Audio out unit

This application claims the benefit of U.S. Provisional Application No. 61/196,730, filed Dec. 15, 2008, the entirety of which is incorporated by reference herein.

1. Field of the Invention

The invention relates to an audio out unit, and in particular relates to a DC-coupled audio out unit with regulators at power terminals of audio amplifiers.

2. Description of the Related Art

FIG. 1 shows an audio out unit 100 with a headphone jack 50 . The audio out unit 100 comprises a right audio amplifier 101 and a left audio amplifier 102 which respectively receives and amplifies audio signals to respectively generate a right audio signal and a left audio signal. The headphone jack 50 comprises a first node N 1 to receive the right audio signal from the right audio amplifier 101 and a second node N 2 to receive the left audio signal from the left audio amplifier 102 and a third node N 3 to connect to a ground. Users can plug an earphone jack (not shown in FIG. 1 ) into the headphone jack 50 to receive the left and right audio signals, which are stereo audio signals.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

An embodiment of a DC-coupled audio out unit is provided. The DC-coupled audio out unit comprises a first regulator, a second regulator, and at least one audio amplifier. The first regulator receives a power source voltage to provide a positive power voltage. The second regulator receives the power source voltage to provide a negative power voltage. The audio amplifier receives the positive power voltage and the negative power voltage and amplifies at least one input signal to generate an audio output signal to an audio load.

Another embodiment of a DC-coupled audio out unit is provided. The DC-coupled audio out unit comprises a first regulator, a third regulator, a second regulator and at least one audio amplifier. The first regulator receives a power source voltage to provide a positive power voltage. The third regulator receives the power source voltage to provide an intermediate voltage. The second regulator receives the intermediate voltage to provide a negative power voltage. The audio amplifier receives the positive power voltage and the negative power voltage and amplifies at least one input signal to generate an audio output signal to an audio load.

Another embodiment of a DC-coupled audio out unit is provided. The DC-coupled audio out unit comprises a regulator and at least one audio amplifier. The regulator receives a first power source voltage to provide a negative power voltage. The audio amplifier receives a second power source voltage and the negative power voltage, and amplifies at least one input signal to generate an audio output signal to an audio load.

Another embodiment of a DC-coupled audio out unit is provided. The DC-coupled audio out unit comprises a first regulator, a voltage drive circuit, a second regulator and at least one audio amplifier. The first regulator receives a first supplied voltage to provide a control voltage. The voltage drive circuit is supplied by a power source voltage, and is arranged to generate a positive power voltage according to the control voltage. The second regulator receives an intermediate voltage to provide a negative power voltage. The audio amplifier receives the positive power voltage and the negative power voltage, and amplifies at least one input signal to generate an audio output signal to an audio load.

Another embodiment of a DC-coupled audio out unit is provided. The DC-coupled audio out unit comprises a first regulator, a first voltage drive circuit, a second regulator, a second voltage drive circuit, and at least one audio amplifier. The first regulator receives a first supplied voltage to provide a first control voltage. The first voltage drive circuit is supplied by a power source voltage and is arranged to generate a positive power voltage according to the first control voltage. The second regulator receives an second supplied voltage to provide a second control voltage. The second voltage drive circuit is supplied by a third supplied voltage and is arranged to generate a negative power voltage according to the second control voltage. The audio amplifier receives the positive power voltage and the negative power voltage, and amplifies at least one input signal to generate an audio output signal to an audio load.

