JPS5930277B2 - waveform generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveform generator that generates a waveform consisting of a plurality of different frequency components that are in a harmonic (integral multiple) relationship with each other.

Waveforms consisting of a plurality of different frequency components that are harmonically (integer multiples) related to each other are often required in electronic musical instruments and other fields of electronic engineering.

However, until now, a waveform generator with a simple configuration that can stably generate such a waveform has not been realized. especially,
It is actually possible to create a waveform generator with a simple configuration that can arbitrarily control the frequencies of each frequency component that makes up a waveform while maintaining a harmonic relationship with each other and keeping the relative level of each frequency component constant. It was said that This invention was made in view of the above-mentioned circumstances, and it generates a waveform consisting of a plurality of different frequency components that are in a harmonic relationship with each other based on a single clock, and it is possible to change the frequency of the clock. The object of the present invention is to provide a waveform generator with a simple configuration that allows the frequencies of each frequency component to be arbitrarily controlled while maintaining a mutual harmonic relationship and keeping the relative level constant. be.

Therefore, the waveform generator according to the present invention includes one or more digital RC filters, frequency dividing means for dividing an input clock to generate a timing pulse for controlling the switching timing of the digital RC filter, and A digital signal that receives an input clock and generates an analog signal containing harmonic components of the timing pulse.
It is characterized by comprising an analog converting means, the analog signal is input to the digital RC filter, and the output of the digital RC filter is taken out as an output waveform signal. The above and other objects and features of the present invention will be made clear by the following description of embodiments.

The waveform generator of the present invention can of course be applied to general waveform generation applications, but can also be used extremely effectively as a musical tone signal generator in an electronic musical instrument, as will be described later. The present invention will be described below based on several embodiments, but first a digital RC filter will be described.

FIG. 1 shows an example of a parallel switching type digital RC filter and its peripheral circuit.

Input terminal Ti and output terminal T of digital RC filter F
A resistor R is connected in series to the signal line between the signal line and the output terminal TO, and four capacitors C are connected between the output terminal TO side of the signal line and the ground, respectively, via transistors Tr. These transistors Tr can be replaced with other switching elements such as field effect transistors or even mechanical switches. Further, the number of capacitors C is not limited to four, but any number may be provided. Each transistor Tr is sequentially turned on at a fixed timing. In this example, the clock input to the clock terminal Tc is input to a 2-bit binary counter 1, and the output of each bit of this counter 1 is supplied to a digital RC filter F as a timing pulse. A decoder 2 provided in the digital RC filter F generates drive pulses Sl, S, , S3, S4 based on the timing pulses, and each transistor Tr is sequentially driven by the drive pulses S1 to S4. The timing relationship between each of the drive pulses S1 to S4 and the clock is as shown in FIG. In addition, in this example, the digital RC filter F is equipped with a decoder 2, but the timing pulse is applied to each transistor Tr.
The decoder 2 is not necessary in the case of a configuration that can directly drive the . This digital RC filter F exhibits a comb-like filter characteristic having a large number of pass bands b as shown in FIG.

The center frequencies of each pass band b are in harmonic (integer multiple) relationship with each other, and the timing pulse or drive pulse S1~
This corresponds to each harmonic number of S4. The bandwidth BW of each pass band b is expressed by , and is determined by the values of the resistor R and capacitor C.

Further, the relative gain A at the center frequency of each pass band b is expressed as '.

T However, sampling interval γ=-, sampling period T
=- (see Figure 2).

F p As is clear from equation (2) and FIG. 3, the digital RC filter F of this example has drive pulses S1 to S4
The frequency 4f, which is four times the frequency 4f, is an integer multiple of the frequency 4f,,8fp,
12f, . . . have no pass band.

Note that equations (1) and (2) can be generalized as follows.

\- However, N is equal to the number of capacitors C, and the clock frequency is Nf.

As mentioned above, the digital RC filter has a comb-like filter characteristic consisting of a large number of passbands with a center frequency equal to each harmonic frequency of the timing pulse. However, the above relationship does not change, and the relative gain of each pass band also remains unchanged.

