JP3348036B2 - Digital switching amplifier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital switching amplifier which is suitably implemented for an audio signal and which can amplify the audio signal and the like with high efficiency.

[0002]

2. Description of the Related Art By sampling the analog sound signal at a frequency sufficiently higher than its effective frequency band, the signal is subjected to PWM (pulse width modulation) or ΔΣ modulation, and an obtained digital signal is supplied to a switching circuit. A switching circuit switches a predetermined constant voltage from a constant voltage source, and outputs the switching output to a load after performing analog conversion and harmonic removal by a low-pass filter, thereby power-amplifying the analog original signal. Switching amplifiers are conventionally used.

In this digital switching amplifier, a semiconductor power amplifier element in the switching circuit is used not in a linear region (unsaturated region) but in a non-linear region (saturated region) as in a conventional amplifier. Therefore, power amplification can be performed with extremely high efficiency.

[0004] In addition, a 1-bit signal obtained by Δ 音源 modulation, in particular, has an effective frequency band or a wide dynamic range by appropriately selecting coefficients of an integrator or an adder. It has an excellent feature that the frequency characteristics can be set according to the above. For this reason, CDs (compact discs) and DVDs
(Digital Video Discs)
With the adoption of bit signals, commercialization is about to begin. If the 1-bit signal obtained by the ΔΣ modulation is configured to be input to a digital switching amplifier and analog demodulated, all digital transmission is performed from the medium through the reproducing device to the amplifier, and high-fidelity sound is transmitted. Playback becomes possible.

[0005]

As described above, in the Δ あ る modulation, it is possible to arbitrarily set the frequency characteristics such as the effective frequency band and the dynamic range. However, if the characteristics of the low-pass filter deviate from the ΔΣ modulation characteristics, it is difficult to reproduce the sound with high fidelity.

For example, when the quantization noise distribution determined by the ΔΣ modulation algorithm has the characteristic indicated by reference numeral α1 in FIG. 5A, the cut-off frequency of the low-pass filter is set to 20 kHz. ] Is required. On the other hand, when the quantization noise distribution by the ΔΣ modulation algorithm has a characteristic indicated by reference numeral α2 in FIG. 5B, the cut-off frequency of the low-pass filter is set to 16 kHz. ] Is desired. Note that the quantization noise distribution indicated by the reference signs α1 and α2 is such that the input signal to the ΔΣ modulation circuit is 1
[KHz] sine wave and the input signal level is -60 [d
B].

On the other hand, the digital switching amplifier has the low-pass filter at the last stage, and the low-pass filter is constituted by, for example, a multi-stage LC or LRC integrator as shown in FIG. . If the LRC constant has an error of, for example, 1%, there is a problem in that a reproduced sound signal is audibly distorted.

Further, the user selects such a digital switching amplifier in consideration of a desired rated capacity and price, similarly to a normal audio amplifier. Similarly, a speaker which is a load also has a rated capacity. Make a selection in consideration of price and price. For this reason, even if the LRC constants of the low-pass filter are combined with high accuracy, there is a problem that the initial characteristics with high fidelity cannot be exhibited depending on the characteristics of the speakers to be combined.

For example, when a speaker having a designed impedance of 8 [Ω] is connected to a low-pass filter designed with a load impedance of 8 [Ω] by the speaker, as shown in FIG. 20 [k
Hz] can reproduce sound with a flat initial frequency characteristic up to the upper limit of the effective frequency band, but when a speaker having the impedance of 4 [Ω] is connected,
As shown in FIG. 7B, sound reproduction can be performed only with the characteristics in which the high-frequency side is reduced. Particularly, in the case of a multi-way speaker, the above problem is remarkable due to the influence of the network. Furthermore, there is a problem that not only the increase in noise perceived as described above but also the connection of a speaker having an impedance different from the design causes damage to the speaker and unnecessary radiation of high frequency.

It is an object of the present invention to provide a digital switching amplifier capable of performing high-fidelity power amplification in accordance with load characteristics.

[0011]

A digital switching amplifier according to the present invention converts an analog original signal into an input digital signal obtained by sampling the analog original signal at a frequency sufficiently higher than the effective frequency band of the analog original signal. In response, the switching circuit switches a predetermined constant voltage from the constant voltage source, outputs the switching output to a load after performing analog conversion and harmonic removal by a low-pass filter, and amplifies the analog original signal with high efficiency. In the digital switching amplifier, a plurality of low-pass filters are provided with different frequency characteristics from each other, and the low-pass filter responds to a cut-off frequency characteristic of a modulation circuit that modulates the analog original signal into an input digital signal to the digital switching amplifier. To select the frequency characteristic of the low-pass filter. Characterized in that it comprises a filter switching means.

