Title:
FREQUENCY DIVIDER CIRCUIT FOR PRODUCING A SUBSTANTIALLY SAWTOOTH WAVE
United States Patent 3654558


Abstract:
A tone signal source especially for electronic musical instruments having a plurality of output terminals for producing a nearly sawtooth wave output signal is composed of a plurality of frequency divider units each comprising a frequency divider circuit and a mixing circuit connected in such a manner that all of the frequency divider circuits included in the frequency dividing units are connected in cascade, and one of the input terminals of each mixing circuit is connected to an input terminal of the circuit or to the output terminal of the preceding mixing circuit, and the other input terminal thereof is connected to the output of the frequency divider circuit belonging to the output of the frequency divider circuit belonging to the same frequency dividing unit, so that a plurality of the output signals can be obtained from the output terminals of these mixing circuits.



Inventors:
TOMISAWA NORIO
Application Number:
05/007837
Publication Date:
04/04/1972
Filing Date:
02/02/1970
Assignee:
NIPPON GAKKI SEIZO KK.
Primary Class:
Other Classes:
84/677, 327/126, 327/135, 984/325
International Classes:
G01S13/28; G01S13/76; G10H1/08; H03B19/14; H03K4/02; (IPC1-7): H03K21/00
Field of Search:
328/16,22,25,30,35,36,39,181,186 307
View Patent Images:



Foreign References:
FR1241636A1960-09-16
Primary Examiner:
Krawczewicz, Stanley T.
Claims:
I claim

1. A circuit for producing a substantially saw-tooth wave from an input including a square wave, comprising: a plurality of electronic frequency divider units connected in cascade and each with an input point and an output point and adapted to produce an output frequency corresponding to half that of its input; and at least as many electronic frequency mixer units, also connected in cascade and each having a first and second input terminal and an output terminal; means interconnecting the two cascades such that the second input terminal of each mixer unit is electrically connected to the output terminal of the corresponding divider unit, and the first input terminal of a first mixer unit is electrically connected to the input terminal of the first divider unit; and a plurality of alternative output terminals connected individually in succession at least to the output terminals of the mixer units whereby at successive output terminals an increasingly closer approximation to a saw-tooth wave is obtained.

2. The circuit as claimed in claim 1, which includes a circuit means generating a triangular wave of the same frequency as said square wave to be mixed with the triangular wave, said circuit means which generates a triangular wave being connected to the first input terminal of said first mixer unit, so that a triangular wave is mixed with a divided frequency square wave to produce waveforms progressively closer to an ideal saw-tooth wave.

3. The circuit as claimed in claim 2 wherein said circuit means generating a triangular wave receives a stepped wave and includes: a differential circuit comprising a transistor; a first resistor and a first capacitor in parallel and connected to the base of the transistor; a second resistor connected to the collector of the transistor and through which resistor a stepped input wave is fed in; and a second capacitor connected across the emitter and collector of said transistor.

Description:
BACKGROUND OF THE INVENTION

This invention relates generally to a frequency divider circuit for obtaining output signals closely approximating a saw-tooth waveform, which is advantageously applicable in electronic musical instruments as a tone signal source.

As a frequency divider circuit to be employed as a tone signal source in an electronic musical instrument, a circuit having flip-flop circuits or blocking oscillation circuits connected in series has been heretofore known. However, the output of each of the former circuits is of a square waveform, thus lacking higher harmonics of even orders in such a waveform so that it is deficient for the purpose of tone formation in the instrument. On the other hand, each of the latter circuits does not have such a shortcoming, but it has a drawback in that the oscillation frequency is easily varied depending on the spontaneous allowance variation of the circuit elements (capacitors, resistors, etc.) included in the time-constant circuit, or variations in the voltage on temperature.

Furthermore, when the circuit is synchronized and employed as a 1/2 frequency-dividing circuit, the values of the circuit elements must be specifically designed for each of the desired operational frequency ranges, whereby manufacture is difficult if the output frequency is extended over several octaves or more. Furthermore, the capacitors in the circuit must be made larger for the lower frequency ranges of the circuit, and this increases the cost of the capacitors, resulting in further difficulty in combining into other portions of the instrument.

SUMMARY OF THE INVENTION

Therefore, the primary object of the invention is to provide a novel organization of the frequency divider circuit for obtaining a nearly saw-tooth wave tone signal source wherein all of the above described drawbacks of the conventional frequency divider circuit are substantially eliminated.

Another object of the invention is to provide a novel construction organization of a frequency divider circuit for obtaining a nearly saw-tooth wave employed for a tone signal source wherein the above described necessity of separating providing circuit elements for each of the frequency ranges is completely eliminated.

These and other objects of the present invention can be achieved by a novel organization of the frequency divider circuit which comprises a plurality of frequency divider units, each of the units further comprising a frequency divider circuit and a mixing circuit having two input terminals, one of the input terminals of the mixing circuit included in the first frequency divider unit being connected to the input terminal of the frequency divider circuit included in the same unit, and the other input terminal of the same mixing circuit being connected to the output of the said frequency divider circuit, in the second and the subsequent frequency divider units, each of the first input terminals of the mixing circuits being connected to the output terminal of the preceding mixing circuit and each of the second input terminals of the mixing circuits being connected to the output terminal of the frequency divider circuit included in the same frequency divider unit, whereby output signals each having 1/2 frequency of the preceding signal and being much nearer to the saw-tooth waveform can be obtained from the output terminals of the mixing circuits.

The nature, principle, and utility of the invention will be more clearly understood from the following description with respect to a preferred embodiment thereof, when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram showing a frequency divider circuit according to the present invention which is employed for producing a nearly saw-tooth wave form signals;

FIGS. 2(a) through 2(g) are waveform charts showing the waveforms obtained from various output terminals of the frequency divider circuit shown FIG. 1 in the case where a square wave is applied to the input terminal of the circuit;

FIG. 3 is a circuit diagram showing the frequency divider circuit of FIG. 1 combined at the input terminal thereof with a further circuit producing a substantially triangular wave to be applied to said input terminal;

FIGS. 4(a) through 4(g) show waveforms which may be obtained at points a, b, c, d, e, f and g, respectively, of the circuit shown in FIG. 3; and the circuit to obtain an input signal having a triangular waveform shown in FIG. 4(a),

FIG. 6 is an explanatory diagram of an electronic frequency mixer unit.

DETAILED DESCRIPTION OF THE INVENTION

In the example of the frequency divider circuit shown in FIG. 1, D1, D2, and D3 are 1/2 frequency divider circuits in which are employed for instance, flip-flops. M1, M2, and M3 are mixing circuits of a kind as shown in FIG. 6 wherein two mixing resistors Rm of an equivalent value are connected across each of the two input terminals a' and b' and a middle point of the connection, respectively, and, at the same time, a buffer transistor Qm is connected between the middle point of the connection and an output terminal Om in a manner to be operative as an emitter follower.

Furthermore, an input terminal of the first frequency divider circuit D1 and an input terminal a' of the first mixing circuit M1 are connected to an input terminal a of this circuit, and the other input terminal b' of the mixing circuit M1 is connected to an output terminal b of the frequency divider circuit D1, whereby a first frequency dividing unit U, is constituted.

Second and third frequency dividing units U2 and U3 are also constituted in the same manner as described with respect to the first frequency dividing unit U, and the input terminals of respective stages of the frequency dividing units U1, U2, and U3 are connected to the output terminals b, d, f, .... . Likewise, one of the input terminals of each of the mixing circuits is connected to the corresponding output terminal such as c, e, g, ... of the preceding mixing circuit so that the mixing circuits also are thereby connected in cascade.

Now, supposing that a square wave as shown in FIG. 2(a) is applied to the input terminal a of this circuit, the square wave input signal is frequency divided by one-half shown in FIG. 2(b) by means of the first frequency dividing circuit D1. Since the output terminal b of the circuit D1 is connected to the input side of the mixing circuit M1 together with the input terminal a, a stepped wave as shown in FIG. 2(c) is created at the output terminal c of the mixing circuit M1.

