Audio playing systems

An audio playing system is provided comprising a first processing module, a second processing module, a control module, an output module, and a displaying module. The first and second processing modules amplify an audio signal and respectively generates a first first processed signal, a first second processed signal, a second first processed signal, and a second second processed signal. The control module is coupled to the first processing module and the second processing module and generates a playing signal according to a control signal, the first first processed signal, the first second processed signal, the second first processed signal, and the second second processed signal. The output module is coupled to the control module and amplifies the playing signal to generate an output signal. The displaying module is coupled to the output module and plays the output signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an audio playing system, and more particularly to an audio playing system preventing electromagnetic interference (EMI).

2. Description of the Related Art

Currently, audio signal amplifiers are implemented mainly by Class D amplifiers. A Class AB amplifier, a formerly implemented amplifier, generates a linear signal, and a Class D amplifier generates a pulse-width modulation (PWM) signal which comprises audio frequency signals, a PWM switch signal, and PWM harmonic waves. When a Class D amplifier operates, the metal-oxide semiconductor field-effect transistor (MOSFET) impedance during an output stage switches to low from high, and the MOSFET operates in the active region for a few seconds. Thus, power consumption for an output stage of a Class D amplifier is much lower than that of a Class AB amplifier. Moreover, an inductor plus capacitor (LC) filter within the Class D amplifier saves enough power during each operating period of the Class D amplifier, so that power consumption when the Class D amplifier is turned on or off does not occur in speakers connected to the Class D amplifier.

However, electromagnetic interference (EMI) is a problem for a Class D amplifier. Because operations, such as turning on and off transistors, are continuously performed in a Class D amplifier, EMI may occur more easily. When a Class D amplifier is used to drive an earphone, connection lines of the earphone exacerbate EMI. Thus, improving the problem of EMI for a Class D amplifier and enhancing quality of audio played by an audio signal amplifier are important issues.

BRIEF SUMMARY OF THE INVENTION

An exemplary embodiment of an audio playing system comprises a first processing module, a second processing module, a control module, an output module, and a playing module. The first processing module amplifies an audio signal and generates a first first processed signal and a first second processed signal respectively at a first first output terminal and a first second output terminal. The second processing module amplifies the audio signal and generates a second first processed signal and a second second processed signal respectively at a second first output terminal and a second second output terminal. The control module is coupled to the first processing module and the second processing module and generates a playing signal according to a control signal, the first first processed signal, the first second processed signal, the second first processed signal, the second second processed signal. The output module is coupled to the control module and amplifies the playing signal to generate an output signal. The playing module is coupled to the output module and plays the output signal.

DETAILED DESCRIPTION OF THE INVENTION

Audio playing systems are provided. In an exemplary embodiment of an audio playing system shown inFIG. 1, an audio playing system10comprises a first processing module11, a second processing module12, a control module14, an output module16, and a playing module18. The first processing module11amplifies an audio signal and generates a first first processed signal S11and a first second processed signal S12respectively at a first first output terminal111and a first second output terminal112. The second processing module12amplifies the audio signal and generates a second first processed signal S21and a second second processed signal S22respectively at a second first output terminal121and a second second output terminal122. The control module14is coupled to the first processing module11and the second processing module12and generates a playing signal SPLaccording to a control signal SC, the first first processed signal S11, the first second processed signal S12, the second first processed signal S21, and the second second processed signal S22. The output module16is coupled to the control module14and amplifies the playing signal SPLto generate an output signal SO. The playing module18is coupled to the output module15and plays the output signal SO. In some embodiments, the first processing module11is a pre-driver of a Class D audio signal amplifier, and the second processing module12is a pre-driver of a Class AB audio signal amplifier. The playing module18can be a speaker or an earphone. In the embodiment, the phase difference between the first first processed signal S11and the first second processed signal S12is 180 degrees, and the phase difference between the second first processed signal S21and the second second processed signal S22is 180 degrees.

Additionally, the output module16of the audio playing system10comprises a determination unit20coupled to the control module14and the playing module18. The determination unit20determines whether the playing module18is an earphone and generates the control signal SCaccording to the determined result. In some embodiments, the determination unit20comprises an output pin (not shown inFIG. 1) which is used to couple to an input terminal of the earphone. The determination unit20determines whether the playing module18is an earphone according to whether the output pin couples to the input terminal of the earphone or not. If the playing module18is an earphone, the control signal SCis generated. When the determination unit20determines that the playing module18is an earphone, the control module14is controlled by the generated control signal SCto generate the playing signal SPLaccording to the second first processed signal S21and the second second processed signal S22. When the determination unit20determines that the playing module18is not an earphone, the control module14generates the playing signal SPLaccording to the first first processed signal S11and the first second processed signal S12. The circuit of the determination unit20can be composed of a resistor coupled to a ground. When the input terminal of an earphone is coupled to the output pin, a current is generated. Thus, it is known that an earphone is inserted into the output pin, and the playing module18is determined as an earphone. Thus, completing an example for the operation of the determination unit20. Any circuit for determining whether two devices are coupled to each other can be implemented as the determination unit20. Thus, the determination unit20is not limited to above example.

FIG. 2is another exemplary embodiment of an audio playing system. In the embodiment ofFIG. 2, for example, the playing module18is a speaker. The control module14comprises a first switch SW1and a second switch SW2. One terminal of the first switch SW1is coupled to the output module16, and the other terminal thereof is selectively coupled to the first first output terminal111of the first processing module11or the second first output terminal121of the second processing module12according to the control signal SC. One terminal of the second switch SW2is coupled to the output module16, and the other terminal thereof is selectively coupled to the first second output terminal112of the first processing module11or the second second output terminal122of the second processing module12according to the control signal SC.

The output module16comprises a transistor set162, an inductance164, and a capacitor166. A first input terminal of the transistor set162is coupled to the first switch SW1, a second input terminal thereof is coupled to the second switch SW2. A first terminal of the inductance164is coupled to an output terminal of the transistor set162. A first terminal of the capacitor166is coupled to a second terminal of the inductance164, and a second terminal thereof is coupled to a ground GND. The transistor set162amplifies the playing signal SPL. The inductance164and the capacitor166work together to filter the amplified play signal SPLto generate the output signal SO.

The transistor set162comprises a first transistor1621and a second transistor1622. A gate of the first transistor1621is coupled to the first input terminal of the transistor set162, a source thereof is coupled to a voltage source VCC, and a drain thereof is coupled to the output terminal of the transistor set162. A gate of the second transistor1622is coupled to the second input terminal of the transistor set162, a source thereof is coupled to the ground GND, and a drain thereof is coupled to the output terminal of the transistor set162.

According to the embodiment of the invention, the audio playing system comprises both, a Class D audio signal amplifier and a Class AB audio signal amplifier. When the load is determined to be a speaker, the audio playing system processes the audio signal using the Class D audio signal amplifier and plays the processed signal through the speaker. When the load is determined to be an earphone, the audio playing system is switched to use the Class AB audio signal amplifier for processing and plays the processed signal through the earphone. Thus, serious EMI caused by using a Class D audio signal amplifier to drive an earphone can be prevented, so that quality and audio signal playing effect can be enhanced. For the invention, with the exception of the inductor and the capacitor of the output module and the playing module, other elements of the invention can be disposed within an integrated circuit, thus reducing size of the entire circuit.