JPH04167623A - Output adjusting device - Google Patents

Abstract

PURPOSE:To perform the processing of the maximum amplification operation, etc., in accordance with a source voltage by adjusting the dynamic range of an analog signal outputted from a digital/analog converter by varying a reference voltage corresponding to the source voltage. CONSTITUTION:A means which varies the reference voltage of the digital/ analog converter 1 when the voltage value of power source is switched between, for example, an AC adapter and a battery is provided. For example, a device is comprised of a source voltage detecting means 2 for a comparator which detects the voltage value of the power source, etc., and a reference voltage switching means 3 consisting of a transistor which switches the reference voltage corresponding to the detection result of the source voltage detecting means 2 and a diode, etc. Switching is performed so as to increase the reference voltage when the source voltage is high, and to decrease the reference voltage when the source voltage is low. In such a way, it is possible to obtain the analog signal provided with the dynamic range fully corresponding to the source voltage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides digital output signals from electronic musical instruments, etc.
In a system that performs digital/analog conversion with an A converter, amplifies it with an amplifier, and outputs sound from a speaker, etc.
The present invention relates to an output adjustment device that optimally adjusts an output signal value when a power supply voltage is changed.

[Conventional technology]

With the development of digital signal processing technology, D/A converters are being used in a variety of fields. For example, a D/A converter converts a digital output signal from an electronic musical instrument, etc. into a digital/analog signal, and then converts it into an analog signal using an amplifier. There are systems that amplify the sound and emit it from speakers.

In the above-mentioned system, the amplifier is usually set so that the D waveform can be amplified to the maximum extent without being distorted. On the other hand, as a trend in electronic devices in recent years,
Systems such as those described above are often configured so that they can be used with multiple power supplies.

For example, a 12 volt AC adapter and a 9 volt battery.

In such a case, if you set the aforementioned amplifier section to achieve maximum amplification performance with a 12 volt power supply,
When switching to a 9 volt power supply, the amplifier's dynamic range becomes narrower, causing its output to become saturated and the output signal to become distorted.

As a first conventional example to prevent such a situation,
Some amplifiers are set using the power supply with the lower output voltage.

As a second conventional example, when the power supply is switched to the one with the lower output voltage, there is a system that reduces the overall value of the digital output signal before inputting it to the D/A converter.

As a third conventional example, an analog volume is provided between the D/A converter and the amplifier, and when the power supply is switched to the one with the lower output voltage, the voltage value of the analog signal input to the amplifier is reduced overall. There is something to do.

[Problem to be solved by the invention]

However, in the case of the first conventional example, the problem is that when the power supply is switched to the one with a higher output voltage, the amplifier will not be able to demonstrate its maximum amplification performance and will not be able to output sufficient volume. have.

In addition, in the case of the second conventional example, a relatively complicated circuit configuration is required, such as providing a multiplier etc. in the digital circuit section to control the digital signal value and controlling the multiplication coefficient according to the output value of the power supply. However, this method has the problem of increasing costs and increasing the size of the device. In addition, when the power supply is switched to the one with a lower output voltage, the dynamic range of the digital output signal that is D/A converted by the D/A converter becomes smaller, so the influence of quantization noise is reduced during D/A conversion. This poses a problem in that the S/N (signal-to-noise ratio) of the finally obtained analog output signal decreases.

Furthermore, in the case of the third conventional example, by providing an analog volume on the analog signal line, noise is likely to be mixed into the analog output signal at that part, and the S/N (signal This has the problem that the noise ratio (to-noise ratio) tends to decrease.

An object of the present invention is to make it possible to obtain an analog signal with a dynamic range that is capable of responding to the power supply voltage even when the power supply voltage is switched, without distorting its waveform, using a simple circuit. be.

[Means for Solving the Problems] The present invention converts a digital signal into an analog signal using a digital/analog converter, and amplifies the signal using an analog circuit such as an amplifier circuit driven by a voltage-switchable power source. This assumes a system that performs the following. The system is, for example, an electronic musical instrument system.

