Method and apparatus for Class AB audio amplifier output stage voltage protection
First Claim
1. An output circuit for an amplifier, comprising:
- a first power node for coupling to a positive power supply;
a second power node for coupling to a negative power supply,an output node;
first and second PMOS transistors connected in series between the first power node and the output node;
first and second NMOS transistors connected in series between the output node and the second power node;
a first input terminal coupled to a gate of the first PMOS transistor;
a second input terminal coupled to a gate of the first NMOS transistor;
a voltage divider coupled between the output node and a ground node GND, the voltage divider including first and second resistors which are connected at a first node;
a first source follower including a third PMOS transistor, the third PMOS transistor having a gate coupled to the first node and a source coupled to a gate of the second NMOS transistor; and
a second source follower including a third NMOS transistor, the third NMOS transistor having a gate coupled to the first node and a source coupled to a gate of the second PMOS transistor.
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Abstract
An output circuit for a class AB push-pull amplifier includes an upper cascode output stage and a lower cascode output stage. The upper cascode stage includes first and second PMOS transistors connected in series between a positive power supply node and an output node, the first PMOS transistor configured to receive a first complementary input signal. The lower cascode output stage includes first and second NMOS transistors connected in series between a negative power supply node and the output node, the first NMOS transistor configured to receive a second complementary input signal. The output circuit also includes a bias circuit configured for providing a first bias voltage to a gate node of the second NMOS transistor and a second bias voltage to a gate node of the second PMOS transistor, in which the first and the second bias voltages being substantially proportional to the output voltage.
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Citations
20 Claims
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1. An output circuit for an amplifier, comprising:
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a first power node for coupling to a positive power supply; a second power node for coupling to a negative power supply, an output node; first and second PMOS transistors connected in series between the first power node and the output node; first and second NMOS transistors connected in series between the output node and the second power node; a first input terminal coupled to a gate of the first PMOS transistor; a second input terminal coupled to a gate of the first NMOS transistor; a voltage divider coupled between the output node and a ground node GND, the voltage divider including first and second resistors which are connected at a first node; a first source follower including a third PMOS transistor, the third PMOS transistor having a gate coupled to the first node and a source coupled to a gate of the second NMOS transistor; and a second source follower including a third NMOS transistor, the third NMOS transistor having a gate coupled to the first node and a source coupled to a gate of the second PMOS transistor. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. An output circuit for a class AB push-pull amplifier, comprising:
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an upper cascode output stage including first and second PMOS transistors connected in series between a positive power supply node and an output node, the first PMOS transistor configured to receive a first complementary input signal; a lower cascode output stage including first and second NMOS transistors connected in series between a negative power supply node and the output node, the first NMOS transistor configured to receive a second complementary input signal; and a bias circuit, including; a voltage divider coupled to the output node configured for providing a first voltage signal that is related to the voltage at the output node; a first source follower coupled to receive the first voltage signal and configured for providing a first bias voltage to a gate node of the second NMOS transistor in the lower cascode output stage; and a second source follower coupled to receive the first voltage signal and configured for providing a second bias voltage to a gate node of the second PMOS transistor in the upper cascode output stage. - View Dependent Claims (11, 12, 13, 14)
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15. An output circuit for a class AB push-pull amplifier, comprising:
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an upper cascode output stage including first and second PMOS transistors connected in series between a positive power supply node and an output node, the first PMOS transistor configured to receive a first complementary input signal; a lower cascode output stage including first and second NMOS transistors connected in series between a negative power supply node and the output node, the first NMOS transistor configured to receive a second complementary input signal; and a bias circuit configured for providing a first bias voltage to a gate node of the second NMOS transistor and a second bias voltage to a gate node of the second PMOS transistor, the first and the second bias voltages being substantially proportional to the output voltage. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification