Operational amplifier stages

An operational amplifier comprising:

• two voltage signal inputs and an output;
• a positive and a negative supply rail;
• an input stage including a differential buffer amplifier, and a transconductance section connected to the differential buffer amplifier;
• the differential buffer amplifier including means for producing a differential voltage signal representative of the voltage difference between voltage signal inputs, and the transconductance section including means for converting the differential voltage signal to an input stage output current;
• a gain stage including a gain stage input and a gain stage output;
• a first current gain element;
• a voltage controlled second current gain element;
• current controlled first and second voltage sources;
• an integrating capacitor;
• the gain stage input being connected to the first current gain element, an end of the integrating capacitor, and an input of the first voltage source;
• another end of the integrating capacitor being connected to an input of the second voltage source;
• an input to the second current gain element being connected to an output of the first current gain element;
• an output of each of the first and second voltage sources is connected to the second supply rail;
• a first and a second voltage control input of the second current gain element connected one to each of another voltage output of each of the first and second voltage sources;
• an output of the second gain element is connected to the gain stage output;
• an output stage including an output stage input and an output stage output, a current driving amplifier, first and second current mirrors, the first current mirror being connected to the first supply rail and the second current mirror being connected to the second supply rail, and a first and a second common emitter output transistor, the output transistors being connected between the first and second supply rails and connected to the stage output wherein, the driving amplifier supplies current to the first current, mirror and one of the output transistors, the first current mirror supplies current to the second current mirror, a second current mirror and the current source supply current to the other output transistor and the output transistors supply current to the output stage output;
• a feedback resistor;
• the input stage output being connected to the gain stage input;
• the gain stage output being connected to the output stage input;
• and the output stage output being connected to the output;
• the feedback resistor being connected to the other output of the second voltage source of the gain stage;
• whereby the input stage is operable within a range of common mode voltage signals at the voltage signal inputs or the range including common mode voltage signals at, the range beyond the second supply rail;
• and whereby an input current signal at the gain stage input from the input stage output is integrated by the capacitor the integrated current being removed from the input current signal producing a modified input current signal, the modified current signal is amplified by the first and second gain elements to produce an output current at the gain stage output, the gain of the second element being controlled by a different voltage between the two voltage sources the first voltage source controlled by the modified current signal while the second voltage source is controlled by the integrated current;
• and whereby one alternate portion of the alternating signal at the output stage input from the gain stage output directly drives one of the output transistors, and the other alternate portion drives the first and consequently the second current mirror, the current in the second current mirror being compared against the reference current source current to drive the other output transistor;
• and whereby the gain of the second current gain element of the gain stage is reduced by the voltage across the feedback resistor.