JP2000223965A - Audio amplifier circuit and audio device using the same circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption and to highly efficiently extend a battery operation time by providing a drive current generation circuit which receives the pulse of a pulse generation circuit and generates a current with a current value corresponding to PWM modulation, etc., and driving a speaker in accordance with the output of the drive current generation circuit. SOLUTION: A D/A conversion circuit (D/A) 4 receives the digital value of a bit shifter 3 from its output terminal 3c and converts it into an analog signal. The analog signal output of the D/A 4 is inputted to a PWM switching power amplifier 5. The amplifier 5 consists of a PWM pulse generation circuit 5a and a pulse oscillator 5b oscillating in 500 kHz pulses. Furthermore, the output pulses from the oscillator 5b are transmitted to an L-type filter circuit 6. The circuit 6 converts a PWM signal into a drive current having a current value corresponding to the amplitude of the analog signal by using the coil L, the signal converted into the drive current is applied to a speaker 7 and converted into sound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal amplifying circuit and an audio apparatus using the same, and more particularly, to a portable magnetic tape player or a portable CD player for converting a digital audio signal into an analog audio signal and amplifying the same. 2. Description of the Related Art In an audio amplifier circuit of an audio device such as an audio player using an IC memory (IC memory audio player), a portable audio device capable of reducing the power consumption of the circuit and increasing the performance time of a battery with high efficiency. About.

[0002]

2. Description of the Related Art Conventional headphone stereo, DCC,
Portable magnetic tape players such as DAT, MD, C
Audio devices such as portable disk players such as D and currently developed IC memory audio players are driven by dry batteries, and the number is about one or two. Therefore, the power supply voltage of the audio circuit is
It is only about 1.2V or 2.4V. In addition, in many cases, a stereo function is provided, and the output amplifier circuit has two systems. In such portable audio equipment, there are many demands for using a single battery as a drive power source, and there is a strong demand for realizing a long-time performance. Furthermore, recent circuits are equipped with a low-frequency boost amplifier, and the power consumption tends to increase.

[0003] In this kind of circuit or device, the power consumption is large in an audio output circuit and a motor drive circuit. Japanese Patent Application Laid-Open No. HEI 4-111506 and Japanese Patent Application No. Hei.
No. 50637 and the like. The former applies an input signal to a power supply system separate from the signal amplification system, performs full-wave rectification on the input signal, and controls the operating current of the audio output circuit by the full-wave rectified signal to respond to the amplitude of the input signal. Power supplied to the audio output circuit. In the latter case, when a stereo signal is amplified, the center amplifier portion of the virtual ground is replaced with a switching regulator to generate a voltage at a virtual ground level, thereby reducing power consumption. 2. Description of the Related Art A conventional audio amplifier circuit of this type, particularly a CD or MD, an IC memory audio player, etc., converts a digital signal into an analog signal, amplifies the analog signal, and drives a dynamic speaker by outputting the analog signal. In a portable magnetic tape player or the like, a signal reproduced in analog is analog-amplified and a speaker is driven by an analog signal output.

[0004]

In the case of the amplification of an analog signal and the driving of a dynamic speaker by the output of an analog signal, a preamplifier and a volume control circuit are required from a minute signal to a power output. Must be repeated many times. Therefore, the number of capacitors and resistance circuits increases, the number of transistors also increases, and the power conversion efficiency until sound is generated is at most about 60% to 70%. At present no further efficiency can be expected. Therefore,
The power consumption by the battery can be reduced only to a certain extent, and even if the circuit is reduced by using an IC, there is a limit to the reduction in thickness and size of the device. SUMMARY OF THE INVENTION An object of the present invention is to solve such problems of the prior art, and to provide an audio signal amplifying circuit and an audio device capable of reducing power consumption and extending the playing time of a battery with high efficiency. It is in.

[0005]

SUMMARY OF THE INVENTION An audio signal amplifying circuit and an audio device according to the present invention for achieving the above object are characterized by receiving a digital audio signal and responding to a digital control signal for adjusting a volume. An arithmetic circuit for generating a digital calculated value corresponding to volume adjustment, a D / A converting circuit for D / A converting the calculated value of the arithmetic circuit to generate an analog value, and an output value of the D / A converting circuit A pulse generating circuit for generating a pulse of a predetermined frequency whose generation period is PWM-modulated in accordance with the following, and a driving current generating circuit for receiving a pulse of the pulse generating circuit and generating a current having a current value corresponding to the PWM modulation And drives the speaker in accordance with the output of the drive current generation circuit.

[0006]

As described above, according to the present invention, since the circuit from volume control to audio output is constituted by the arithmetic circuit, the D / A conversion circuit, the pulse generation circuit, and the drive current generation circuit, the circuit until the generation of the drive signal It is not necessary to provide a large number of capacitors and resistor circuits in the circuit. In particular, since the output amplifier is a pulse generation circuit and the output for driving the speaker is based on the drive current generation circuit receiving the output of the pulse generation circuit, it is not necessary to amplify and output the analog signal.
The number of transistors can be reduced. In addition, since the volume can be directly adjusted by a digital value, the volume adjustment circuit becomes simpler than the case of an analog signal. As a result, the power conversion efficiency until the sound is generated is improved as compared with the case of the amplified output of the analog signal, and a small and thin device can be realized. In particular, it is possible to realize an audio device suitable for an IC memory audio player.

[0007]

FIG. 1 shows an audio signal output circuit 1 of an R-channel headphone amplifier. Since the L channel is a similar circuit, only the R channel is specifically shown, and the audio signal output circuit of the L channel is simply shown as a black box 2. Hereinafter, only the R channel audio signal output circuit 1 will be described, and the description of the L channel audio signal output circuit 2 will be omitted.
Reference numeral 10 denotes a controller, which is a circuit that generates a control signal as a digital value in order to adjust the volume and the like of the audio signal output circuits 1 and 2. Further, it generates a clock signal CLK. In the figure, a battery serving as a power supply is omitted. The R-channel audio signal output circuit 1 includes a bit shifter 3, a D / A conversion circuit (D / A) 4, a PWM switching power amplifier 5, and an L-type filter circuit 6 as a drive current generation circuit. The speaker 7 (right side) is driven.

The bit shifter 3 is a so-called shift register, and is a power-of-two multiplication circuit. This corresponds to a circuit for controlling the volume or the like in an analog signal amplifier circuit, corresponds to a volume control circuit for adjusting the volume in accordance with a volume control operation, and corresponds to an audio digital signal (IC) stored in the IC memory 9. The main signal S) is directly received at the input terminal 3a. The main signal S (audio digital signal) has 8 bits as valid bits, and n + 8 bits obtained by adding 1 bit indicating positive / negative to the reference level and n dummy bits of “0”, where n is 2 or more. It is an integer. In this embodiment, n = 7, and 7 bits are added to the higher order of 8 bits of the main signal, and 15 bits + 1 indicating positive / negative
It is a signal of 16 bits in total. This is read from the IC memory 9 by the controller 10. The input terminal 3b of the bit shifter 3 receives a 3-bit volume control signal Vd from the controller 10 according to the volume adjustment operation. The bit shifter 3 converts the 8-bit main signal S of the input terminal 3a accordingly to the digital value of the 3-bit volume control signal Vd received at the input terminal 3b.
Bit shift to upper bits. This bit shift is performed by adding a lower-order bit of "0", and a shifted signal is generated at the output terminal 3c. Note that the volume adjustment is “0”
In the state where the volume is not adjusted, no shift is performed.

