Method and Apparatus for Class AB Audio Amplifier Output Stage Voltage Protection
a technology for audio amplifiers and output stages, applied in amplifiers, amplifiers with semiconductor devices/discharge tubes, amplifiers, etc., can solve the problems of complex process, high cost, and limited use of conventional cascode amplifiers, so as to achieve higher breakdown voltage, more complicated process, and the effect of high cos
Active Publication Date: 2016-01-14
NUVOTON
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AI Technical Summary
Benefits of technology
This approach allows cascode transistors to handle large signals without exceeding their breakdown voltages, reducing the need for costly high-breakdown voltage devices and improving operational efficiency.
Problems solved by technology
The inventor has observed that conventional cascode amplifiers suffer from various limitations.
However, this configuration can only handle large signals if the devices have a higher breakdown voltage than half the maximum voltage swing.
This is undesirable because devices with higher breakdown voltages often require more complicated processes and higher cost.
Method used
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Embodiment Construction
[0043]In an audio system with a charge pump to generate a negative supply voltage, the amplifiers to drive the output such as the line out, the headphone, or an earpiece, voltages across output transistors can become higher than their breakdown voltages. Stacking (also called cascoding) devices helps to make the circuits more robust. As illustrated in FIG. 2 and described above, conventional cascode devices are often biased with a constant voltage, halfway the supply voltage (or ground). This design may be adequate for quiescent operation and small output signals. However, as described below, with large signals, the voltage across the devices can be higher than the breakdown voltage limit of the transistors, thus requiring more costly devices with higher breakdown voltages.
[0044]FIG. 3 is a diagram illustrating the voltages at various circuit nodes in the output circuit in FIG. 2. In FIG. 3, the vertical axis shows the magnitude of the voltages at various circuit nodes, and the hori...
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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.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS[0001]NOT APPLICABLEBACKGROUND OF THE INVENTION[0002]The present invention relates generally to CMOS integrated circuit techniques. More specifically, embodiments of the present invention provide methods and circuits for protecting amplifier output circuits.[0003]Amplifier circuits are ubiquitous in modern electronic devices. An electronic amplifier increases the power and / or amplitude of a signal. In many applications, power amplifier circuits are used at the output stage of a system to drive an external device. Merely as an example, in an audio system, an output power amplifier is often used to drive an external speaker or headphone.[0004]Power amplifier circuits output stages can be classified as class A, B, AB, and C, etc. for analog signal amplification. This classification is based on the portion of the input signal cycle during which the amplifying device conducts.[0005]A Class A amplifier operates over the whole of the input cycle such...
Claims
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IPC IPC(8): H03F3/187H03F3/26
CPCH03F3/26H03F3/187H03F2200/219H03F2200/03H03F2200/426H03F1/523H03F3/303H03F2203/30084H03F2203/30117
Inventor NIELAND, JAN-HARM
Owner NUVOTON