JP4197988B2 - Audio playback device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital amplifier that digitally amplifies an input signal and an audio reproduction apparatus using the digital amplifier.
[0002]
[Prior art]
In recent years, digital amplifiers (class D amplifiers, etc.) that are more power efficient than analog amplifiers (class A amplifiers, etc.) have begun to be mounted on audio playback devices against the backdrop of advances in modulation / demodulation technology and improved response of power elements. In particular, the applicant of the present application includes a ΔΣ converter that converts an analog audio signal or a multi-bit digital audio signal into a 1-bit digital audio signal, a switching amplifier that amplifies (amplifies) the 1-bit digital audio signal, and an amplification A 1-bit digital amplifier comprising a digital / analog conversion unit for converting the 1-bit digital audio signal into an analog signal is disclosed and proposed (see, for example, Patent Document 1), and an audio reproduction equipped with the amplifier is provided. The device has been put to practical use.
[0003]
The 1-bit digital amplifier uses a ΔΣ modulation method as means for improving the S / N of the audible band (means for reducing audible band noise), and noise is reduced by noise shaping on the 1-bit signal generation side. The audible band noise is reduced by moving the audible band noise on the floor (the noise layer near the lower part of the signal level) to the high band side. Therefore, if the order of the ΔΣ modulation system is increased, the audible band noise reduction effect can be increased, and if the ΔΣ modulation system sampling frequency is increased, the frequency band where the noise reduction effect can be expanded can be expanded. (See FIGS. 2 (a) and 2 (b)).
[0004]
[Patent Document 1]
JP 2002-246852 A [Patent Document 2]
Japanese Patent Laid-Open No. 2003-37481
[Problems to be solved by the invention]
Certainly, the 1-bit digital amplifier having the above-described configuration can reproduce the original sound more faithfully than an analog amplifier or a multi-bit digital amplifier, and can also reduce power consumption.
[0006]
However, in the conventional 1-bit digital amplifier, the noise level in the audible band (generally ˜20 [kHz]) is reduced by using the ΔΣ modulation method as shown in FIG. The noise suddenly increased in the high band (for example, 500 [kHz] to several [MHz]), which is the reception frequency band. In particular, when the order of the ΔΣ modulation method is increased in order to cope with high-fidelity audio directed to a high S / N in the audible band, the high-band noise is further increased. In addition, when the sampling frequency of the ΔΣ modulation method is increased in order to cope with high-fidelity audio in which a wide reproduction band (for example, ~ 100 [kHz]) is directed, as shown in FIG. As a result, the frequency moved to the high frequency side, and the high band noise was increased.
[0007]
Thus, when the noise level in the reception frequency band of the tuner increases, the high-band noise is radiated to the antenna of the tuner, the S / N of the reception frequency band is deteriorated, and there is a risk of causing problems such as a decrease in reception accuracy. there were. In particular, a conventional 1-bit digital amplifier is included in an audio reproduction apparatus (for example, see Patent Document 2) having an auto-tuning function (a function of automatically searching for a receivable channel signal by sweeping the frequency of a high-frequency signal obtained by an antenna) If it is mounted as it is, there is a possibility that the auto-tuning operation may be mistaken as a channel signal that can receive the high-band noise radiated to the antenna.
[0008]
In view of the above problems, an object of the present invention is to provide a digital amplifier capable of performing noise reduction in an optimum frequency band according to the situation, and an audio reproduction apparatus using the digital amplifier.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a digital amplifier according to the present invention includes a 1-bit conversion unit that converts an analog signal or a multi-bit digital signal into a 1-bit digital signal using a ΔΣ modulation method, and the 1-bit digital signal as power. An amplifier for amplifying and a digital / analog converter for analog-converting the amplified 1-bit digital signal, wherein the order of the ΔΣ modulation method , or the order and sampling frequency are: It is configured to be variably controlled according to a predetermined control signal. By adopting such a configuration, it is possible to perform noise reduction in an optimal frequency band according to the situation.
[0010]
An audio reproducing apparatus according to the present invention is an audio reproducing apparatus comprising: a tuner that detects a desired channel signal from an input signal; and a digital amplifier that digitally amplifies the detected channel signal. The amplifier uses a ΔΣ modulation method to convert the channel signal into a 1-bit digital signal, an amplifying unit for power-amplifying the 1-bit digital signal, and analog-converting the amplified 1-bit digital signal And the order of the ΔΣ modulation method , or the order and sampling frequency are variably controlled in accordance with a control signal from the tuner.