In this case, the circuit is so arranged that the amplitude level of the square wave (crest value) from the input terminal a and the amplitude level of the square wave from the output terminal b of the frequency divider portion D1, are in a ratio of 0.5:1 when mixed to be a mixed resultant signal. Since the square wave shown in FIG. 2(b) which has been frequency divided by one-half is further frequency divided by one-half by means of the second frequency divider D2, still another square wave as shown in FIG. 2(d) is obtained from the output terminal d of the second frequency divider portion D2. This square wave is then mixed with a stepped wave as shown in FIG. 2(c) obtained from the first mixing circuit M1, in the second mixing circuit M2 (at a level ratio of 1:1), so that another stepped wave as shown in FIG. 2(e) can be obtained.

Similar operations are repeated in the third frequency divider unit U3 employing a level ratio of 1:1, and a stepped wave as shown in FIG. 2(g) which closely resembles a saw-tooth wave (herein called a nearly saw-tooth wave) and has been obtained by a repeated frequency division of the square wave shown in FIG. 2(a). If the number of the frequency dividing units connected in cascade is increased, the resultant wave may be further frequency divided and a closer approximation to a saw-tooth wave can be obtained. According to the present invention as described above, a required number of frequency dividing units each consisting of a frequency dividing circuit and a mixing circuit are connected in cascade, so that an input frequency is thereby divided successively, and the waveform thereof is gradually brought nearer to a saw-tooth wave.

Since the tone colors of different music instruments are not very different each other in the treble (high frequency) range, and because the auditory sense of human ear is rather dull for the difference in tone-color in the treble range, waveforms such as those obtained from the terminals c and e are sufficiently good for practical use as high frequency tone sources. Furthermore, the accuracy or similarity to a saw-tooth wave in lower tone ranges can be raised as shown in FIG. 2(g), whereby the circuit as indicated in FIG. 1 is highly adapted for use as a tone signal source in an electronic musical instrument.

Although in the above description, it is assumed that square wave a is applied to the input terminal of the circuit, the input is not necessarily of a square waveform and for instance, a triangular wave as shown in FIG. 4(a) may also be employed for this purpose. In such a case, the mixing level ratio in the mixing circuit M1, is selected at 1:1, whereby a waveform as shown in FIG. 4(c) can be obtained at the output terminal c of the circuit, and, likewise, nearly saw-tooth waves as shown in FIG. 4(e) and 4(g) can be obtained from the respective output terminals e and g of the circuit shown in FIG. 1. The waveform shown in FIG. 4(a) can be obtained in a manner described below with reference to FIG. 3 and FIGS. 5(a) through 5(c). A transistor Q is normally cut off and a cut-off bias voltage is applied to the base thereof by the resistor R1. Input signals are differentiated to be converted to plus and minus pulses shown in FIG. 5(b) by a differential circuit composed of a capacitor C1 and resistor R1. Each of aforementioned plus pulses cause currents to flow instantly to the base of the transistor Q, to turn it on, and to discharge capacitor, C2 with a time constant C2 RQ (where RQ is the internal resistance of the transistor Q) of a very small value as shown in FIG. 5(c), while each of the minus pulses have no influence on the operation of the transistor Q.

Moreover, since the capacitor C2 is charged during the OFF state of the transistor Q, the output signals at the terminal OUT in FIG. 3 become triangular waves in FIG. 5(c), with the values of capacitor C2 and resistor R2 set to a suitable value, and the time constant integrated by the load of the capacitor C2 and resistor R2 being small to some extent. The signals thus obtained in FIG. 5(c) are nearly equal to the signals shown in FIG. 4(a).

As is clearly seen from the drawings, the proximity to the saw-tooth waveform in the case of FIG. 4 is better than that of the preceding case. This fact indicates that the nearer the input waveform is to the triangular wave, the nearer are the output waveforms to the saw-tooth wave, thus rendering the outputs advantageous for use as tone signal sources. It should be noted that a provision is made in the circuit according to the present invention so that the mixing level ratio in the mixing circuit M1 is varied in accordance with the waveform of the input signal into a suitable value for rendering output waves nearer to the saw-tooth waveform.