and analog-digital converter

An analog-digital converter comprising:

• a first constant current source which outputs a constant current to a first node based on a first reference voltage;
• a first MOS transistor which has a source grounded, a gate connected to a second MOS transistor and a drain connected to said first node;
• said second MOS transistor which has a source grounded, a gate connected to said first MOS transistor and a drain connected to a second node;
• a second resistor and a fourth MOS transistor which are connected in series between a power supply voltage and said drain of said second MOS transistor;
• a fifth MOS transistor which is connected in series between said second node and said drain of said second MOS transistor, wherein said second node is connected to a signal voltage through a first resistor;
• a first operational amplifier which has a first input terminal connected to said first node, a second input terminal connected to a third node which is connected to a second reference voltage and an output terminal connected to said gates of said first and second MOS transistors;
• a second operational amplifier which has a first input terminal connected to said third node, a second input terminal connected to said second node and an output terminal connected through a first capacitance to said second node, functioning as an integrator;
• and
• a comparator comparing said output of said second operational amplifier with a predetermined voltage, and outputting said comparison result output.