Patent Grant
9338570
The present invention relates generally to electronic circuits for audio systems. More particularly, embodiments of the present invention provide circuits and systems for an integrated headset switch with reduced crosstalk noise.
With the advancement of electronics and integrated circuits, great progress has also been made in audio systems used in entertainment, computer systems, communication, electronic games, and mobile computing devices, etc. In advanced audio systems with features such as stereo sound, 3-D sound, and noise cancelation, the demand for quality is even higher. The quality of an audio system is measured by many parameters, for example, frequency response, harmonic distortion, output power, noise, and crosstalk, etc.
In electronics, crosstalk occurs when a signal transmitted on one circuit or channel of a system creates an undesired effect in another circuit or channel. Crosstalk is usually caused by undesired coupling from one circuit to another and can be especially prevalent in audio systems that include multiple speakers and/or a microphone. For example, headphones are a pair of small loudspeakers that are designed to be held close to a user's ears. Headphones either have wires or have a wireless receiver for connection to a signal source such as an audio amplifier, radio, CD player, portable media player, or mobile phone. Modern headphones have been particularly widely sold and used for listening to stereo recordings. Headphones are also useful for video games that use 3D positional audio processing algorithms, as they allow players to better judge the position of an off-screen sound source.
Multiple speakers are also used in surround sound, which is a technique for enriching the sound reproduction quality of an audio source with additional audio channels from speakers that surround the listener. Typically this is achieved by using multiple discrete audio channels routed to an array of loudspeakers.
Modern headsets often include a microphone for voice inputs in applications such as mobile devices and computers. The inclusion of a microphone in a headset can further complicate performance issues including crosstalk.
As described below, an audio system having two or more speakers and a microphone often are susceptible to crosstalk noise. Therefore, improved techniques for reducing the crosstalk noise in an audio system are highly desired.
The present invention relates generally to electronic circuits for audio systems. More particularly, embodiments of the present invention relate to circuits and systems for an integrated headset switch with reduced crosstalk noise. Merely, by way of example, embodiments of the present invention have been applied to a headset having two speakers and a microphone sharing a ground connection, but it would be recognized that the invention has a much broader range of applications and can be applied to other audio systems as well.
According to an embodiment of the present invention, an integrated audio signal processing circuit is described for reducing crosstalk noise in an audio system including, for example, a headset having a first and a second speakers, a microphone sharing a common ground. The audio signal processing circuit includes first, second, third, and fourth terminals for coupling to a headset having a first and a second speakers, a microphone, and a headset ground. The first and the second terminals are configured for providing a first and a second audio signals to the first and the second speakers, respectively. The third and the fourth terminals are configured to be either a microphone connection terminal or a headset ground connection terminal, respectively, depending on the type of the headset. The audio signal processing circuit also includes an audio jack detection circuit configured to detect the headset ground connection terminal and to provide a corresponding headset ground selection signal indicating whether the third or the fourth terminals is the headset ground connection terminal or the microphone connection terminal.
The audio signal processing circuit also has first and second audio amplifiers for providing the first and the second audio signals to the first and second terminals, respectively. An audio amplifier reference node is coupled to inputs of the first and the second audio amplifiers for providing a common mode signal. Further, the audio signal processing circuit has a first switch device responsive to the headset ground selection signal and configured to connect the audio amplifier reference node to the detected headset ground connection terminal. The audio signal processing circuit also has a second switch device responsive to the headset ground selection signal and configured to couple the detected headset ground connection terminal to a ground terminal of the audio processing circuit. In some embodiments, the audio signal processing circuit also includes a third switch device responsive to the headset ground selection signal and configured to couple the microphone connection terminal to a microphone bias circuit and a fourth switch device responsive to the headset ground selection signal and configured to couple the microphone connection terminal to a push button signal detection circuit.
As described above, in the headset, the first and the second speakers and the microphone are coupled to the headset ground, wherein, in the audio processing circuit. Therefore, the headset is susceptible crosstalk noise. In embodiments of the present invention, the first and the second switch devices are configured such that the differential voltage across the first speaker remains zero when the second speaker contains a non-zero signal, and such that the differential voltage across the second speaker remains zero when the first speaker contains a non-zero signal.