In addition to the parallel switching type, there are also series switching types of digital RC filters, and both are applicable to the present invention. Furthermore, such a digital RC filter is described in various documents, such as the American magazine ElectrOn.
Since it was introduced in the July 24, 1967 issue of ICS (Electronics), pages 91 to 100, and is already well known, further explanation of the operating principle and modifications will not be given. Referring to FIG. 4, an embodiment of the waveform generator according to the present invention will be described.

In the figure, FO, F,,...,Fn-,
are digital RC filters, each having the same configuration as the digital RC filter F in FIG. (n+
1) The bit binary counter 10 receives a clock (frequency: 2n+1·F,
), and each digital RC filter F constitutes a frequency dividing means for dividing the frequency. , Fl, . . . , Fn-1 timing pulses are generated. This binary counter 10
The outputs of the 1st and 2nd bits, the outputs of the 2nd and 3rd bits, the outputs of the nth bit and the (n+1)th bit are the outputs of each digital signal, respectively. R
C filter F. , Fl, . . . , Fn-, as a timing pulse. The digital-to-analog converter 11 together with the binary counter 10,
Each digital RC filter F based on the clock. ,F
This constitutes a digital-to-analog conversion means for creating an analog signal containing each harmonic of the timing pulses 1, . . . , Fn-1. This digital-to-analog converter 11 receives the output of each bit of the binary counter 10 and generates a step-like analog signal with a repetition period of 1/Fp as shown in the lower left part of FIG. Of course, each digital RC filter F is applied to this analog signal. , F, , . . . , each harmonic component of the timing pulse of Fn-1 is included. This analog signal is sent to each digital RC filter F. , Fl, ......,
Fn-1 is commonly input to each digital RC filter F. , Fl, . . . , Fn-1, the output is a variable resistor R as an addition resistor. ,Rl,...,Rn-
After being added by 1, it is taken out from the output terminal 0UT. Next, the operation of this embodiment will be explained.

If the frequency of the input clock is 2n+1・F, then the first
digital RC filter F. Since the frequency of the timing pulse supplied to is 2F・F,, 2l・F,
This digital RC filter F. The frequency of the drive pulses (corresponding to S1, S2, S3, and S4 in FIG. 1) generated inside is 2l·Fp. Therefore, this digital RC filter F. have center frequencies F and F, respectively.
,2fp,3f,,5fp96fpra7FpF9fpF
It exhibits comb-like filter characteristics consisting of a large number of passing bands of ゛゜゜゜゜゛. Also, since timing pulses of frequencies 21·Fp and 22·F are supplied to the second digital RC filter F1, this digital RC filter F1
have center frequencies of 2f, 4fp, 6f, 10, respectively.
It exhibits comb-like filter characteristics consisting of a large number of pass bands f, 12fp, 14fp, 18f, . . . . Similarly, the digital RC filter Fn-1 has a center frequency of 2n-1, FP, 2n-F, 2n+1, respectively.
・F,,2n+3・F,,2n+4・FP,2n+5・
It exhibits comb-like filter characteristics consisting of a large number of pass bands: FP, 2n+7.FP, 2n+8.F, . . . .

The harmonic components of each timing pulse included in the analog signal created by the digital-to-analog converter 11 are filtered through each digital RC filter F. ,F,,...
, Fn-1, the variable resistance R is extracted according to the filter characteristics of Fn-1. , R, . . . , Rn-1 and output to the output terminal 0UT. That is, a waveform signal consisting of harmonic components of each timing pulse can be obtained at the output terminal 0UT. And each digital RC filter F. , Fl, ..., Fn-1, the relationship between the center frequency of each pass band and the clock frequency always holds even if the clock frequency is changed, and the relative gain of each pass band is also The analog signal obtained by the digital-to-analog converter 11 is constant regardless of the clock frequency, and the analog signal obtained by the digital-to-analog converter 11 is always connected to each digital RC filter F even if the clock frequency is changed. ,Fl,...
. , Fn-1, and the relative level of each harmonic component is always constant. Therefore, according to this embodiment, a composite waveform consisting of a plurality of different frequency components that are harmonically related to each other can be obtained based on a single clock, and while maintaining the harmonic relationship of the frequency components, each frequency component is The frequency of each frequency component can be changed arbitrarily by changing the frequency of the clock while keeping the relative level constant. In other words, the fundamental frequency of the waveform obtained by this embodiment changes in accordance with the clock frequency, but the state of the spectrum distribution with respect to the fundamental frequency of this waveform is constant regardless of the clock frequency. Note that the state of the spectrum distribution of the output waveform is determined by the variable resistor R. , Rl, . . . , Rn-1 are adjusted to form each digital RC filter F. ,Fl,...
..., can be changed by changing the mixing ratio of the output of Fn-1. In the previous embodiment, the frequency dividing means for generating the timing pulse was a binary counter, so the frequency of the obtained timing pulse was a power of 2 times F,
That is, Fp, 2f,, 4fp, 8fp, l6f, .
It is limited to...