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 shows an audio out unit with a headphone jack;

FIG. 2 shows an audio out unit with a headphone jack according to an embodiment of the invention;

FIG. 3A shows a DC-coupled audio out unit 300 A according to another embodiment of the invention;

FIG. 3B shows a DC-coupled audio out unit 300 B in a stereo system according to an embodiment of the invention;

FIG. 4A shows a DC-coupled audio out unit 400 A according to another embodiment of the invention;

FIG. 4B shows a DC-coupled audio out unit 400 B in a stereo system according to another embodiment of the invention;

FIG. 5A shows a DC-coupled audio out unit 500 A according to another embodiment of the invention;

FIG. 5B shows a DC-coupled audio out unit 500 B in a stereo system according to another embodiment of the invention;

FIG. 6A shows a DC-coupled audio out unit 600 A according to another embodiment of the invention;

FIG. 6B shows a DC-coupled audio out unit 600 B in a stereo system according to an embodiment of the invention;

FIG. 7 shows an embodiment of the regulator 601 and the voltage drive circuit 602 ;

FIG. 8A shows a DC-coupled audio out unit 800 A according to another embodiment of the invention;

FIG. 8B shows a DC-coupled audio out unit 800 B in a stereo system according to an embodiment of the invention;

FIG. 9A shows a DC-coupled audio out unit 900 A according to another embodiment of the invention;

FIG. 9B shows a DC-coupled audio out unit 900 B in a stereo system according to an embodiment of the invention;

FIG. 10A shows a DC-coupled audio out unit 1000 A according to another embodiment of the invention;

FIG. 10B shows a DC-coupled audio out unit 1000 B in a stereo system according to an embodiment of the invention;

FIG. 11 shows an audio amplifier according to another embodiment of the invention; and

FIG. 12 shows a charge pump circuit according to another embodiment of the invention.

The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims.

FIG. 2 shows an audio out unit 200 with a headphone jack 51 according to an embodiment of the invention. The audio out unit 200 comprises a right audio amplifier 201 and a left audio amplifier 202 which respectively receives and amplifies audio signals to generate a right audio signal S 101 and a left audio signal S 102 . The headphone jack 51 comprises a first node N 11 to receive the right audio signal S 101 from the right audio amplifier 201 and a second node N 12 to receive the left audio signal S 102 from the left audio amplifier 202 and a third node N 13 . The third node N 13 connects to a VCM buffer 203 (reference voltage unit) to receive a common-mode voltage or connects through a switch Sw 1 to a ground to receive a ground voltage. Thus, the third node N 13 is at the common mode voltage level or the ground voltage level controlled by the switch Sw 1 . For example, if the right audio signal S 101 and the left audio signal S 102 comprises a DC common mode voltage 0V, the switch Sw 1 is turned on so that the node N 13 connects to the ground and the third node N 13 is at 0V. If both of the right audio signal S 101 and the left audio signal S 102 comprise a DC common mode voltage 1.5V, the switch Sw 1 is turned off and the VCM buffer 203 provides a DC common mode voltage 1.5V.

FIG. 3A shows a DC-coupled audio out unit 300 A according to another embodiment of the invention. The DC-coupled audio out unit 300 A comprises a first regulator 301 , a second regulator 302 and an audio amplifier 310 . A power source voltage Vdd is generated by an outside voltage supplier or equipment (not shown in FIG. 3A ) and may be polluted by other power sources and coupled some interference signals. The first regulator 301 is coupled to the power source voltage Vdd and may be a linear regulator, such as a low-dropout regulator (LDO), reducing noise and ripples to generate a clean DC positive power voltage Vp 1 for the audio amplifier 310 . The second regulator 302 can be a switching regulator, such as either a charge pump circuit or an inductor based regulator, or a linear regulator, such as a low-dropout regulator (LDO). The second regulator 302 is also coupled to the power source voltage Vdd and reduces noise and ripples to generate a clean DC negative power voltage Vn 1 for the audio amplifier 310 . The audio amplifier 310 receives the positive power voltage Vp 1 and the negative power voltage Vn 1 and amplifies input signals S 301 and S 302 to generate an audio output signal S 300 to an audio load 315 .

As an example, assuming that the DC power source voltage Vdd is at 3.3V, the DC positive power voltage Vp 1 provided by the regulator is at 2.8V and the DC negative power voltage Vn 1 provided by the regulator 302 is at −1.4V. Absolute values of the positive power voltage Vp 1 and the negative power voltage Vn 1 can be different. Note that the audio output signal S 300 comprises a common-mode DC voltage 0V and a differential-mode AC voltage swinging between +1.2V to −1.2V. Since the common-mode DC voltage of the audio output signal 5300 is at 0V, no DC-blocking capacitor is required to be between the amplifier 310 and the audio load 315 for blocking DC voltage.