In some embodiments, the audio signal processing circuit also includes a signal processing circuit.
In some embodiments, the audio signal processing circuit also includes a microphone input amplifier configured for being coupled to the third and the fourth terminals of the headset for receiving an AC microphone input signal. In a specific embodiment, the microphone input amplifier is configured to be coupled to the third and fourth terminals of the headset through a first and a second blocking capacitors.
In some embodiments of the invention, the first switch device includes first and second MOS transistors. In another embodiment, the second switch device includes third and fourth MOS transistors.
According to another embodiment of the present invention, an audio system, includes a headset having a first and a second speakers, a microphone, and a headset ground. A headset plug has first, second, third, and fourth terminals for coupling the first and second speakers, the microphone, and the headset ground, respectively. An audio jack is configured for receiving the headset plug, and an audio signal processing circuit coupled to the audio jack. The audio signal processing circuit includes first, second, third, and fourth terminals for coupling to the headset through the audio jack and the headset plug. The first and the second terminals are configured for providing a first and a second audio signals to the first and the second speakers, respective. The third and the fourth terminals are configured to be either a microphone connection terminal or a headset ground connection terminal, respectively, depending on the type of the headset. An audio jack detection circuit is configured to detect the headset ground connection terminal and to provide a corresponding headset ground selection signal. A first and a second audio amplifiers provide the first and the second audio signals to the first and second terminals, respectively. An audio amplifier reference node is coupled to inputs of the first and the second audio amplifiers for providing a common mode signal. The audio processing circuit also has a first switch device responsive to the headset ground selection signal and configured to connect the audio amplifier reference node to the detected headset ground connection terminal, and a second switch device responsive to the headset ground selection signal and configured to couple the detected headset ground connection terminal to a ground terminal of the audio processing circuit.
In some embodiments of the audio system, the an audio signal processing circuit also includes a third switch device responsive to the headset ground selection signal and configured to couple the microphone connection terminal to a microphone bias circuit for providing a bias to an electret microphone.
In another embodiment, the an audio signal processing circuit also has a fourth switch device responsive to the headset ground selection signal and configured to couple the microphone connection terminal to a push button signal detection circuit.
In another embodiment, the integrated audio signal processing circuit further includes a microphone input amplifier configured for coupling to the third and the fourth terminals of the headset for receiving an AC microphone input signal.
In yet another embodiment, the audio system also includes a first and a second blocking capacitors, wherein the microphone input amplifier is configured to be coupled to the third and fourth terminals of the headset through the first and the second blocking capacitors.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.
The description below refers to a series of drawing figures enumerated above. These diagrams are merely examples, and should not unduly limit the scope of the claims herein. In connection with the various aspects illustrated and described, one of ordinary skill in the art would recognize other variations, modifications, and alternatives.
Headset plug 120 has four terminals, sometimes referred to as tip, ring 1, ring 2, and sleeve (TRRS) connectors. In headset plug 120, the first terminal 121 and the second terminal 122, connected to pin 1 and pin 2 of headset 110, are configured for providing a first and a second audio signals to the first and the second speakers, 111 and 112, respectively. The third and the fourth terminals of the headset plug, 123 and 124, connected to two pins both labeled pin 3/4, are configured to be coupled either to the microphone 114 or the ground 116 of the headset depending on the type of the headset plug. For example,
As shown in
As described above, different headsets can have different microphone and ground pin connections. Therefore, audio driver circuit needs to be able to switch between the different pin connections. These switches often have built-in resistance. As shown in
Therefore, there is a need for improved methods for the reduction of crosstalk noise in an audio system.
According to embodiments of the present invention, integrated audio signal processing circuit 300 is configured for reducing crosstalk noise in an audio system including, for example, a headset having a first and a second speakers, and a microphone sharing a common ground, as depicted in
Audio signal processing circuit also includes an audio jack detection circuit 310 configured to detect the headset ground connection terminal and to provide a corresponding headset ground selection signal 312, which indicates either terminal 303 or 304 is the headset ground connection terminal or the headset microphone connection terminal. In an embodiment, audio jack detection circuit 310 is configured to detect the ground connection by measuring the impedance between the terminals. For example, in some headset, the resistance between the speaker terminals and the ground terminals may have a different value than the resistance between the microphone terminal and the ground terminal. Of course, other conventional audio jack detection methods can also be used.