Similarly, since the digital-to-analog conversion means that generates the analog signal input to each digital RC filter is composed of a binary counter and a digital-to-analog converter, the frequency components included in the analog signal are ,,4f,,8f,,l6f,,...
It is limited to the frequency components of... Therefore,
The waveforms that can be generated in the previous example are F,, 2fp to 4fpp.
It is limited to those composed of frequency components of 8 fp, 16 fp, F32 fp2, and so on. Such limitations are overcome according to another embodiment of the invention shown in FIG.

In this embodiment, each digital RC filter F.
．． , F, . ,Dl,...
..., Dn-1 and n 1/2 frequency dividers D. ,dl,
..., Dn-1, and each digital RC filter F. , Fl, ..., Fn-
3, Fn-, , Fn-, have their first pass band center frequencies FP92fP'1109(n-
3) Timing pulses are supplied such that FP (n-2) Fp (n-1) Fp. That is, each frequency divider D. ,D,,...,Dn-,,Dn-2,Dn
-1 is the frequency 2fp'4fpp112(n]
)Fp2(n-,)F,,2(n-,)F, pulses are output.

The frequency of the clock input to the clock input terminal 1N is determined by each frequency divider D. ,Dl,...,Dn-,
corresponds to the least common multiple of the frequencies of the output pulses. Conversely, each frequency divider D. , Dl, . Further, in this embodiment, each digital RC filter F. , Fl
, . . . , the analog signal containing the harmonics of the timing pulse of Fn-1 is processed through a digital loop consisting of a counter 12 that receives the clock as an input, and a digital-to-analog converter 11 that receives the output of this counter 12 as an input. generated by analog conversion means. Specifically, n
= 2, frequency divider D.

, Dl, D, are 1/2, 1/3, 1/2, respectively.
6, the clock frequency is 1゛2f, and the counter 12 is a hexadecimal counter. As is clear from the above explanation, in this embodiment, each digital R
C filter F. ,Fl,...,Fn-3,Fn
The center frequencies of the first passband of -2, Fn-1 are Fp, 2fp, ......, 2(n-,)F,, 2
(n-2)F, ,2(n-1)F, and each digital RC filter F. ,F,,...,Fn-
3, Fn], Fn-1 has the frequency FP92fP9Fll
92(n-3)Fp'2(n-2)Fp92(n-,)
Since an analog signal containing the Fp component and its harmonic components is input, a waveform having a continuous spectrum distribution can be obtained. The waveform generating device of the present invention as described above is extremely effective as a musical tone signal generating means for, for example, an electronic musical instrument. FIG. 6 shows an example of an electronic musical instrument to which the waveform generator of the present invention is applied. In the figure, 20 is a keyboard circuit, 21 is a voltage controlled oscillator, 22 is a waveform generator of the present invention, 23 is a voltage controlled amplifier, 24
is a power amplifier, 25 is a speaker, and 26 and 27 are envelope generators. When a specific key is pressed, a pitch voltage corresponding to the key is output from the keyboard circuit 20,
The oscillation frequency of the voltage controlled oscillator 21 is controlled by this pitch voltage. The oscillation output of voltage controlled oscillator 21 is supplied to waveform generator 22 as a clock. The output of the waveform generator 22 is input to a power amplifier 24 via a voltage-controlled amplifier 23, where the power is amplified and then output to a speaker 25.
is pronounced as a musical tone. The envelope generators 26 and 27 generate an envelope voltage in response to a key ink signal output from the keyboard circuit 20 during a key press period. The gain of the voltage-controlled amplifier 23 is controlled by the output of one of the envelope generators 27, which gives musical tones a time-varying amplitude characteristic similar to natural musical instrument sounds such as attack, fast decay, sustain, and second decay. will be granted. Furthermore, the oscillation frequency of the voltage-controlled oscillator 21 is controlled by a minute amount by the output of the other envelope generator 26, giving the musical tone a time-varying pitch characteristic similar to that of a natural musical instrument. As described above, the fundamental frequency of the waveform signal generated by the waveform generator 22 according to the present invention changes faithfully following the frequency of the input clock, but on the other hand, the spectrum of the waveform signal The distribution remains unchanged even if the clock frequency changes.