More specifically, the bit shifter 3 comprises a 15-bit shift register 31 and a flip-flop (F / F).
32, a register 33, and a shift clock generation circuit 34. Controller 10 generates read signal R for memory 9 and supplies 16 bits of the read signal corresponding to the read signal R to input terminal 3 a of bit shifter 3. The shift clock generation circuit 34 of the bit shifter 3
The read signal R is received as a timing signal from the controller 10 to generate a control signal CT. In response to the control signal CT, 8 bits of the main signal S and 15 bits including a dummy bit are set in the shift register 31, and 1 indicating positive or negative
The bit is set in the flip-flop 32. Next, the shift clock generation circuit 33 converts the eight bits of the main signal S set in the shift register 31 and the dummy bits into a control signal CK in accordance with the clock CLK from the controller 10.
To shift in the upper digit direction by the digital value of the volume control signal Vd.

For example, if the 8-bit value of the main signal S is "10
010010 ", and assuming that the digital value of the volume control signal Vd is" 011 "(= 3), the main signal S is shifted upward by 3 bits. The value “011” is received at the input terminal 3b and the controller 10
From the control signal CK for three clocks
And shifts the data upward by adding 3 bits of “0” to the lower part of the set data “10010010”. As a result, “0” of the upper dummy bit overflows by 3 bits and disappears. As a result, the digital value of the main signal S becomes “1”.
The value of the shift register 31 becomes “00001001001000”.
This is 15 bits of 0 ".

When the shift by the shift clock generation circuit 34 is completed, a latch pulse Lp is generated from the shift clock generation circuit 34, as shown in FIG. A total of 16 bits including one bit of 3b (as the most significant bit) are set in the register 33 in parallel. Then, at the falling edge of the latch pulse Lp, the register 33 outputs 16-bit data (1 bit indicating positive or negative set in the flip-flop 32 and the shift register 31).
Is output in parallel to the D / A 4. At this time, one positive / negative bit is output as the most significant bit (MSB) as input.

In this case, since the value of the main signal S is doubled by one-bit shift, the value of the main signal S becomes eight times by the shift of three bits. Here, since the volume control signal Vd is 3 bits, the maximum shift amount is “111”.
(= 7), which is 128 times. Here, the output terminal 3c
Is 16 bits, and one bit is taken as the positive / negative sign, the effective bits are 15 bits, and the maximum shift is possible up to 7 bits. It should be noted that adding one sign bit plus or minus the reference level as an input signal to the main signal S on the input side makes the main signal S 9 bits. Therefore, the maximum multiple of the main signal S is 128
The output signal can be obtained up to 128 times.
However, this is for the amplitude of the signal, and the sound volume itself is in decibels, so that the sound is not output as 128 times.

The D / A 4 receives such a digital value of the bit shifter 3 from its output terminal 3c and converts it into an analog signal. Therefore, the output signal can be adjusted by a power of 2 by the bit shift by the bit shifter 3, and the volume at the time of output can be easily adjusted by a digital value. The analog signal output of the D / A 4 is input to the PWM switching power amplifier 5. The switching power amplifier 5 includes a PWM pulse generation circuit 5a and a pulse oscillator 5b oscillating with a pulse of 500 kHz as a switching power circuit. The switching power amplifier 5 has a predetermined frequency whose generation period is PWM-modulated according to the output value of the D / A 4, Here, this is a push-pull output pulse generation circuit capable of generating a 500 kHz pulse in both the positive side and the negative side with respect to the reference voltage. The predetermined frequency is preferably in the range of about 100 kHz to 1 MHz.

The PWM pulse generating circuit 5a includes, for example, a triangular wave generating circuit provided for each of the positive side and the negative side, and a comparator for comparing the output of the triangular wave generating circuit with an input signal. A4 output signal (FIG. 2
(A) D / A output) is received as an input signal, and the positive and negative amplitude levels are compared by respective comparators corresponding to the positive and negative signal levels. Generate a pulse whose pulse width increases. In the above case, the frequency of the triangular wave generation circuit is about 50 kHz, which is a sufficiently high frequency for the audio signal. The comparator on the positive side receives the input signal on the (+) input side, receives the triangular wave output on the (−) input on the reference side, and the comparator on the negative side receives the input signal on the (−) input side, +) Receives triangular wave output at input.

