Patent ID: 8593222

Claim:
An amplifier, comprising: an output stage circuit electrically coupled to a supply voltage and a ground voltage; a current source having a node to provide a current; a PMOS input pair coupled to the node and the ground voltage, and controlled by an input voltage; an NMOS input pair coupled to the supply voltage and controlled by the input voltage; and a current transferring circuit coupled to the node and the NMOS input pair; wherein when the input voltage is less than a specific value, the PMOS input pair is turned on, and the NMOS input pair and the current transferring circuit are turned off, so that the current flows into the PMOS input pair through the node; and when the input voltage is larger than or equal to the specific value, the PMOS input pair is turned off, and the NMOS input pair and the current transferring circuit are turned on, so that the current flows into the NMOS input pair through the node and the current transferring circuit; wherein the current transferring circuit includes: a first NMOS transistor having a first terminal coupled to the NMOS input pair, and a second terminal coupled to the ground voltage, a second NMOS transistor having a first terminal coupled to a control terminal of the first NMOS transistor, a second terminal coupled to the ground voltage, and a control terminal coupled to the control terminal of the first NMOS transistor, and a first PMOS transistor having a first terminal coupled to the node, a second terminal coupled to the first terminal of the second NMOS transistor, and a control terminal for receiving a control voltage; and wherein the specific value is the sum of the control voltage and the threshold voltage of the first PMOS transistor minus a voltage difference between the input voltage and the node.