That is, if the waveform generator of the present invention is used as a musical tone signal generator, a musical tone signal with a constant spectral distribution state can be obtained no matter which key is pressed, and therefore a musical tone with the same timbre can be obtained no matter which key is pressed. is obtained. Incidentally, in order to change the timbre of musical tones in accordance with the passage of time from the time of sound generation in the electronic musical instrument shown in FIG. 6, it is only necessary to partially change the configuration of the waveform generator 22.

FIG. 7 shows an example of the waveform generator 22 that has been modified as described above, in which the digital-to-analog converter 11
The output is sent to each digital RC filter F via a newly provided voltage leg type filter 28. ,Fl,...
, is input to Fn-1. This voltage controlled filter 2
The filter characteristics of 8, such as the cutoff frequency, are determined by the envelope generator 29 which operates in response to the key ink signal.
It is made to change over time by the control voltage (envelope voltage) output from. It is clear that this allows the timbre of musical sounds to change over time. In FIG. 7, the same parts as those in FIG. 4 are given the same reference numerals. As described in detail above, the waveform generator of the present invention has a simple configuration and can generate a waveform consisting of a plurality of different frequency components that are harmoniously related to each other based on a single clock. By changing , the frequency of each frequency component can be arbitrarily controlled while maintaining a harmonic relationship with each other and keeping the relative level constant, and the effect is enormous.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a known digital RC filter, FIG. 2 is a timing chart explaining the operation of the digital RC filter shown in FIG. 1, and FIG. 3 is a circuit diagram of the digital RC filter shown in FIG. FIG. 4 is a block diagram of one embodiment of the waveform generator according to the present invention, FIG. 5 is a block diagram showing another embodiment of the waveform generator according to the present invention, and FIG. FIG. 7 is a block diagram showing an example of an electronic musical instrument to which the waveform generator according to the invention is applied. FIG. 7 is a block diagram showing a modification of the waveform generator shown in FIG. FO, F,...Fn-1...Digital RC filter, 10...Binary counter, 11...Digital-to-analog converter,
RO, R,,...,Rn-1...Variable resistor, 12...Counter, DO, DlF''?6
″″″FDn-r1″3 frequency divider 1d0Fd1F10)D
n-1...1/2 frequency divider.

Claims (1)

[Scope of Claims] 1. A switching type digital RC filter, means for dividing a clock to generate a timing pulse for controlling the switching timing of the digital RC filter, and a means for generating a timing pulse for controlling the switching timing of the digital RC filter in response to the clock; a waveform generating device comprising: means for generating an analog signal including a wave component, and outputting the analog signal through the digital RC filter. 2 means for dividing the frequency of a clock to generate a plurality of sets of timing pulses of different frequencies; a plurality of digital RC filters each receiving the timing pulses and performing switching at different speeds; and means for receiving the clocks and generating the respective sets of timing pulses. A waveform generator comprising means for generating an analog signal containing a harmonic component of a timing pulse and commonly inputting it to each of the digital RC filters, and means for adding and outputting the outputs of the digital RC filters.