FIG. 3B shows a DC-coupled audio out unit 300 B in a stereo system according to an embodiment of the invention. Note that the elements labeled with the same numbers in FIG. 3A perform the same function. Unlike FIG. 3A , the right audio amplifier 310 A receives the positive power voltage Vp 1 and the negative power voltage Vn 1 and amplifies input signals S 304 and S 305 for the right channel to generate a right audio output signal S 303 to a right audio load 315 A, and the left audio amplifier 310 B receives the positive power voltage Vp 1 and the negative power voltage Vn 1 and amplifies input signals S 307 and S 308 for the left channel to generate a left audio output signal S 306 to a left audio load 315 B.

FIG. 4A shows a DC-coupled audio out unit 400 A according to another embodiment of the invention. The DC-coupled audio out unit 400 A comprises a first regulator 401 , a second regulator 402 , a third regulator 403 and an audio amplifier 410 . The first regulator 401 is coupled to the power source voltage Vdd and may be a linear regulator, such as an LDO, reducing noise and ripples to generate a clean DC positive power voltage Vp 1 for the audio amplifier 410 . The third regulator 403 may be a switching regulator, such as either a charge pump circuit or an inductor based regulator, generating a DC negative power voltage Vn 2 to the second regulator 402 . The second regulator 402 may be a linear regulator, such as an LDO, reducing noise and ripples to generate a clean DC negative power voltage Vn 1 for the audio amplifier 410 . The audio amplifier 410 receives the positive power voltage Vp 1 and the negative power voltage Vn 1 and amplifies input signals S 401 and S 402 to generate an audio output signal S 400 to an audio load 415 .

FIG. 4B shows a DC-coupled audio out unit 400 B in a stereo system according to another embodiment of the invention. Note that the elements labeled with the same numbers in FIG. 4A perform the same function. Unlike FIG. 4A , the right audio amplifier 410 A receives the positive power voltage Vp 1 and the negative power voltage Vn 1 and amplifies input signals S 404 and S 405 for the right channel to generate a right audio output signal S 403 to a right audio load 415 A, and the left audio amplifier 410 B receives the positive power voltage Vp 1 and the negative power voltage Vn 1 and amplifies input signals S 407 and S 408 for the left channel to generate a left audio output signal S 406 to a left audio load 415 B.

FIG. 5A shows a DC-coupled audio out unit 500 A according to another embodiment of the invention. The DC-coupled audio out unit 500 A comprises a regulator 501 and an audio amplifier 510 . The regulator 501 is coupled to a power source voltage VS and may be a linear regulator, such as an LDO, reducing noise and ripples to generate a clean DC negative power voltage Vn 1 for the audio amplifier 510 . When the regulator 501 is a linear regulator, the power source voltage VS is of a negative voltage level. In another embodiment, the regulator 501 may be a switching regulator, such as either a charge pump circuit or an inductor based regulator. When the regulator 501 is a switching regulator, the power source voltage VS may be realized by the voltage Vdd shown in FIG. 5A or another voltage level independent of the voltage Vdd. The audio amplifier 510 receives the positive power source voltage Vdd and the negative power voltage Vn 1 and amplifies input signals S 501 and S 502 to generate an audio output signal S 500 to an audio load 515 .

FIG. 5B shows a DC-coupled audio out unit 500 B in a stereo system according to another embodiment of the invention. Note that the elements labeled with the same numbers in FIG. 5A perform the same function. Unlike FIG. 5A , the right audio amplifier 510 A receives the positive power source voltage Vdd and the negative power voltage Vn 1 and amplifies input signals S 504 and S 505 for the right channel to generate a right audio output signal S 503 to a right audio load 515 A, and the left audio amplifier 510 B receives the positive power source voltage Vdd and the negative power voltage Vn 1 and amplifies input signals S 507 and S 508 for the left channel to generate a left audio output signal S 506 to a left audio load 515 B.

