JPH0420196B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electronic sound generation circuit that adds an envelope to a digital melody waveform signal, and particularly to an electronic sound generation circuit that adds an envelope to a digital melody waveform signal. This invention relates to an electronic sound generation circuit.

In recent years, it has been proposed to add envelopes to these electronic sounds using various envelope generation circuits in order to obtain more natural sounds when generating melodies, ticking sounds, chime sounds, etc. using electronic sounds. There is.

Conventional circuits for generating envelopes can be roughly divided into analog circuits that use capacitors and resistors and use the capacitor's charging and discharging waveforms;
There was something digital that could be incorporated inside an IC.

An example of these conventional examples and their drawbacks will be explained below.

One example is a method in which envelope information from a waveform ROM that stores desired envelope information is multiplied by a melody signal using a multiplier, and the multiplied signal is converted into analog by a DA converter.

Using a multiplier in this manner has the disadvantage that the processing speed of the multiplier is slow and it cannot follow high frequencies.

In addition, since the circuit itself becomes large-scale, the area occupied by the circuit becomes large, and in order to generate the minimum attenuation sound, it is necessary to use DA.
The number of bits in the converter must be increased,
It was difficult to drive at low voltage.

On the other hand, there were some that added an envelope by controlling the gain etc. of an amplifier external to the IC by varying the value of the resistor built into the IC, but it was difficult to match the resistor inside the IC and the amplifier. In addition, if the number of stages for the envelope is large, the number of built-in resistors in the IC must be increased.

Furthermore, a method has been proposed in which an envelope is added by changing the reference voltage of the DA converter in order to eliminate the drawbacks of the above method. An example of this will be explained using FIG. 1st
The DA converter 2 in the figure is composed of a voltage division ladder resistor type, and each switch S ₁
~S _o corresponds to each bit input of the waveform ROM 4.

Further, an envelope generating circuit 6 is connected to the reference input of the DA converter 2.

This is when the DA converter 2 outputs a waveform signal based on the waveform memory value in the waveform ROM 4.
The DA converter 2 is controlled by an envelope signal from an envelope generating circuit 6 to add an envelope to a waveform signal.

However, as the envelope generating circuit 6, the second
When using a CR time constant circuit consisting of a capacitor 8, a resistor 10, and a transistor 12 as shown in the figure,
Since the capacitor 8 and the resistor 10 are external components of the IC, complete integration is not possible and the cost increases.

Further, since such a CR time constant circuit can only obtain one attenuation waveform, it is not possible to cope with complex volume changes such as those of musical instrument sounds. If the CR time constant circuit is used as the envelope generation circuit 6 in this way, various problems will occur, so this envelope generation circuit 6 should also be used.
It has also been proposed to integrate a combination of a ROM and a DA converter, and further configure the data in the ROM so that it can accommodate complex volume changes.

However, when the envelope generation circuit 6 is configured with a ROM and a DA converter in this way, the input resistance value seen from the reference input side of the voltage division ladder resistance type DA converter 2 to which the envelope generation circuit 6 is connected is Switch S ₁ ~ _{S o}
Since the output varies depending on the ON/OFF state, the linearity of the output of the DA converter in the envelope generating circuit 6 is lost, causing a problem in that the volume cannot be varied according to the data.

In order to provide an envelope generating circuit 6 that is not affected by the input resistance value of the DA converter 2 and can be further integrated, a problem has arisen in that an extremely complicated circuit configuration is required.

The present invention uses a voltage division ladder resistance type DA converter for converting digital signals from a volume ROM that stores melody volume information, that is, envelope information, into an analog signal. By using a current addition ladder resistance type DA converter as a DA converter that converts a digital signal into an analog signal, the drawbacks and problems of the conventional example can be solved, it can be easily integrated, and it can be easily integrated. The purpose of the present invention is to provide an electronic sound generation circuit that can also respond to melodies and their envelopes. An embodiment of the present invention will be described below based on the drawings. FIG. 3 is a diagram showing a case where an embodiment of the electronic sound generating circuit of the present invention is applied to the ticking sound of an electronic clock. First, the configuration of the electronic sound generation circuit portion of the present invention and the functions and characteristics of its constituent elements will be explained.

14 is a melody waveform ROM in which predetermined melody waveform data is stored as a digital signal.

Reference numeral 16 denotes a melody address counter for reading data stored in the melody waveform ROM, and is driven by a clock signal output from a scale frequency dividing circuit, which will be described later.

18 is a melody volume ROM in which melody volume data, that is, envelope data is stored as a digital signal.

Reference numeral 20 denotes an envelope address counter for reading data stored in the melody volume ROM 18, and is driven by a clock signal output from an envelope frequency dividing circuit to be described later.
22 is a voltage division ladder resistance type DA converter (hereinafter referred to as voltage ladder) in which resistors with resistance values of Re and 2Re are connected in a ladder shape, and converts the digital signal from the melody volume ROM 18 into an analog signal. It is.