According to the above arrangement, in a modulation circuit for modulating an analog original signal such as ΔΣ modulation into an input digital signal of the digital switching amplifier, for example,
The modulation circuit responds to a cut-off frequency characteristic determined by an algorithm such as a coefficient of an integrator or an adder, that is, a filter corresponding to the characteristic shown in FIG. 5A and FIG. The switching means selects a low-pass filter having a suitable frequency characteristic from among a plurality of types of low-pass filters.

Therefore, the analog original signal can be amplified not only with high efficiency but also with high fidelity and output to a load such as a speaker.

A digital switching amplifier according to a second aspect of the present invention responds to an input digital signal obtained by sampling an analog original signal at a frequency sufficiently higher than the effective frequency band of the analog original signal. A switching circuit switches a predetermined constant voltage from the constant voltage source, and outputs the switching output to a load after performing analog conversion and harmonic removal by a low-pass filter,
In a digital switching amplifier configured to amplify the power of the analog original signal with high efficiency, a plurality of types of the low-pass filters are provided with different frequency characteristics from each other, and in response to the frequency characteristics of the analog original signal, It is characterized by including filter switching means for selecting a frequency characteristic.

According to the above arrangement, when the analog original signal is an acoustic signal, for example, the filter switching means has the characteristic shown in FIG. 5 (a) and the characteristic shown in FIG. 5 (b). Next, the frequency characteristic of the low-pass filter that matches the frequency characteristic determined by the type of music or the type of musical instrument is selected.

Therefore, the analog original signal can be amplified with high fidelity as well as high efficiency and output to a load such as a speaker.

Still further, the digital switching amplifier according to the third aspect of the present invention responds to an input digital signal obtained by sampling an analog original signal at a frequency sufficiently higher than the effective frequency band of the analog original signal. A switching circuit switches a predetermined constant voltage from a constant voltage source, and outputs the switching output to a load after performing analog conversion and harmonic removal by a low-pass filter, and power-amplifies the analog original signal with high efficiency. In the digital switching amplifier described above, a plurality of types of the low-pass filters are provided with different frequency characteristics from each other, and filter switching means for selecting the frequency characteristics of the low-pass filter in response to the impedance of the load is included.

According to the above arrangement, the filter switching means combines these speakers and the low-pass filter in accordance with the impedance of the load, for example, the impedance of the speakers when the analog original signal is an acoustic signal. To make the analog demodulation characteristics the initial characteristics,
Switch the low pass filter.

Therefore, the analog original signal can be amplified not only with high efficiency but also with high fidelity and output to a load such as a speaker.

According to a fourth aspect of the present invention, there is provided a digital switching amplifier, comprising: voltage detecting means for detecting a voltage applied to a load terminal; current detecting means for detecting a load current;
And a measuring means for measuring an impedance of the load in response to detection results of the voltage detecting means and the current detecting means.

According to the above configuration, the impedance of the load is automatically measured from the voltage and the load current at the load end, so that the work of switching the filter characteristics corresponding to the impedance of the load can be eliminated.

Therefore, the initial characteristics can be exhibited between any combination of the switching amplifier and the load even when used by not only some specialized users but also general users.

Still further, in the digital switching amplifier according to the present invention, the analog original signal is an acoustic signal, the load is a speaker, and the input digital signal is obtained by ΔΣ-modulating the analog original signal. Characterized by a low bit signal.

According to the above arrangement, in the sound reproducing apparatus,
The user selects a product in consideration of the desired rated output, price, etc. In order to adapt to this, even if multiple types of products are lined up for each of the switching amplifier and the speaker, Initial characteristics can be exhibited between the combinations. In particular, claim 4
In the case of, since the measuring means automatically measures the impedance of the speaker and selects the filter characteristic, not only some specialized users, but also widely used by general users,
Initial characteristics can be exhibited.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
It is as follows if it demonstrates based on FIGS. 1-4 and FIG.

FIG. 1 is a block diagram showing an electrical configuration of a digital switching amplifier 1 according to one embodiment of the present invention. The 1-bit signal source 2 converts the analog audio signal into ΔΣ
By modulating or reproducing a medium on which a 1-bit sound signal is recorded, 1-bit signals “+1” and “−1” are created,
Input to the digital switching amplifier 1. The digital switching amplifier 1 generally includes a constant voltage switch 3
, A low-pass filter 4, a voltage detector 5, a current detector 6, and an impedance measurement circuit 7.