FIG. 6A shows a DC-coupled audio out unit 600 A according to another embodiment of the invention. The DC-coupled audio out unit 600 A comprises a regulator 601 , a voltage drive circuit 602 , a regulator 603 and an audio amplifier 610 . The regulator 601 receives a supplied voltage VS 1 to provide a control voltage Vc. The voltage drive circuit 602 is supplied by a power source voltage Vdd and is arranged to generate a positive power voltage Vp 1 according to the control voltage Vc. The regulator 602 receives a voltage VS 2 to provide a negative power voltage Vn 1 . The audio amplifier 610 receives the positive power voltage Vp 1 and the negative power voltage Vn 1 , and amplifies input signals S 601 and S 602 to generate an audio output signal S 600 to an audio load 615 .

FIG. 7 shows an embodiment of the regulator 601 and the voltage drive circuit 602 . The regulator 601 may be a linear regulator, such as an LDO, reducing noise and ripples of the supplied voltage VS 1 to guarantee that the control voltage Vc is clean. The voltage drive circuit 602 coupled between the regulator 601 and the power terminal of the audio amplifier blocks the regulator 601 from voltage vibrations, caused by huge current drawn by the audio amplifier, at the power terminal of the audio amplifier. The voltage drive circuit 602 allows the regulator 601 to be realized by low cost regulators. The supplied voltage VS 1 may be realized by the power source voltage Vdd that powers the voltage drive circuit 602 , or may be realized by another voltage level independent of the power source voltage Vdd.

Referring back to FIG. 6A , the regulator 603 is powered by a voltage VS 2 . In the embodiments when the regulator 603 is a linear regulator, such as an LDO, and the voltage VS 2 is of a negative voltage level, the regulator 603 reduces noise and ripples of the negative voltage level VS 2 to generate the negative power voltage Vn 1 . In another embodiment when the regulator 603 is a switching regulator, such as either a charge pump circuit or an inductor based regulator, the voltage VS 2 may be realized by the power source voltage Vdd that powers the voltage drive circuit 602 , or may be realized by the supplied voltage VS 1 that powers the regulator 601 , or may be designed to be another voltage level independent of the supplied voltage VS 1 and the power source voltage Vdd.

FIG. 6B shows a DC-coupled audio out unit 600 B in a stereo system according to another embodiment of the invention. Note that the elements labeled with the same numbers in FIG. 6A perform the same function. Because the regulator 601 is blocked from the huge current drawn by the audio amplifier 610 A or 610 B, the right and left audio amplifiers 610 A and 610 B may share the regulator 601 and the two voltage drive circuits 602 A and 602 B are separately designed for the right and left audio. According to the control voltage Vc, the voltage drive circuits 602 A and 602 B generate positive power voltages Vp 1 A and Vp 1 B, respectively, for the right and left audio amplifiers 610 A and 610 B. The sharing of the first regulator 601 reduces considerable circuit size of the audio out unit 600 B. The right audio amplifier 610 A receives the positive power voltage Vp 1 A and the negative power voltage Vn 1 and amplifies input signals S 604 and S 605 for the right channel to generate a right audio output signal S 603 to a right audio load 615 A, and the left audio amplifier 610 B receives the positive power voltage Vp 1 B and the negative power voltage Vn 1 and amplifies input signals S 607 and S 608 for the left channel to generate a left audio output signal S 606 to a left audio load 615 B.