[0011]
Specifically, the control signal is a detection determination signal of the input signal, and the order of the ΔΣ modulation method , or the order and the sampling frequency are set to be high when the input signal is present. It is configured to be variably controlled according to the control signal so as to be low when there is no signal.
[0012]
More specifically, the tuner is a synthesizer having an auto-tuning function that automatically searches for a receivable channel signal by sweeping the frequency of the input signal in addition to the normal receiving function of the input signal. The order of the delta-sigma modulation method , or the order and sampling frequency are variably controlled in accordance with the control signal so as to be high during normal reception of the input signal and low during auto-tuning operation. It is said.
[0013]
By adopting such a configuration, in the digital amplifier, at the time of normal reception of the input signal, the order of the ΔΣ modulation system , or the order and the sampling frequency are increased to increase the S / N of the audible band and the reproduction band. Priority is given to wide area, and during auto-tuning operation, the order of ΔΣ modulation system , or the order and sampling frequency are lowered to give priority to improving the accuracy of auto-tuning operation (reducing noise in the reception frequency band). Accordingly, it is possible to perform noise reduction in an optimal frequency band.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an embodiment of an audio reproducing apparatus equipped with a 1-bit digital amplifier according to the present invention. As shown in the figure, the audio playback apparatus of the present embodiment includes a synthesizer 1, a volume controller 2, a 1-bit digital amplifier 3, and a control microcomputer 4.
[0015]
The synthesizer 1 includes an antenna 11, a high-frequency signal amplification circuit 12 (hereinafter referred to as an RF [Radio Frequency] circuit 12), an intermediate frequency signal conversion circuit 13 (hereinafter referred to as an IF [Intermediate Frequency] circuit 13), and detection. The circuit 14 and the tuning indicator 15 are provided, and a channel signal (analog audio signal in this embodiment) corresponding to the control signal of the control microcomputer 4 is detected from the RF signal obtained by the antenna 11, To the volume controller 2 of the stage. Further, the synthesizer 1 of the present embodiment has an auto-tuning function for automatically searching for a receivable channel signal by sweeping the frequency of the RF signal in addition to the normal reception function of the RF signal.
[0016]
In the synthesizer 1 configured as described above, the tuning detection signal output from the tuning detection terminal 13a of the IF circuit 13 is the RF signal detection determination signal, and the reception frequency band of the synthesizer 1 (for example, 500 [kHz]). If there is a signal input of a predetermined level or more in .about. [MHz]), it becomes a low level, and if not, it becomes a high level. The RF signal detection determination result based on the tuning detection signal is notified by the tuning indicator 15.
[0017]
The volume controller 2 analog-amplifies the desired channel signal detected by the synthesizer 1 and sends it to the 1-bit digital amplifier 3 at the subsequent stage.
[0018]
The 1-bit digital amplifier 3 includes a ΔΣ modulation 1-bit signal generation circuit 31 that converts the analog audio signal into a 1-bit digital audio signal using a ΔΣ modulation method, and an amplification circuit 32 that amplifies the power of the 1-bit digital audio signal. (Generally a bridge type power amplifier circuit), and a digital / analog converter circuit 33 (hereinafter referred to as a D / A [Digital / Analog] converter circuit 33) for analog-converting the amplified 1-bit digital audio signal; After the analog audio signal from the volume controller 2 is digitally amplified, it is sent again as an analog output to a load (speaker or the like) connected to the subsequent stage.
[0019]
Further, the 1-bit digital amplifier 3 of the present embodiment sets the order of the ΔΣ modulation method to a predetermined value (third or seventh order in this embodiment) as means for reducing noise in an optimum frequency band according to the situation. And the first and second order setting signal generators 34 and 35, and the sampling frequency of the ΔΣ modulation method is set to a predetermined value (in this embodiment, 32 [fs] or 64 [fs], 1 [fs] = 44. 1 [kHz]), and any one of the first and second order setting signal generators 34 and 35 based on the tuning detection signal from the synthesizer 1 The first relay 38, one of which is connected to the ΔΣ modulation 1-bit signal generation circuit 31, and the first and second sampling oscillators 36, 37 based on the tuning detection signal from the synthesizer 1 as well. Comprising a displacement or the other and the second relay 39 to be connected to the ΔΣ modulated 1-bit signal generation circuit 31, a.