The constant voltage switch 3 switches predetermined constant voltages + E ₀ and −E ₀ from a constant voltage source (not shown) in response to the input 1-bit signals “+1” and “−1”. The obtained large-amplitude pulse signal is demodulated into an analog sound signal in the low-pass filter 4, and
The signal is output after the harmonic components due to the switching are removed, and is acoustically generated by the speaker 8 as a load.

It should be noted that in the present invention, a plurality of filter circuits F11, F12,
..., F1m; F21, F22, ..., F2i; Fn1, F
n2,..., Fnj (hereinafter collectively referred to by reference numeral F). The filter circuit F is
The group is divided into a plurality of groups F1, F2,..., Fn. These groups F1 to Fn are selected according to the impedance of the speaker 8 to be connected, as described later. Then, in each of the groups F1 to Fn,
Furthermore, a plurality of filter circuits F11, F12,
..., F1m; F21, F22, ..., F2i; Fn1, F
, Fnj are provided. For this reason, switches S11 and S12; S21 and S22 (hereinafter, collectively referred to as S) are provided in the low-pass filter 4 for selecting those filter circuits F.

For the switching of the switch S, first, the group setting is performed by the impedance measuring circuit 7. The voltage at the load terminal to which the speaker 8 is connected is detected by the voltage detector 5, and the load current to the speaker 8 is detected by the current detector 6. The impedance measurement circuit 7 responds to these detection results,
The groups F1 to Fn are switched.

FIG. 2 is a block diagram showing a specific configuration of the impedance measuring circuit 7.

The load terminal voltage signal ↑ from the voltage detector 5
E (↑ represents a vector; the same applies hereinafter) and a load current signal ΔI from the current detector 6,
The transfer function measuring unit 11 measures the transfer function H (x) from the following equation.

↑ I = H (x) · ↑ E (1) The transfer function H (x) obtained as shown by the above equation (1)
In, the extraction unit 12 extracts the transfer function H (fc) at the cutoff frequency fc of the filter circuit F used for measurement, and from the extraction result, the impedance conversion unit 13 calculates
The impedance of the speaker 8 at the cutoff frequency fc is determined. The group switching control unit 14 outputs impedance information for selecting the groups F1 to Fn in the low-pass filter 4 according to the impedance thus obtained.

The low-pass filter 4 is, for example, as shown in FIG.
, For example, the sampling frequency of the 1-bit signal “+1” and “−1” is set to 2.8.
[MHz], and the cut-off frequency fc is 22 [kHz].
And the impedance of the speakers 8 is 8
Table 1 shows an example of selecting constants of the filter circuit F when [Ω], 6 [Ω], and 4 [Ω] are set.

[0034]

[Table 1]

In the present invention, the cut-off frequency information and the input source information are given to the low-pass filter 4 from the 1-bit signal source 2. The cutoff frequency information indicates cutoff frequency characteristics of a ΔΣ modulation circuit in the 1-bit signal source 2 and a modulation circuit used for ΔΣ modulation when recording a 1-bit signal on the medium. It is determined by an algorithm such as a coefficient of a multiplier or a multiplier. In response to the cutoff frequency information, a detailed selection of the filter circuit F in each of the groups F1 to Fn is performed. For example, the characteristic shown in FIG.
The characteristics of the low-pass filter 4 can be switched according to the characteristics shown in FIG.

The input source information represents, for example, the type of music such as jazz and classical music, and the musical instrument being used, and also represents frequency characteristics in the same manner as the cutoff frequency information.

The switching of the filter circuit F in the low-pass filter 4 may be performed by using any one or any two of the impedance information, the cutoff frequency information, and the input source information. Corresponding to the impedance of the loudspeaker 8 is particularly advantageous in that it suppresses audible noise and also suppresses the above-described damage to the loudspeaker 8 and unnecessary radiation of high frequencies.

Further, the detection of the impedance of the speaker 8 may be performed not by the automatic detection as described above but by a user setting using a switch or the like. However, the automatic detection as described above is advantageous because the initial characteristics can be exhibited even if a user who does not have the specialized knowledge to purchase a popular price machine uses it. In this case, the measurement of the impedance may be performed in response to detection of power-on, connection of the speaker 8, or the like, or may be performed periodically. When the power is turned on or connection is detected, the 1-bit signal [+1] from the 1-bit signal source 2 may not be input in some cases. Therefore, a configuration is provided in which a dummy signal is input to the constant voltage switch 3. You may.