FIG. 8A shows a DC-coupled audio out unit 800 A according to another embodiment of the invention. Compared with the embodiment shown in FIG. 6A , FIG. 8A further comprises a switching regulator 801 , such as either a charge pump circuit or an inductor based regulator. The switching regulator 801 is powered by a voltage VS 2 to generate an intermediate voltage Vn 2 to power the regulator 603 . In this case, the voltage VS 2 may be realized by the power source voltage Vdd that powers the voltage drive circuit 602 , or may be realized by the supplied voltage VS 1 that powers the regulator 601 , or another voltage level independent of the supplied voltage VS 1 and the power source voltage Vdd. Furthermore, the regulator 603 may be a linear regulator, such as an LDO, reducing noise and ripples of the intermediate voltage Vn 2 to generate a cleans negative power voltage Vn 1 . The audio amplifier 810 receives the positive power voltage Vp 1 and the negative power voltage Vn 1 , and amplifies input signals S 801 and S 802 to generate an audio output signal S 800 to an audio load 815 .

FIG. 8B shows a DC-coupled audio out unit 800 B in a stereo system according to another embodiment of the invention. Note that the elements labeled with the same numbers in FIG. 8A perform the same function. Unlike FIG. 8A , the right audio amplifier 810 A receives the positive power voltage Vp 1 A and the negative power voltage Vn 1 and amplifies input signals S 804 and S 805 for the right channel to generate a right audio output signal S 803 to a right audio load 815 A, and the left audio amplifier 810 B receives the positive power voltage Vp 1 B and the negative power voltage Vn 1 and amplifies input signals S 807 and S 808 for the left channel to generate a left audio output signal S 806 to a left audio load 815 B.

FIG. 9A shows a DC-coupled audio out unit 900 A according to another embodiment of the invention. Compared with the embodiment shown in FIG. 6A , the DC-coupled audio out unit 900 A uses a regulator 901 and a voltage drive circuit 902 to generate the negative power voltage Vn 1 for the negative power terminal of the audio amplifier 910 . The regulator 901 is powered by a voltage VS 2 to generate a control voltage 903 . The voltage drive circuit 902 is powered by a voltage VS 3 to generate the negative power voltage Vn 1 according to the control voltage 903 . In an embodiment when the regulator 901 is a linear regulator, such as an LDO, the voltages VS 2 and VS 3 are negative, and may be of the same voltage level or of distinct voltage levels. In another embodiment when the regulator 901 is a switching regulator, such as either a charge pump circuit or an inductor based regulator, the voltage VS 2 may be realized by the voltage VS 1 that powers the regulator 601 , or may be realized by the power source voltage Vdd that powers the voltage drive circuit 602 , or may be another voltage independent of the voltages Vdd and VS 1 , and the voltage VS 3 is a negative voltage. The audio amplifier 910 receives the positive power voltage Vp 1 and the negative power voltage Vn 1 , and amplifies input signals S 901 and S 902 to generate an audio output signal S 900 to an audio load 915 .

FIG. 9B shows a DC-coupled audio out unit 900 B in a stereo system according to another embodiment of the invention. Note that the elements labeled with the same numbers in FIG. 9A perform the same function. As shown, the right and left audio amplifiers 910 A and 910 B may share the regulator 901 and the two voltage drive circuits 902 A and 902 B are separately designed for the right and left audio. According to the control voltage 903 , the voltage drive circuits 902 A and 902 B generate negative power voltages Vn 1 A and Vn 1 B, respectively, for the right and left audio amplifiers 910 A and 910 B. The sharing of the regulator 901 reduces considerable circuit size of the audio out unit 900 B. The right audio amplifier 910 A receives the positive power voltage Vp 1 A and the negative power voltage Vn 1 A and amplifies input signals S 904 and S 905 for the right channel to generate a right audio output signal S 903 to a right audio load 915 A, and the left audio amplifier 910 B receives the positive power voltage Vp 1 B and the negative power voltage Vn 1 B and amplifies input signals S 907 and S 908 for the left channel to generate a left audio output signal S 906 to a left audio load 915 B.