As a result, positive and negative PWM pulses are generated with respect to a predetermined reference level (refer to FIG. 2B). The positive and negative PWM signals are output from the PWM pulse generation circuit 5a.
The pulse generator 5b receives the M pulse,
b generates a switching pulse of 500 kHz for a certain period of the pulse, generates a positive pulse in accordance with the positive analog signal as the switching pulse, and generates a negative pulse in accordance with the negative analog signal. As a result, the pulse generation period is set to PW in accordance with the analog signal output of D / A4.
An M-modulated output pulse of 500 kHz (see FIG. 2C) is obtained from the pulse generator 5b. This output pulse is sent to the L-type filter circuit 6. Although the actual number of output pulses is larger than that shown in FIG. 2 (c), it is simplified and shown in FIG. 2 (c) for convenience of explanation. The L-type filter circuit 6 is an L-type filter in which a capacitor C is provided at the rear end of the coil L, and is grounded through the capacitor C. It is converted to the drive current that it has. The signal converted into the drive current is applied to the speaker 7, converted into sound, and output to the outside.

The L-type filter circuit 6 has a frequency of 5
Since a signal of 00 kHz is converted into a signal of an audio frequency, a passive circuit having a small coil and a small capacitor is sufficient. At this time, the coil component of the speaker 7 also contributes to the current value conversion. In such a circuit, there is no output amplifying circuit and the volume can be adjusted by digital values, so that the entire circuit from the volume adjusting circuit to the audio output amplifier is a simple circuit.

In the embodiment, the most significant bit (M
SB) as positive and negative sign bits, and the bit shifter stores the most significant bit in a flip-flop,
The bit of the main signal S is bit-shifted by one shift register in accordance with the volume. In this case, the flip-flop is deleted, and the shift register is shifted in accordance with each of the positive side and the negative side. The shift register may be provided in accordance with the sign bit of the positive or negative sign. In such a case, one most significant bit of the selected shift register should always be "1", and the other most significant bit should always be "0".

Further, in the embodiment, the bit shifter is used for volume control, but this is used for simplifying the circuit configuration. Instead of the bit shifter, a digital multiplier or a specific numerical value is used. Of course, the value of the main signal S may be calculated by calculating with the control value by a volume control circuit having a calculation circuit for multiplying or adding. The L-type passive filter circuit may be a circuit having a coil, and may be another circuit having a coil component. If the coil component of the speaker has a large L component, it can be used as it is. Further, a 1-bit positive / negative control code is added to the 3-bit volume control signal Vd of the embodiment, and the main signal S is shifted downward to adjust the volume.
Can be reduced to a power. As a result, the volume can be set to “0” or reduced. Such a volume control signal Vd may be 2 bits, or may be 3 bits or more.

[0019]

As described above, according to the present invention, since the circuit from volume control to audio output is constituted by the arithmetic circuit, the D / A conversion circuit, the pulse generation circuit and the drive current generation circuit, There is no need to provide a large number of capacitors and resistor circuits in the circuit up to the signal generation. In particular, since the output amplifier is a pulse generation circuit, and the output for driving the speaker depends on the drive current generation circuit receiving the output of the pulse generation circuit, it is not necessary to amplify and output the analog signal, and the number of transistors Can also be reduced. In addition, since the volume can be directly adjusted by a digital value, the volume adjustment circuit becomes simpler than the case of an analog signal. As a result, the power conversion efficiency until the sound is generated is improved as compared with the case of the amplified output of the analog signal, and a small and thin device can be realized. In particular, it is possible to realize an audio device suitable for an IC memory audio player.

[Brief description of the drawings]

FIG. 1 is a block diagram mainly showing a battery-driven audio output circuit according to an embodiment to which an audio signal amplifying circuit of the present invention is applied;

FIG. 2 is an explanatory diagram of operation waveforms of a PWM switching power amplifier.

