Analog amplifier for recovering abnormal operation of common mode feedback

An operational amplifier comprising:

• a first stage and a second stage of the operational amplifier;
• and
• a current source disposed between the first stage and the second stage, so as to increase a voltage of a node while a first input transistor of the first stage is turned off and to prevent a voltage of an input transistor of the operational amplifier from dropping down to a threshold or less,
• wherein the current source is configured to provide a predetermined current between a drain terminal of an output transistor of the first stage and a gate terminal of a transistor of the second stage, and
• wherein, if an input bias voltage of a first output transistor of the first stage increases, an output voltage of a third transistor of the second stage reduces and an output voltage of the first output transistor of the first stage increases, so that an operation point of an output voltage increases at an output terminal.

An analog variable amplifier comprising:

• a input resistor;
• a feedback resistor;
• and
• a differential amplifier comprising:
• a first input terminal,
• a second input terminal,
• a first input transistor,
• a second input transistor,
• a first output transistor,
• a second output transistor,
• a first current source,
• a second current source,
• a first output terminal, and
• a second output terminal,
• wherein the first current source is configured to provide a predetermined current to a first node between a drain of the first input transistor and a drain of the first output transistor, so as to increase a voltage of the first node while the first transistor is turned off,
• wherein the second current source is configured to provide a predetermined current to a second node between a drain of the second input transistor and a drain of the second output transistor, so as to increase a voltage of the second node while the second input transistor is turned off,
• wherein, if the input resistor is greater than the feedback resistor by a predetermined ratio, the first input transistor is off, and
• wherein the first input transistor and the first output transistor are arranged so that the voltage of the first node decreases and an operation point of an output voltage at the first output terminal increases if an input bias voltage of the first output transistor increases or decreases, while the first transistor is off.