Audio signal processing circuit 300 also has first and second audio amplifiers 321 and 322 for providing the first and the second audio signals to the first and second terminals, 301 and 302, respectively. In
Further, the audio signal processing circuit has a first switch device 331 responsive to the headset ground selection signal 312 and configured to connect the audio amplifier reference node hpcom to the detected headset ground connection terminal, either terminals 303 or 304. The audio signal processing circuit also has a second switch device 332 responsive to the headset ground selection signal 312 and configured to couple the detected headset ground connection terminal to a ground terminal MCGND of the audio processing circuit.
In some embodiments, the audio signal processing circuit also includes a third switch device (333) responsive to the headset ground selection signal 312 and configured to couple the microphone connection terminal, either terminals 303 or 304, to a microphone bias circuit 327). The microphone bias circuit typically requires a low noise high power supply rejection amplifier to provide a bias voltage MCBS to an electret microphone. The voltage is then supplied to the microphone through one of the resistors connected to switch device 333. In some embodiments, the audio signal processing circuit also includes a fourth switch device 334 responsive to the headset ground selection signal and configured to couple the microphone connection terminal, either terminals 303 or 304, to a push button signal detection circuit 328 for detecting push button signal, e.g., a Send/End signal in some headsets. The SAR ADC in push button signal detection circuit 328 is used to detect push buttons on the microphone pin and the SAR ADC data is processed by the logic circuits in order to detect valid push button presses.
As described above, in the headset, the first and the second speakers and the microphone are coupled to the headset ground. Further, the ground connections of first and second audio amplifiers are made through selection switch 332, which has finite resistances and is connected to either terminal 303 or terminal 304 depending on the type of the headset plug. Since switch 331 has a finite resistance, a current on one of the speakers can produce a voltage that would appear on the other speaker, because the ground is shared by second speaker. Therefore, the headset is susceptible to crosstalk noise. However, in embodiments of the invention, audio amplifier reference node hpcom is connected to the detected headset ground connection terminal as shown in
In some embodiments, the audio signal processing circuit also includes a signal processing circuit 350 that can include circuits such as a CODEC (coder/decoder) for processing audio signals and circuits for interfacing with audio equipment or a computer system. To simplify the drawing, connections to signal processing circuit 350 are omitted in
In some embodiments, the audio signal processing circuit also includes a microphone input amplifier 323 PGA (programmable gain amplifier), which is configured for coupling to the third and the fourth terminals 303 and 304 of the headset for receiving an AC microphone input signal. The PGA output typically goes to an audio ADC for audio processing, but may also be used directly as an analog audio output. In a specific embodiment, the microphone input amplifier is configured to be coupled to the third and fourth terminals of the headset through a first and a second blocking capacitors 341 and 342.
In some embodiments, switch devices 301-304 in
As described above, in the headset, the first and the second speakers and the microphone are coupled to the headset ground. Therefore, the headset is susceptible crosstalk noise. Further, in the audio processing circuit, switch devices are used for connections to the selected headset ground terminal. The resistance of the switch devices also can cause crosstalk problems. In embodiments of the present invention, the internal headphone amplifier reference is tied to an internal ground reference that is derived from either pin 3 or pin 4 of the headset, such that the differential voltage across the left speaker remains zero when the right speaker contains a non-zero signal and such that the differential voltage across the right speaker remains zero when the left speaker contains a non-zero signal.
While the above is a description of specific embodiments of the invention, the above description should not be taken as limiting the scope of the invention. It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
| Number | Name | Date | Kind |
|---|---|---|---|
| 8150046 | Hansson | Apr 2012 | B2 |
| 8917882 | Miao | Dec 2014 | B2 |
| 20110268289 | Baranwal | Nov 2011 | A1 |
| 20120237044 | Poulsen | Sep 2012 | A1 |
| 20140010398 | Wang | Jan 2014 | A1 |
| 20140029770 | Chien | Jan 2014 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20150098579 A1 | Apr 2015 | US |