As shown in FIG. 4, this voltage ladder 22 corresponds to each bit input b ₀ to b _o-1 of the melody volume ROM 18 and each switch S ₀ to S o _{- 1} , respectively. _o-1 goes to ground when the bit signal is “0”, and goes to the reference voltage when it is “1”.
Operates to connect to V _S.

This voltage ladder 22 is the melody volume ROM 18
The resistance value seen from the output side is constant _Re regardless of the bit pattern.

Therefore, the equivalent circuit becomes as shown in FIG. 5. Assuming that the load connected to the output terminal of this voltage ladder 22 is R _L , the voltage applied to this load is V _put
becomes as follows.

V _put =R _L /R _L +R _e V _DD (b _o-1 /2 + b _o-2 /2 ² +…
...+b ₁ /2 ^n-1 +b ₀ /2 ⁿ ) bi=0or1 (i=0, 1,..., n-1) From the above formula, the output voltage V _put is (R _L /R _L +R _e )
It will vary from V _DD to 0.

Note that the resistance value when viewed from the side of each switch S ₀ to S _o-1 changes depending on the bit pattern, so the reference voltage V _S in this example is connected to a constant voltage source V _DD to be influenced by it. It is configured so that there is no such thing.

In Figure 3, 24 is a current addition ladder resistance type in which resistors with resistance values R _n and 2R _n are connected in a ladder shape.
This is a DA converter (hereinafter abbreviated as current ladder), which converts the digital signal from the melody waveform ROM 14 into an analog signal.

This current ladder 24, as shown in FIG.
Each bit input b ₀ to b _o-1 of melody waveform ROM 14
The switches S ₀ to S _o-1 are set to correspond to each other, and the switches S ₀ to _{S o-1} connect to the ground when the bit signal is “0” and to the current when it is “1”. - It is set to be connected to the resistor 26 for voltage conversion.

This current ladder 24 is set so that the resistance value viewed from the reference voltage V _EV side is constant R _n regardless of the bit pattern of the melody waveform ROM 14 .

Therefore, the summed current output is:

I _put = V _EV /R _n (b _o-1 /2 + b _o-2 /2 ² +...+b ₁ /2
^n-1 + _b0 / ²ⁿ ) bi=0or1 (i=0, 1,..., n-1) The output of the voltage ladder 22 described above is connected to the reference voltage input of the current ladder 24 in this embodiment. ing.

The current ladder 24 has a constant resistance R _n when viewed from the reference voltage input, and the voltage ladder 22 has a constant resistance R _e when viewed from the output side, so these are connected as shown in Figure 3. Then, it can be represented by an equivalent circuit as shown in FIG.

In the circuit shown in FIG. 7, the load resistance R _L of the circuit shown in FIG. 5 is changed to R _n .

Therefore, the voltage V _EV applied to the current ladder 24
is, V _EV = R _n /R _n + R _e V _DD (b _o-1 /2 + b _o-2 /2 ² +…+
b ₁ /2 ^n-1 + b ₀ /2 ⁿ ) bi=0or1 (i=0, 1,..., n-1).

According to the above formula, the voltage V _EV is (R _n /R _n +R _e )V _DD
The melody volume changes only according to the information in the ROM 18 in the range from 0 to 0, and the current ladder 24
It is not affected by the ON/OFF status of the switches S ₀ to S _o-1 .

On the other hand, since the current ladder 24 is given V _EV as a stable reference voltage, the linearity of the DA converter is not lost.

Therefore, the current ladder 24 and the voltage ladder 22 connected to this reference input operate effectively only as envelope additions without adversely affecting each other.

Furthermore, the current ladder 24 is adjusted so that R _n /R _e.
By setting the resistance value of the voltage ladder 22,
Since the value of R _n /R _n +R _e approaches 1, the range of the voltage V _EV can be increased as the resistance value of the current ladder 24 increases.

The above-mentioned melody waveform ROM 14, melody address counter 16, melody volume ROM 18,
The envelope address counter 20, the voltage ladder 22, and the current ladder 24 are the constituent elements of the electronic sound generation circuit of this embodiment, and as described above, the voltage ladder 22 and the current ladder 24 can be operated without affecting each other's output. , which outputs an output signal according to the data.

Next, referring again to FIG. 3, the operation of each component of the above embodiment will be explained together with the electronic timing operation.

In FIG. 3, 28 is a reference signal generator such as a crystal oscillator, 30 is a frequency dividing circuit that appropriately divides the reference signal from the reference signal generator 28, and 32 is a frequency dividing circuit 3.
Waveform shaping circuit for shaping the signal from 0, 34
is a drive circuit that drives the motor 36, and 38 is a wheel train driven by the motor 36.