FIG. 10A shows a DC-coupled audio out unit 1000 A according to another embodiment of the invention. Compared with the embodiment shown in FIG. 9A , the DC-coupled audio out unit 1000 A further comprises a switching regulator 1001 , such as either a charge pump circuit or an inductor based regulator. The switching regulator 1001 is powered by a voltage VS 4 to generate a voltage VS 2 to power the regulator 901 . In this case, the voltage VS 4 may be realized by the power source voltage Vdd that powers the voltage drive circuit 602 , or the supplied voltage VS 1 that powers the regulator 601 , or another voltage level independent of the supplied voltage VS 1 and the power source voltage Vdd, the regulator 901 may be a linear regulator, such as an LDO, and the voltage VS 3 is negative. The audio amplifier 1010 receives the positive power voltage Vp 1 and the negative power voltage Vn 1 , and amplifies input signals S 1001 and S 1002 to generate an audio output signal S 1000 to an audio load 1015 .

FIG. 10B shows a DC-coupled audio out unit 1000 B in a stereo system according to another embodiment of the invention. Note that the elements labeled with the same numbers in FIG. 10A perform the same function. As shown, the right and left audio amplifiers 1010 A and 1010 B may share the switching regulator 1001 and the regulator 901 , and the two voltage drive circuits 902 A and 902 B are separately designed for the right and left audio. According to the control voltage 903 , the voltage drive circuits 902 A and 902 B generate negative power voltages Vn 1 A and Vn 1 B, respectively, for the right and left audio amplifiers 1010 A and 1010 B. The sharing of the switching regulator 1001 and the regulator 901 reduces considerable circuit size of the audio out unit 1000 B. The right audio amplifier 1010 A receives the positive power voltage Vp 1 A and the negative power voltage Vn 1 A and amplifies input signals S 1004 and S 1005 for the right channel to generate a right audio output signal S 1003 to a right audio load 1015 A, and the left audio amplifier 1010 B receives the positive power voltage Vp 1 B and the negative power voltage Vn 1 B and amplifies input signals S 1007 and S 1008 for the left channel to generate a left audio output signal S 1006 to a left audio load 1015 B.

According to the above embodiments of the invention, the audio amplifiers can receive clean positive and negative power voltages Vp 1 and Vn 1 to generate the audio output signals without interference and noise to the audio loads.

FIG. 11 shows an audio amplifier 1100 according to another embodiment of the invention. The audio amplifier 1100 comprises a first-stage amplifier 1110 , a second-stage amplifier 1120 and an output driver 1130 . The output driver 1130 is composed of a PMOS transistor M 1 and an NMOS transistor M 2 . The first-stage amplifier 1110 receives and amplifies audio signals S 1101 and S 1102 (may be S 301 and S 302 , S 401 and S 402 , S 501 and S 502 , S 601 and S 602 , S 801 and S 802 , S 901 and S 902 , or S 1001 and S 1002 ) to generate differential audio signals S 1111 and S 1112 to the second-stage amplifier 1120 . The second-stage amplifier 1120 receives and amplifies the audio signals S 1111 and S 1112 to generate differential audio signal S 1121 and S 1122 to the output driver 1130 . The output driver 1130 receives the audio signals S 1121 and S 1122 to generate the audio output signal S 1100 (may be S 300 , S 400 , S 500 , S 600 , S 800 S 900 or S 1000 ) which swings between +1.2V to −1.2V to the audio load.

FIG. 12 shows a charge pump circuit 1200 according to another embodiment of the invention. The charge pump circuit 1200 can be used as the aforementioned switching regulator. The charge pump circuit 1200 receives a clock signal CLK, the power source voltage Vdd and the ground voltage GND and generates a negative DC power voltage at a node N 1200 . The charge pump circuit comprises an inverter 1210 and diodes 1221 and 1222 , which are connected as shown in FIG. 12 . The charge pump circuit 1200 needs to couple to two outside capacitors C 1 and C 2 to provide negative voltage at the node N 1200 . The capacitor C 1 is coupled between the inverter 1210 and the diodes 1221 . The diode 1222 is coupled between the capacitor C 1 and the capacitor C 2 , as shown in FIG. 12 . The capacitor C 2 is coupled between the diode 1222 and the ground. The capacitor C 1 and C 2 are small capacitors, such as 2.2 uF capacitors. Thus, the capacitors C 1 and C 2 do not occupy too much circuit area.

While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited to thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.