FIG. 3 is an electric circuit diagram showing a configuration example of the constant voltage switch 3. As shown in FIG. The constant-voltage switch 3 between the power supply and the low voltage -E ₀ of the high voltage + E _0, a series circuit of semiconductor switching elements Q11, Q12, the mutual series circuit of the semiconductor switching devices Q13, Q14 They are arranged in parallel. A connection point between the semiconductor switching elements Q11 and Q12 is connected to one output terminal P2.
The connection point between the semiconductor switching elements Q13 and Q14 becomes the other output terminal P22.

The 1-bit signal "+1" is supplied to the control input terminal P11 of the semiconductor switching element Q11, and the control input terminal P1 of the semiconductor switching element Q12 is
2 is supplied with an inverted signal of the 1-bit signal “+1”. The 1-bit signal “−1” is applied to the control input terminal P13 of the semiconductor switching element Q13, and the control input terminal P1 of the semiconductor switching element Q14 is controlled.
4 is provided with an inverted signal of the 1-bit signal “−1”.

FIG. 4 shows operation waveforms of the constant voltage switch 3. As is clear from FIG. 4, the output terminals P21, P2
Between the two, not only the voltage of + E ₀ or -E ₀ is applied, but also a ternary ΔΣ modulation output having a 0 voltage application timing at which both output terminals P21 and P22 are short-circuited. In this way, the period during which the 0 voltage is applied becomes longer at the time of a small signal, and power efficiency can be improved.
It is needless to say that the constant voltage switch 3 is not limited to the configuration shown in FIGS. 3 and 4 and may have another configuration. Also, the input digital signal to the digital switching amplifier 1 is not limited to the three-valued ΔΣ modulated signal,
ΣIt may be a modulation signal or a PWM signal.

As described above, in the digital switching amplifier 1 according to the present invention, the low-pass filter 4 is constituted by the plurality of filter circuits F having different frequency characteristics, and firstly, the low-pass filter 4 corresponds to the impedance information representing the impedance of the speaker 8. , These speakers 8 and the low-pass filter 4
Are selected so that the analog demodulation characteristics obtained by combining the above-mentioned characteristics with the initial characteristics are selected, and furthermore, the cut-off frequency information and the music which indicate the cut-off frequency characteristics determined by the algorithm of the ΔΣ modulation circuit and the like. In response to input source information indicating the type of
Since the optimum filter circuit F is selected in the groups F1 to Fn, not only the analog original signal can be obtained with high efficiency,
The power can be amplified with high fidelity and output to the speaker 8. Further, it is also possible to suppress breakage of the speaker 8 and unnecessary radiation of high frequency.

Since the impedance measuring circuit 7 automatically measures the impedance of the speaker 8,
Even if a plurality of types of products having different rated outputs and prices are lined up, not only some specialized users but also a wide range of general users can use any combination of the digital switching amplifier 1 and the speaker 8. Thus, the initial characteristics can be exhibited.

[0044]

As described above, the digital switching amplifier according to the first aspect of the present invention switches a predetermined constant voltage in response to an input digital signal obtained by sampling an analog original signal, and outputs its switching output. In a digital switching amplifier that outputs an analog original signal such as ΔΣ modulation to an input digital signal of the digital switching amplifier in response to a cutoff frequency characteristic of a modulation circuit. Of the low-pass filters of which the frequency characteristics are adapted.

Therefore, the analog original signal can be amplified not only with high efficiency but also with high fidelity and output to a load such as a speaker.

The digital switching amplifier according to the second aspect of the present invention switches a predetermined constant voltage in response to an input digital signal obtained by sampling an analog original signal, and outputs a switching output thereof. Output to a load via a low-pass filter in response to the frequency characteristics of the analog original signal determined by the type of music and the type of musical instrument Select the one with the appropriate characteristics.

Therefore, the analog original signal can be amplified not only with high efficiency but also with high fidelity and output to a load such as a speaker.

Furthermore, the digital switching amplifier according to the third aspect of the present invention switches a predetermined constant voltage in response to an input digital signal obtained by sampling an analog original signal, and performs the switching. In a digital switching amplifier in which an output is output to a load via a low-pass filter, an analog demodulation characteristic combining these loads and the low-pass filter becomes an initial characteristic corresponding to the impedance of a load such as a speaker. Then, among the plurality of types of low-pass filters, a filter having a suitable frequency characteristic is selected.

Therefore, the analog original signal can be amplified not only with high efficiency but also with high fidelity and output to a load such as a speaker.