40 is a reference mechanism, and on the hour the wheel train 38
It is turned on by the movement of .

42 is a timing control circuit, and the reference mechanism 40 is
When turned on, the melody address counter 16 and the envelope address counter 20 described above are enabled, and the envelope frequency dividing circuit 44 and scale frequency dividing circuit 46 are also activated.

When the envelope frequency dividing circuit 44 and the scale frequency dividing circuit 46 operate in this manner, the envelope address counter 20 and the melody address counter 16 operate, and read envelope data and waveform data from the melody volume ROM 18 and the melody waveform ROM 14, respectively.

The data read from the melody volume ROM 18 is converted to voltage output by the voltage ladder 22, and when the switch S _o , which is turned ON when adding an envelope, is turned ON, the reference voltage is applied to the current ladder 24 from the voltage ladder 22. be done.

Further, the data read from the melody waveform ROM 14 is converted into a current I _put by a current ladder 24 to which a reference voltage from a voltage ladder 22 is applied.

The current I _put output from the current ladder 24 is converted from current to voltage via a resistor 26 and is then converted to an amplifier 48.
The amplifier 48 drives the speaker 50 to generate a tapping sound when the envelope is applied. Such reading of data from the melody volume ROM 18 is performed for each time-beating operation, and a pulse signal is output from the envelope address counter 20 to the number-of-strokes counter 52 each time reading is performed. Ru.

The stroke counter 52 counts the signal from the envelope address counter 20, and this count value is compared with the count value of the count counter 54 in a matching circuit 56.

The contents of the counting counter 54 are determined in advance by operating the counting switch 60 to activate the counting control circuit 58.

When the coincidence circuit 56 outputs a coincidence signal, the time striking control circuit 42 controls the melody address counter 16,
The envelope address counter 20, envelope frequency dividing circuit 44, and scale frequency dividing circuit 46 are all stopped. Then, the hour control circuit 42 outputs a pulse signal to the counting control circuit 58, and this signal causes the counting control circuit 58 to add 1 to the contents of the counting counter 54 in preparation for the next hour. The operation ends.

The striking sound obtained in this way is a combination of the melody waveform stored in the melody waveform ROM 14 and the envelope stored in the melody volume ROM 18, and it is possible to obtain a tone that is very close to natural. It is something.

Note that application to electronic watches is just one example, and the electronic sound generating circuit of the present invention can also be used for musical instruments and the like.

According to the present invention, since the envelope can be added to the melody inside the IC, the IC
Since no external parts are required, the area occupied by the circuit can be reduced, and costs can also be lowered by reducing the number of parts and improving assembly workability. Further, since the envelope generating section of the present invention is composed of only a combination of a resistor network and a switch element, it can be used even at a low voltage such as 1.5V, and can be widely used in small portable devices.

Furthermore, the shape of the envelope can be freely changed simply by changing the stored contents of the memory, and a wide range of sounds from the natural world, such as bird calls and the sound of waves, to the sounds of musical instruments such as the piano, can be generated using the same circuit. I can do it. Furthermore, since the rise of the sound can be made steeper than with the CR method, it is possible to produce a particularly good feel of the hitting sound.

As described above, the present invention provides an electronic sound generation circuit that enables integration using two DA converters and is configured so that the AD converters do not adversely affect each other.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a device using a conventional envelope addition method, FIG. 2 is a diagram showing a conventional example of the envelope generating circuit shown in FIG. 1, and FIG. Diagram applied to the beat sound,
Figure 4 shows the voltage division ladder resistance type DA shown in Figure 3.
The characteristic explanatory diagram of the converter, Fig. 5, is shown in Fig. 4.
6 is a diagram showing the characteristics of the current addition ladder resistance type DA converter shown in FIG. 3, and FIG. 7 is a diagram showing an equivalent circuit of the DA converter shown in FIG. 3. 14...Melody waveform ROM, 16...Melody address counter, 18...Melody volume
ROM, 20... Envelope address counter, 22... Voltage division ladder resistance type DA converter, 24... Current addition ladder resistance type DA converter.

Claims (1)

[Claims] 1. A melody waveform ROM in which melody waveform data is stored as a digital signal; A melody volume ROM in which melody volume data is stored in a digital signal; An address counter for reading data from both ROMs; a first DA converter that converts data from the melody volume ROM into an analog signal; and a second DA converter that converts data from the melody waveform ROM into an analog signal using the signal from the first DA converter as a reference input. ; a sound generation circuit that generates sound by the output of a second DA converter; and; in the electronic sound generation circuit, the first DA converter is constituted by a voltage division ladder resistance type DA converter with a constant output resistance; An electronic sound generation circuit characterized in that the DA converter is a current addition ladder resistance type DA converter with a constant input resistance.