JP5481262B2 - Audio signal processing circuit and electronic device using the same - Google Patents

Description

  The present invention relates to an audio signal processing circuit, and more particularly to a power supply technique for an amplifier that amplifies an audio signal.

  Various circuits such as amplifiers for driving headphones and speakers and drivers for liquid crystal panels require positive and negative power supply voltages for their operation. An inversion type charge pump circuit that generates a negative voltage from a battery voltage is used in small information terminals such as a mobile phone terminal, a PDA (Personal Digital Assistant), a digital camera, and a portable audio player (Patent Documents 1 to 3) reference).

  FIG. 1 is a circuit diagram showing a configuration of an audio system using a general positive / negative power source. The audio system 300 includes a head amplifier and a speaker amplifier (these are also collectively referred to as a main amplifier or a power amplifier) 302, an inverting charge pump circuit 304, and a speaker 306. The main amplifier 302 is, for example, an inverting amplifier, and inverts and amplifies the input voltage Vin and supplies the output voltage Vout to the speaker 306. Main amplifier 302 receives battery voltage Vdd as a positive power supply voltage. The inverting charge pump circuit 304 inverts the polarity of the battery voltage Vdd and generates the negative power supply voltage Vss of the main amplifier 302.

US Pat. No. 5,289,137 US Pat. No. 7,554,408B2 US Pat. No. 7,061,327

  When the main amplifier 302 is integrated, it is necessary to select the withstand voltage of the transistor in consideration of the difference (Vdd−Vss) between the power supply voltages supplied to the main amplifier 302. For example, if Vdd = 3.5V, the difference in power supply voltage is 7V, and a normal 5V breakdown voltage process cannot be used, and a high breakdown voltage process is required.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and one of exemplary objects of an aspect thereof is to provide an audio signal processing circuit that can be configured using a process with a relatively low breakdown voltage.

  One embodiment of the present invention relates to an audio signal processing circuit. The audio signal processing circuit inverts a positive power supply voltage and generates a negative power supply voltage whose absolute value is smaller than the positive power supply voltage, and a regulator circuit that steps down the positive power supply voltage. A main amplifier that receives the positive power supply voltage stepped down by the regulator circuit and the negative power supply voltage generated by the charge pump circuit and amplifies the input audio signal.

  According to this aspect, the difference between the positive and negative power supply voltages of the main amplifier can be reduced by optimizing the positive power supply voltage and the negative power supply voltage for the main amplifier by the regulator circuit and the charge pump circuit, respectively. It can be configured using a low breakdown voltage process.

  Another embodiment of the present invention is an electronic device. This electronic apparatus includes the above-described audio signal processing circuit.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to the present invention, the audio signal processing circuit can be configured by a low withstand voltage process.

It is a circuit diagram which shows the structure of the audio system using a general positive / negative power supply. It is a block diagram which shows the structure of the audio system which concerns on embodiment of this invention. FIG. 3 is an operation waveform diagram of the audio system of FIG. It is a block diagram which shows the structure of the audio system which concerns on a comparison technique.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected in addition to the case where the member A and the member B are physically directly connected. It includes the case of being indirectly connected through another member that does not affect the connection state.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through another member that does not affect the connection state.

  FIG. 2 is a block diagram showing a configuration of the audio system 1 according to the embodiment of the present invention. The audio system 1 is mounted on a battery-driven electronic device having an audio playback function and an audio output function such as a mobile phone terminal, a digital camera, a digital video camera, and a notebook PC. The audio system 1 includes a charge pump circuit 2, a main amplifier 4, a speaker 6, and a regulator circuit 8.

The charge pump circuit 2 inverts the polarity of a positive power supply voltage (battery voltage) Vdd from a battery (not shown) to generate a negative power supply voltage Vss. The absolute value of the negative power supply voltage Vss is smaller than the positive power supply voltage Vdd. That is, Vss> −Vdd is established. The charge pump circuit 2 itself has a function of regulating the output voltage Vss. The output voltage Vss of the charge pump circuit 2 may be fixed, or may be adaptively changed according to the amplitude of the audio signal S1 input to the audio system 1.
The charge pump circuit 2 may be a known or usable one in the future. For example, the technique described in Japanese Patent Application No. 2008-300458 can be suitably used.

  The regulator circuit 8 is a linear regulator or a switching regulator and steps down and stabilizes the positive power supply voltage Vdd. The power supply voltage Vdd ′ stabilized by the regulator circuit 8 is supplied to the main amplifier 4.

  The main amplifier 4 is supplied with a positive power supply voltage Vdd ′ that has been increased in voltage by the regulator circuit 8 and a negative power supply voltage Vss generated by the charge pump circuit 2. The main amplifier 4 amplifies the audio signal S1 output from the preceding circuit with a predetermined gain. The audio signal Vout amplified by the main amplifier 4 is supplied to a speaker 6 that is a load. The speaker 6 may be a headphone, an earphone or the like.