The digital switching amplifier according to the fourth aspect of the present invention automatically measures the load impedance from the load terminal voltage and the load current as described above.

Therefore, the switching operation of the filter characteristic corresponding to the impedance of the load can be eliminated, so that not only some specialized users but also general users can use the switching amplifier and the load. , The initial characteristics can be exhibited.

In the digital switching amplifier according to the present invention, the analog original signal is used as an audio signal, the load is used as a speaker, and the input digital signal is converted into a low bit signal by Δ に よ る modulation. I do.

Therefore, in the sound reproducing apparatus, a user selects a product in consideration of a desired rated output, a price, and the like. In order to adapt to this, a plurality of types of products are provided for each of the switching amplifier and the speaker. , The initial characteristics can be exhibited between any combination of products. In particular, in the case of claim 4, since the measuring means automatically measures the impedance of the speaker and selects the filter characteristic, not only some specialized users, but also widely used by general users, Initial characteristics can be exhibited.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an electrical configuration of a digital switching amplifier according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration example of an impedance measuring circuit in the digital switching amplifier illustrated in FIG.

FIG. 3 is an electric circuit diagram showing a configuration example of a constant voltage switch used in the digital switching amplifier.

FIG. 4 is a waveform chart for explaining the operation of the constant voltage switch shown in FIG.

FIG. 5 is a graph showing a change in a frequency characteristic due to a change in an algorithm of a ΔΣ modulation signal that is one input signal of a digital switching amplifier.

FIG. 6 is an electric circuit diagram showing a configuration example of a low-pass filter used in a digital switching amplifier.

FIG. 7 is a graph showing a change in frequency characteristics due to a speaker impedance shift in a digital switching amplifier according to the related art.

[Explanation of symbols]

Reference Signs List 1 digital switching amplifier 2 1-bit signal source 3 constant voltage switch (switching circuit) 4 low-pass filter 5 voltage detector (voltage detecting means) 6 current detector (current detecting means) 7 impedance measuring circuit (measuring means) 8 speaker (load) 11) Transfer function measuring unit 12 Extracting unit 13 Impedance converting unit 14 Group switching control unit F11, F12, ..., F1m; F21, F22, ..., F
2i; Fn1, Fn2,..., Fnj Filter circuit F1 to Fn group S11, S12; S21, S22 Switch (filter switching means)

Claims (5)

(57) [Claims] A switching circuit responds to an input digital signal obtained by sampling an analog original signal at a frequency sufficiently higher than an effective frequency band of the analog original signal. In a digital switching amplifier, the switching output of which is analog-converted and harmonic-removed by a low-pass filter and output to a load to amplify the analog original signal with high efficiency, the low-pass filters are connected to each other. A plurality of types having different frequency characteristics, and filter switching means for selecting a frequency characteristic of the low-pass filter in response to a cut-off frequency characteristic of a modulation circuit for modulating the analog original signal into an input digital signal to the digital switching amplifier. Digital switching amplifier characterized by the following: 2. A switching circuit according to claim 1, wherein said switching circuit responds to an input digital signal obtained by sampling said analog original signal at a frequency sufficiently higher than an effective frequency band of said analog original signal. In a digital switching amplifier, the switching output of which is analog-converted and harmonic-removed by a low-pass filter and output to a load to amplify the analog original signal with high efficiency, the low-pass filters are connected to each other. A digital switching amplifier comprising a plurality of types having different frequency characteristics, and a filter switching means for selecting a frequency characteristic of the low-pass filter in response to a frequency characteristic of the analog original signal. 3. A switching circuit in response to an input digital signal obtained by sampling an analog original signal at a frequency sufficiently higher than an effective frequency band of the analog original signal. In a digital switching amplifier, the switching output of which is analog-converted and harmonic-removed by a low-pass filter and output to a load to amplify the analog original signal with high efficiency, the low-pass filters are connected to each other. A digital switching amplifier comprising a plurality of types provided with different frequency characteristics, and a filter switching means for selecting a frequency characteristic of the low-pass filter in response to an impedance of the load. 4. A voltage detecting means for detecting a voltage applied to a load terminal, a current detecting means for detecting a load current, and an impedance of the load in response to detection results of the voltage detecting means and the current detecting means. 4. The digital switching amplifier according to claim 3, further comprising a measuring unit for measuring. 5. The analog original signal is an audio signal, the load is a speaker, and the input digital signal is a low bit signal obtained by ΔΣ modulating the analog original signal. Item 5. A digital switching amplifier according to any one of Items 1 to 4.