[0020]
In the audio reproducing apparatus having the above configuration, when there is no signal input of a predetermined level or higher in the reception frequency band of the synthesizer 1 and the tuning detection signal is at the high level, the first and second relays 38 and 39 are of the first order. The setting signal generator 34 and the first sampling oscillator 36 are connected to the ΔΣ modulation 1-bit signal generation circuit 31, and the order of the ΔΣ modulation method and the sampling frequency are set to the lower one (third order, 32 [fs]). On the other hand, when a signal level of a predetermined level or more is input to the reception frequency band of the synthesizer 1 and the tuning detection signal is at a low level, the first and second relays 38 and 39 are connected to the second order setting signal generator 35 and the second order setting signal generator 35. The 2-sampling oscillator 37 is connected to the ΔΣ modulation 1-bit signal generation circuit 31, and the order and sampling frequency of the ΔΣ modulation method are set to the higher one (7th order, 64 [fs]).
[0021]
By performing such relay control, during normal reception of an RF signal (a state in which a signal input of a predetermined level or more is present in the reception frequency band of the synthesizer 1), the order of the ΔΣ modulation method and the sampling frequency are increased to an audible band. Priority is given to higher S / N and wider reproduction band, and during auto-tuning operation (when there is no signal input of a predetermined level or higher in the reception frequency band of synthesizer 1), the order and sampling frequency of the ΔΣ modulation method are set. It is possible to reduce the noise in the optimum frequency band according to the situation, such as lowering the priority and improving the accuracy of the auto-tuning operation (reducing the noise in the reception frequency band).
[0022]
In the above embodiment, the description has been given by taking as an example the configuration in which both the order of the ΔΣ modulation method and the sampling frequency are variably controlled. However, the configuration of the present invention is not limited to this, and either Only one of them may be variable control.
[0023]
Further, in the above embodiment, as a means for setting the order of the ΔΣ modulation method and the sampling frequency, a configuration in which two order setting signal generators and two sampling oscillators are provided has been described as an example. The configuration of the present invention is not limited to this, and the number thereof may be increased.
[0024]
【The invention's effect】
As described above, the digital amplifier according to the present invention and the audio reproduction apparatus using the digital amplifier can perform noise reduction in an optimum frequency band depending on the situation.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an audio reproducing apparatus equipped with a 1-bit digital amplifier according to the present invention.
FIG. 2 is a diagram illustrating conventional noise floor characteristics.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Synth tuner 11 Antenna 12 High frequency signal amplification circuit (RF circuit)
13 Intermediate frequency signal conversion circuit (IF circuit)
13a tuning detection terminal 14 detection circuit 15 tuning indicator 2 volume controller 3 1-bit digital amplifier 31 ΔΣ modulation 1-bit signal generation circuit 32 amplification circuit 33 digital / analog conversion circuit (D / A conversion circuit)
34 First order setting signal generator 35 Second order setting signal generator 36 First sampling oscillator 37 Second sampling oscillator 38 First relay 39 Second relay 4 Control microcomputer

Claims (2)

An audio reproduction apparatus comprising: a tuner that detects a desired channel signal from an input signal; and a digital amplifier that digitally amplifies the detected channel signal, wherein the digital amplifier uses the ΔΣ modulation method. A 1-bit converter for converting a channel signal into a 1-bit digital signal, an amplifier for power-amplifying the 1-bit digital signal, and a digital / analog converter for analog-converting the amplified 1-bit digital signal The order of the delta-sigma modulation method, or the order and the sampling frequency are made higher when the input signal is present, depending on the detection determination signal of the input signal inputted as a control signal from the tuner. , Eau characterized in that it is variably controlled so as to be lower when not the input signal Oh reproducing apparatus. The tuner is a synthesizer having an automatic tuning function for automatically searching for a receivable channel signal by sweeping the frequency of the input signal in addition to the normal receiving function of the input signal, and the order of the ΔΣ modulation method. The order and the sampling frequency are variably controlled according to the control signal so as to be high during normal reception of the input signal and low during auto-tuning operation. The audio playback device according to 1.

Images