[Explanation of symbols]

1, 2, audio signal output circuit, 3 bit shift,
4 ... D / A conversion circuit (D / A), 5 ... PWM switching power output amplifier, 5a ... PWM pulse generation circuit, 5
b: pulse oscillator, 6: L-type filter circuit, 7: headphone speaker, 10: controller, 3a, 3B: input terminal, 3c: output terminal, 31: shift register, 32
... Flip-flop (F / F), 33 ... Register, 34
... Shift clock generation circuit.

Claims (7)

[Claims] 1. An audio amplifier circuit for converting a digital audio signal into an analog audio signal and amplifying the digital audio signal, the digital amplifier corresponding to the digital audio signal in response to a digital control signal for adjusting the volume. An arithmetic circuit for generating a calculated value, a D / A conversion circuit for D / A converting the calculated value of the arithmetic circuit to generate an analog value, and a generation period corresponding to an output value of the D / A conversion circuit. A pulse generation circuit for generating a pulse of a predetermined frequency subjected to PWM modulation, and a drive current generation circuit for receiving the pulse of the pulse generation circuit and generating a current having a current value corresponding to the PWM modulation; An audio amplifier circuit that drives a speaker according to the output of the circuit. 2. The driving circuit according to claim 1, wherein the arithmetic circuit is a multiplying circuit, the driving current generating circuit is a filter circuit having a coil, and the pulse generating circuit has a period during which the switching is performed.
2. The audio amplifier circuit according to claim 1, wherein the switching power circuit becomes longer as the output values on the positive and negative sides of the / A conversion circuit become larger. 3. The multiplying circuit is a bit shifter, wherein the digital audio signal is read from an IC memory, and the number of data read from the IC memory is n (n is 2 or The bit shifter has a shift register, sets the digital audio signal to which the n dummy bits are added in the shift register, and sets the digital audio signal for the volume adjustment. 3. The audio amplifying circuit according to claim 2, wherein the data in the shift register is shifted in a direction of an upper digit in accordance with a digital control signal. 4. The digital audio signal, wherein the most significant bit is a sign bit indicating whether the value is positive or negative, and this sign bit is not shifted and is used as the most significant bit as the D bit.
5. The audio amplifier circuit according to claim 4, wherein the signal is output to a / A circuit. 5. An audio device for converting a digital audio signal into an analog audio signal and amplifying the same,
An arithmetic circuit that receives the digital audio signal and generates a digital calculation value corresponding to the volume adjustment in response to a digital control signal for adjusting the volume; and performs D / A conversion on the calculation value of the arithmetic circuit. D / to generate an analog value
An A conversion circuit, a pulse generation circuit for generating a pulse of a predetermined frequency whose generation period is PWM-modulated in accordance with the output value of the D / A conversion circuit, and receiving the pulse of the pulse generation circuit, corresponding to the PWM modulation An audio amplifier circuit having a drive current generation circuit that generates a current having a current value to be controlled, a controller that generates the control signal in accordance with a volume adjustment operation, and a speaker that is driven in accordance with an output of the drive current generation circuit. Audio device equipped with. 6. The driving circuit according to claim 1, wherein the arithmetic circuit is a multiplying circuit, the driving current generating circuit is a filter circuit having a coil, and the pulse generating circuit has a period during which the D is switched.
6. The audio apparatus according to claim 5, wherein the switching power circuit becomes longer as the output values on the positive and negative sides of the / A conversion circuit increase. 7. The multiplying circuit is a bit shifter, wherein the digital audio signal is read from an IC memory, and the number of data read from the IC memory is n (n is 2 or more) in an upper digit side. The bit shifter has a shift register, sets the digital audio signal to which the n dummy bits are added in the shift register, and sets the digital audio signal for the volume adjustment. 9. The audio device according to claim 8, wherein the data in the shift register is shifted in an upper digit direction in accordance with a digital control signal for the shift operation.