  The above is the configuration of the audio system 1. Next, the operation will be described. FIG. 3 is an operation waveform diagram of the audio system 1 of FIG. FIG. 3 shows the output voltage Vout of the main amplifier 302 that swings between the power supply voltage Vdd and the negative power supply voltage Vss and its envelope.

  The positive power supply voltage Vdd ′ is set as low as possible in a range higher than the maximum value of the output voltage Vout so that the audio signal is not distorted. Similarly, the negative power supply voltage Vss is set as high as possible in a range lower than the minimum value of the output voltage Vout. That is, the power supply voltages Vdd ′ and Vss are set so that ΔV1 and ΔV2 are as small as possible within a range where the audio signal is not distorted.

  For example, consider a case where the output voltage Vout of the main amplifier 4 swings in a voltage range of −Vdd / 2 to + Vdd / 2 at the maximum volume. At this time, the regulator circuit 8 generates a positive power supply voltage Vdd′≈Vdd / 2, and the charge pump circuit 2 generates a negative power supply voltage Vss≈−Vdd / 2.

  According to the audio system 1 of FIG. 2, the voltage applied between the positive and negative power supply terminals of the main amplifier 4 is sufficient as Vdd′−Vss = Vdd. Assuming that Vdd = about 3 to 5 V, the main amplifier 4 can be configured by a general 5 V breakdown voltage process.

  This advantage becomes clear by comparison with a configuration without the regulator circuit 8. When the regulator circuit 8 is not provided, assuming that Vss = −Vdd / 2, Vdd−Vss = 1.5 × Vdd is applied between the positive and negative power supply terminals of the main amplifier 4. Therefore, assuming that Vdd = 3 to 5V, a voltage of 4.5 to 7.5V is applied to the main amplifier 4, and therefore a 5V breakdown voltage process cannot be used. When a high breakdown voltage (7V breakdown voltage or 10V breakdown voltage) process is used, there is a problem that the cost increases. According to the audio system 1 of FIG. 2, the cost can be reduced.

  The advantage of providing the regulator circuit 8 at the position shown in FIG. 2 becomes clear by comparison with the comparison technique shown in FIG. FIG. 4 is a block diagram showing a configuration of the audio system 1a according to the comparison technique. In the audio system 1a, the regulator circuit 8a steps down the power supply voltage Vdd. The charge pump circuit 2 receives the stepped down power supply voltage Vdd 'and inverts it to generate a negative voltage Vss.

  4, the power supply voltage applied to the main amplifier 4 can be reduced similarly to the audio system 1a of FIG. 2, so that it may be possible to configure with a low withstand voltage process. However, in the configuration of FIG. 4, the current flowing through the positive power supply terminal of the main amplifier 4 and the current flowing through the negative power supply terminal both pass through the regulator circuit 8a. Therefore, the current capability required for the regulator circuit 8a is increased.

  Focusing on the audio system 1 in FIG. 2, the regulator circuit 8 only needs to supply a current flowing through the positive power supply terminal of the main amplifier 4. Therefore, the current supply capability is not required as much as the regulator circuit 8 a in FIG. 4. This means that the regulator circuit 8 of FIG. 2 can be made smaller than the regulator circuit 8a of FIG.

In addition, it has the following effects.
The power consumption of the main amplifier 4 can be reduced by making the negative power supply voltage Vss as high as possible by the charge pump circuit 2. When the regulator circuit 8 is a switching regulator, lowering the positive power supply voltage Vdd ′ also contributes to reduction of power consumption.

  In addition, by applying positive and negative power supply voltages to the main amplifier 4 and operating with the ground voltage (0 V) as a reference, a coupling capacitor is not required between the main amplifier 4 and the speaker 6, and the number of components can be reduced. In addition, since no coupling capacitor is required, the frequency characteristics can be improved.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Audio system, 2 ... Charge pump circuit, 4 ... Main amplifier, 6 ... Speaker, 8 ... Regulator circuit.

Claims (4)

A charge pump circuit that inverts a positive power supply voltage and generates a negative power supply voltage whose absolute value is smaller than the positive power supply voltage;
A regulator circuit for stepping down the positive power supply voltage;
A main amplifier that receives the positive power supply voltage stepped down by the regulator circuit and the negative power supply voltage generated by the charge pump circuit and amplifies the input audio signal;
Bei to give a,
An audio signal processing circuit , wherein a positive power supply voltage stepped down by the regulator circuit is equal to an absolute value of the negative power supply voltage generated by the charge pump circuit.   The audio signal processing circuit according to claim 1, wherein the charge pump circuit itself has a function of regulating the negative power supply voltage.   The sum of the absolute value of the negative power supply voltage generated by the charge pump circuit and the positive power supply voltage stepped down by the regulator circuit is less than or equal to a process breakdown voltage of the main amplifier. Item 3. The audio signal processing circuit according to Item 1 or 2. An electronic apparatus, comprising an audio signal processing circuit according to any one of claims 1 to 3.

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