Further, the reference voltage varying means is provided for varying the reference voltage of the digital/analog converter according to the voltage value of the power supply. Specifically, the means is means for switching the reference voltage of the digital/analog converter when the voltage value of the power source is switched between, for example, an AC adapter and a battery. It is composed of power supply voltage detection means such as a comparator for detection, and reference voltage switching means consisting of a transistor, a diode, etc. that switches the reference voltage according to the detection result of the power supply voltage detection means. The reference voltage control means switches the reference voltage so that when the power supply voltage is high, the reference voltage is high and when the power supply voltage is low, the reference voltage is low.

In addition to the configuration of the present invention described above, the present invention can be further configured to include voltage change adjustment means for adjusting the degree of change in the reference voltage when the reference voltage is switched by the reference voltage control means described above.

[For production]

When two types of voltages, high and low, can be used as the power supply voltage, when a low power supply voltage is given, the reference voltage control means uses a digital/analog reference voltage that is lower than the reference voltage when the power supply voltage is high. Supplies the converter.

On the other hand, when a high power supply voltage is applied, the reference voltage control means supplies a reference voltage higher than the reference voltage when the power supply voltage is low to the digital/analog converter.

On the other hand, when converting each amplitude value of a digital signal into a voltage value of an analog signal, a digital/analog converter converts the reference voltage as a reference voltage.

Therefore, when the supply voltage is switched to a lower voltage and the reference voltage becomes lower, the digital-to-analog converter converts each amplitude value of the digital signal to an analog voltage that is lower than the analog voltage value that would be converted if the reference voltage was at a higher voltage. Convert to value. As a result, the dynamic range of the analog signal output from the digital/analog converter becomes smaller, so the power supply voltage that drives analog circuits such as amplifiers is switched to a lower voltage, increasing the range in which amplification can be performed without distorting the waveform. Even if the width becomes narrower, the output value will not be saturated.

Note that by adjusting the degree of change in the reference voltage when the reference voltage is switched using the voltage change adjustment means, it is possible to prevent shock noises and the like caused by switching.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The first part is a configuration diagram of an embodiment of the present invention.

In this embodiment, a digital musical tone output signal generated from a sound source 6 under the control of a CPU 5 is converted into an analog musical tone signal by a D/A converter 1, amplified by an amplifier 7, and then outputted to a speaker 8.
An example of an electronic musical instrument system that emits sound will be explained below.

Here, it is assumed that the amplifier 7 performs an amplification operation using the power supply voltage Vcc as a power supply.

In this embodiment, the power supply voltage Vcc is 12
When switched from volt to battery 9 volt, D
By lowering the reference voltage Vref supplied to the /A converter 1, the dynamic range of the analog output signal of the D/A converter 1 is reduced, and the output value of the amplifier 7 is adjusted so as not to be saturated. It is something.

In FIG. 1, a reference voltage switching unit 4 controls a reference voltage Vref to be applied to a D/A converter 1 in response to a power supply voltage switching signal supplied from an equipment power supply type output unit 2 via a switching signal rise adjustment unit 3. is switched to be high when the power supply voltage is high, and to be low when the power supply voltage is low.

On the other hand, when converting each amplitude value of the digital output signal inputted from the sound source 1 into a voltage value of an analog output signal, the D/A converter l uses a reference voltage V ref
Convert it as a reference voltage.

The equipment power supply voltage detection unit 2 is supplied with a power supply voltage Vcc for driving the entire system from an AC adapter 12.
It determines whether the voltage is 9 volts or the 9 volts supplied from the battery, and outputs a switching signal according to the determination result.

The switching signal rise adjustment section 3 is connected to the reference voltage switching section 4.
The reference voltage Vr supplied to the D/A converter 1 from
Due to sudden changes in ef.

This is a circuit section for preventing shock noise from being added to the analog output signal output from the D/A converter l.

That is, the switching signal rise adjustment section 3 controls the switching signal from the equipment power supply voltage detection section 2 so that it does not change suddenly. Thereby, the reference voltage Vref output from the reference voltage switching section 4 changes smoothly when switching the power supply.

