JPS6214518A - Analog signal generator - Google Patents

Abstract

PURPOSE:To obtain an output signal of low distortion rate having a prescribed frequency with a simple circuit constitution by approximating the sine wave output to a triangular wave. CONSTITUTION:The input signal applied to an input terminal 6 passes an input means 1 and sets the counted value of a programmable counter 2. The counter 2 counts the clock from a clock generating means 3; and when the counted value reaches said set value, the counter 2 is reset by itself and inverts the polarity of an integrating circuit 4. The circuit 4 generates a voltage output, which changes linearly with time, in an output terminal 5 in accordance with a prescribed time constant, and the voltage change is inverted simultaneously with coming of a polarity inverting signal. Thus, the triangular wave corresponding to the input code is sent from the terminal 5. Since harmonic components of the triangular wave are a half of those of a staircase approximate waveform, a special filter is unnecessary or only a very simple filter is required.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an analog signal generator, and in particular to a tone dialer for a telephone. The present invention relates to an analog signal generator.

[Conventional technology]

Conventionally, this type of analog signal generation device has used a preset counter to down-currently clock a clock signal from a crystal oscillator or the like, and synthesized it into a sine wave using step-like approximation using a D/A. At this time, since the counting period of the preset counter is determined according to the digital input signal, it is possible to obtain an analog output having a highly accurate frequency.

Currently, many ICs having this type of function are in practical use.

[Problem that the invention seeks to solve]

The above-mentioned conventional analog signal generator synthesizes sine waves by staircase approximation, so it uses a series-parallel DAC to set the level corresponding to each step of the staircase and a so-called Johnson counter to drive the DAC. A conversion circuit and the like are required, resulting in a very complicated circuit configuration. Since the staircase-approximated sine wave has the characteristic that harmonic components caused by the clock are attenuated by a slope of 6 dB10 ct, for example, it is used in telephones where the in-band distortion rate standard is required to be 120 dR or less. When used as a tone dialer, it is necessary to set the harmonic components outside the band by increasing the clock frequency, or to use a high-order low-pass filter. In the former case, the number of steps in the staircase increases and the wave becomes closer to a sine wave, but it is necessary to increase the number of stages of the serial-to-parallel conversion circuit and DAC, making the circuit even more complicated. Moreover, deterioration of frequency accuracy is inevitably accompanied. The latter results in a more complex internal circuit and an increase in the number of external components (mainly capacitors).

[Means for solving problems]

The present invention has been made in view of the conventional drawbacks as described above.

The present invention includes an input signal input means, a preset counter whose counting period is set by the input signal, an integrating circuit whose polarity is inverted by the output signal of the preset counter, and a time constant of the integrating circuit which is set according to the input signal. The present invention provides an extremely simple analog signal generating device characterized in that it includes means for generating a triangular wave and generates a triangular wave having a frequency corresponding to the input signal.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows an embodiment of the invention. In the figure, 1 is an input signal input means, 2 is a programmable counter, and 3 is a programmable counter.
is a clock generation means, 4 is an integration circuit, 5 is an output terminal, 6
indicates an input terminal. The input signal applied to 6 is passed through input means 1 to set the count value of programmable counter 2. The programmable counter 2 counts the clock from the clock generating means 3, and at the same time as it reaches the count value, it resets itself and further inverts the polarity of the integrating circuit 4. The integrating circuit 4 operates according to a predetermined time constant.
A voltage output that changes linearly with respect to time is produced at the output terminal 5, but the voltage change is reversed simultaneously with the above-mentioned polarity inversion signal train.

In this way, a triangular wave having a period corresponding to the input code is sent out from the output terminal 5.

In this case, it is easy to understand that if the time constant of the integrating circuit 40 is always constant, the output signal obtained will have an amplitude inversely proportional to the frequency.

In order to always obtain a constant output level regardless of the input signal, it is a good idea to change the time constant of the integrating circuit 40.

This can be easily realized by setting the circuit constants (resistance, capacitor, constant current value, etc.) of the integrating circuit 4 according to the input signal so that the time constant is proportional to the frequency.

Furthermore, since the triangular wave has half the harmonic components as compared to the staircase approximation waveform, a special filter is not necessary, or even if it is necessary, it may be a very simple one.

〔Effect of the invention〕

As described above, the present invention makes it possible to obtain an output signal with a predetermined frequency and a low distortion rate by approximating a sine wave output to a triangular wave, using an extremely simple circuit configuration compared to the conventional circuit.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention. In the figure, 1... input means, 2... programmable counter, 3... clock generation means, 4...
...Integrator circuit, 5...Output terminal, 6...
...Input terminal. Figure 2 (al shows the output waveform at a constant time constant, and Figure 2 (b) shows the output waveform at time constant adjustment. , -1,\ Agent Patent Attorney Susumu Uchihara −＼ゝ・r

Claims (1)

[Claims] means for inputting an input signal, a preset counter whose counting period is set by the input signal, an integrating circuit whose polarity is inverted by the output signal of the preset counter, and a time constant of the integrating circuit is set according to the input signal. 1. An analog signal generating device comprising means for generating a triangular wave having a frequency according to the input signal.