The device power supply voltage detection section 2 is composed of a comparator centered around an operational amplifier OP. The operational amplifier OP is driven by a constant voltage VAD of approximately 5 volts, and its output is fed back to its non-inverting input terminal (+) via a resistor R3. Then, the inverting input terminal of the operational amplifier OP (
-) is supplied with a voltage value obtained by dividing the power supply voltage Vcc by resistors R4 and R5, and is grounded to the digital ground DC via a capacitor C3. on the other hand. operational amplifier OP
A voltage value obtained by dividing the reference voltage VDD by resistors R6 and R7 is supplied as a comparison reference voltage to the non-inverting input terminal (+) of , and is grounded to the digital ground DC via a capacitor C4.

The switching signal output from the operational amplifier OP of the device power supply voltage detection section 2 is input to the base terminal of the transistor TR in the reference voltage switching section 4 via the resistor R2.

A resistor R1 to which a constant voltage VAD is applied to one terminal, and a capacitor C1 to which one terminal is grounded to the analog ground AC are connected to the base terminal.

In the reference voltage switching section 4, the constant voltage VAD is applied to the emitter terminal of the transistor TR and also to the anode terminal of Dl of the diodes D1 to D3 connected in series. The collector terminal of the transistor TR and the cathode terminal of the diode D3 are connected to a capacitor C2, one terminal of which is grounded to the analog ground AC, and the voltage at the connected portion is the reference voltage Vr.
It is supplied to the D/A converter 1 as ef.

The operation of this embodiment having the above-described configuration will be described below.

First, a battery is used as a system power source, and the power supply voltage V
When 9 volts is applied as cc, the values of each element constituting the device power supply voltage detection unit 2 are adjusted so that a constant voltage VAD is output as the output of the operational amplifier OP, which is a comparator. As a result, the reference voltage switching section 4
transistor TR is turned off and the reference voltage Vr
As ef, a voltage obtained by lowering the constant voltage VAD by approximately 0.6 volt, which is the voltage drop of the diodes D1 to D3, is supplied.

On the other hand, when an AC adapter is used as a system power supply and 12 volts is applied as the power supply voltage Vcc, each component of the equipment power supply voltage detection unit 2 The element value is adjusted. As a result, the transistor TR of the reference voltage switching unit 4 is turned on, and the reference voltage V
As ref, a constant voltage VAD is directly supplied from the emitter terminal to the collector terminal of the transistor TR.

On the other hand, the D/A converter 1 is a sound? When converting each amplitude value of the digital output signal input from Ml into the voltage value of the analog output signal, the reference voltage Vref
Convert it as a reference voltage. Therefore, when the power supply voltage Vcc is switched from 12 volts to 9 volts and the reference voltage V ref becomes lower, the D/A converter 1 converts each amplitude value of the digital output signal into the reference voltage V ref.
Convert to an analog voltage value that is lower than the analog voltage value that would be converted if f was 12 volts. As a result, the dynamic range of the analog output signal output from the D/A converter 1 becomes smaller, so the power supply voltage Vcc that drives the amplifier 7 is switched from 12 volts to 9 volts, allowing amplification without distorting the waveform. Even if the possible range becomes narrower, the output value of the amplifier 7 will not become saturated.

On the other hand, when the power supply voltage Vcc is 12 volts, the reference voltage Vref becomes high and the dynamic range of the analog output signal output from the D/A converter 1 becomes large. Maximum amplification operation corresponding to the power supply voltage Vcc of volts can be performed.

In this case, the dynamic range of the digital output signal input from the sound source to the D/A converter 1 does not decrease even if the power supply voltage Vcc changes, and the quantization resolution in the D/A converter 1 also does not change. Unlike the second conventional example described above, the S/N ratio does not deteriorate in the D/A converter 1.

Further, since the reference voltage switching section 4 does not directly control the digital output signal and the analog output signal, noise is rarely directly superimposed on these signals.

Next, a specific method of adjusting each circuit portion shown in FIG. 1 will be explained.

First, in the device power supply voltage detection section 2, the operational amplifier OP
The dark value of the switching voltage at is lower than the lowest voltage when using the AC adapter, including the voltage drop of the AC adapter's regulation and the diode to prevent reverse insertion, and is lower than the highest voltage when using the battery. is set to a high intermediate value. That is, by setting the voltage to an intermediate voltage value that cannot be supplied in either case, the first
The electronic musical instrument system shown in the figure prevents situations such as oscillation due to switching of the reference voltage Vref during sound generation operation. .

Further, in the reference voltage switching section 4, the amplifier 7 and the D/A converter 1 are connected in a state where the transistor TR is on.
A resistor, a diode, etc. may be inserted on the collector side of the transistor TR to prevent oscillation.

Furthermore, the power supply voltage Vcc is switched and the transistor TR
is turned on/off, the reference voltage V ref
Shock noise is likely to be superimposed on the D/A converter 1 via the D/A converter 1. Therefore, by adjusting the time constant of the resistors R1, R2 and capacitance CI in the switching signal rise adjustment section 3 and the capacitance C2 in the reference voltage switching section 4, the rise or fall of the reference voltage V ref can be slowed down. adjust.

Specifically, for example, when the power supply voltage of an AC adapter with a rating of 12 volts is 10% of the rating and the output is 1° 4 A, the voltage is 10° including the voltage drop of 0.6 volts caused by the diode to prevent reverse plugging. When the voltage is 4 volts, the dark value voltage in the device power supply voltage detection section 2 is adjusted to 10.0 volts. For example, when the power supply voltage Vcc is 10.6 volts supplied from the AC adapter, the reference voltage V ref is 5.45 volts, and when it is 10.3 volts, the reference voltage V ref is 3°. It is said to be 83 volts.

In the above embodiment, the reference voltage V ref is 2
was configured to be able to switch between two voltage values;
It is also possible to configure the circuit so that the reference voltage Vref changes continuously in accordance with changes in the power supply voltage Vcc.

Furthermore, the present invention is not limited to electronic musical instrument systems, but can be applied to an analog circuit that converts some kind of digital output signal into an analog output signal using a D/A converter, and converts it into an analog output signal driven by a voltage-switchable power source. It can be widely applied to systems that process

〔Effect of the invention〕

According to the present invention, by varying the reference voltage according to the power supply voltage, the dynamic range of the analog signal output from the digital/analog converter can be adjusted. This makes it possible to prevent the signal processed in the analog circuit from becoming saturated.

This makes it possible to perform processing such as maximum amplification operation corresponding to the power supply voltage in an analog circuit such as an amplifier.

In this case, the dynamic range of the digital signal input to the digital/analog converter does not decrease even if the power supply voltage changes, and the quantization resolution of the digital/analog converter also does not change, so the S/N deteriorates there. This has the effect of reducing the amount of noise mixed in.

Further, since the reference voltage control means can be constructed of a comparator and elements such as transistors and diodes, the device configuration is simple, and there is also the effect of suppressing increases in cost and size of the device.

Furthermore, by adjusting the degree of change in the reference voltage when the reference voltage is switched using the voltage change adjustment means, it is possible to prevent shock noises and the like caused by switching.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention. 1...D/A converter, 2...equipment power supply voltage detection section, 3...Switching signal rise adjustment section, 4...Reference voltage switching section, 7... Amplifier.

Claims (1)

[Claims] 1) In a system in which a digital signal is converted into an analog signal by a digital/analog converter, and the analog signal is processed by an analog circuit driven by a voltage-switchable power source, the voltage value of the power source is An output adjustment device comprising reference voltage control means for varying the reference voltage of the digital/analog converter accordingly. 2) In a system in which a digital signal is converted into an analog signal by a digital/analog converter and processed by an analog circuit driven by a power supply whose voltage can be switched, when the voltage value of the power supply is switched, An output adjustment device comprising reference voltage control means for switching a reference voltage of the digital/analog converter. 3) The reference voltage control means includes: power supply voltage detection means for detecting the voltage value of the power supply; and reference voltage switching means for switching the reference voltage according to the detection result of the power supply voltage detection means. 3. The output adjustment device according to claim 2. 4) According to any one of claims 2 and 3, further comprising voltage change adjustment means for adjusting the degree of change in the reference voltage when the reference voltage is switched by the reference voltage control means. output adjustment device. 5) The output adjustment device according to claim 1, wherein the analog circuit is an amplifier circuit. 6) The system is an electronic musical instrument system, the digital signal is a digital musical tone audio signal, and the analog signal is an analog musical tone audio signal, according to any one of claims 1 to 5. output adjustment device.