JPS5912820Y2 - Symmetrical triangular wave generation circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a symmetric triangular wave generation circuit used as an energy spread signal in an FM modulation system.

According to the regulations of the International Satellite Communication Organization (Intelsat),
The Frequency Division Multiplexed Telephone Frequency Modulation (FDM-FM) radio waves transmitted from each earth station are equipped with an energy spread signal to reduce interference with terrestrial lines and to reduce cross-modulation noise of common amplifiers within the satellite. modulation is required.

This energy spread signal varies from 20H2 to 150H2
It is defined as a symmetrical triangular wave with a specified frequency (deviation ±1H2) between

The conventional symmetrical triangular wave generation circuit of the energy diffusion signal generation circuit has a double base diode 1 as shown in Fig. 1.
The output pulse of the repeating pulse generation circuit consisting of the L variable resistor 12, the capacitor 13, and the resistor 14 drives the flip-flop circuit 15 to obtain a rectangular wave, which is further converted into a triangular wave through the integrating circuit 16, and then converted to a triangular wave by the variable resistor 17. The desired signal was obtained at the output terminal 1 by adjusting the level.

However, this circuit has two drawbacks as shown below.

That is, one of them is that the oscillation frequency is set by the variable resistor 12.
Therefore, in order to set the specified frequency ±I Hz and the degree, it must be done while measuring the output frequency, which is troublesome. Due to the fact that the triangular wave is obtained by integrating the wave, the amplitude of the triangular wave changes in inverse proportion to the frequency, and in order to compensate for the amplitude change when setting the frequency, a variable resistor is used while measuring the output level. It is necessary to adjust the device 17.

At Intelsat, operational plans often change.
At that time, the frequency designation of the energy spread signal is also changed, so it is very inconvenient to have to make adjustments that require a measuring instrument at that time.

In order to avoid this inconvenience, it is possible to use a switch to switch fixed resistors instead of the variable resistors 12 and 17 in this circuit, but in order to obtain the required frequency accuracy, it is necessary to ±1% is insufficient, and it is necessary to use a special high-precision resistor, which is disadvantageous in terms of price and manufacturing delivery time.

SUMMARY OF THE INVENTION An object of the present invention is to provide a novel energy diffusion signal generation circuit that eliminates the above-mentioned drawbacks of the conventional circuit and allows accurate and easy setting of the frequency of an energy diffusion signal.

The present invention is a symmetrical triangular wave generation circuit characterized by having a variable frequency triangular wave oscillation circuit including a digital-to-analog conversion circuit, an integrating circuit, and a Schmidt-Dricker circuit with a polarity switching function.

The present invention will now be described in detail with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of the present invention.

In the figure, reference number 21 is a switch group, 22 is an 8-bit digital-to-analog conversion circuit with a polarity switching function, and 2
Reference numeral 4 indicates an integrating circuit, and reference numeral 25 indicates a Schmitt trigger circuit.

As such a digital-to-analog conversion circuit 22,
There is an integrated circuit μPC610C (manufactured by Nichiden).

This switch group 21 has eight circuits of switches, and the open/open state of each switch is determined by the digital-to-analog conversion circuit 22.
The logic state of the digital input terminal of “1” and “099”
connected to correspond to

Therefore, by opening and closing each switch appropriately,
It can represent an 8-bit binary number, which is 1
If expressed in decimal notation, numbers from 0 to 255 can be expressed.

The output voltage of the digital-to-analog conversion circuit 22 is a voltage whose absolute value is proportional to this input numerical value.

The polarity of this output voltage is controlled by the output of the Schmitt trigger circuit 25 connected to the polarity switching input, and when the output of the Schmitt trigger circuit 25 is positive, the output voltage of the digital-to-analog conversion circuit 22 is positive. is connected to the integrating circuit 24, and the output of the Schmidt) Lica circuit 25 is □
When the voltage is negative, the output voltage of the digital-to-analog conversion circuit 22 is connected to the integration circuit 24 with negative polarity.

Now, assuming that the output of the Schmidts)) Rica circuit 25 is positive, the output voltage of the digital-to-analog conversion circuit 22 is integrated by the integration circuit 24, and the output of the integration circuit 24 increases in proportion to time.

When the voltage reaches the upper limit value of the Schmitt trigger circuit 25, the output voltage of the Schmitt trigger circuit 25 is inverted and becomes negative.

Then, the polarity of the input voltage of the integrating circuit 24 is reversed by the action of the polarity switching function of the digital-to-analog conversion circuit, so that the output voltage of the integrating circuit 24 changes from increasing to decreasing.

Then, when the voltage reaches the lower limit value of the Schmidt circuit 25, the output of the circuit 25 is inverted again.

In this way, the output of the integrating circuit 24 becomes a triangular wave,
It is taken out from output terminal 1.

Its amplitude is determined by the voltage difference between the upper and lower limit values of the Schmidts)) circuit 25 and is a constant value.

Moreover, the frequency is proportional to the amplitude of the input voltage of the integrating circuit 24.

As described above, the oscillation frequency of the triangular wave oscillation circuit shown here is proportional to the output voltage of the digital-to-analog conversion circuit 22, so that an output with a frequency proportional to the numerical value of the digital input can be obtained.

Therefore, in the circuit of FIG. 2, its proportionality constant is I
Hz, the output frequency can be changed from 1H2 to 255 Hz by setting the switch group 21.
It is clear that it can be set in Hz intervals.

The accuracy of this setting depends on the accuracy of the conversion characteristics of the digital-to-analog conversion circuit 22 and the linearity of the control of the voltage frequency of the triangular wave oscillation circuit, but within the range of 20 Hz to 150 Hz required for the energy diffusion signal, ± It is easy to obtain an accuracy of 1H2.

As explained above, according to the circuit of the present invention, when changing the frequency of the energy diffusion signal, it is possible to change the frequency of the energy diffusion signal by simply setting the switch group, and there is no need for a measuring device. Since it is always constant and does not require adjustment, it has an extremely large practical effect in operation.

Furthermore, since digital-to-analog conversion circuits with a polarity switching function that are integrated circuits are now available at low cost, the transmitter can also be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a conventional circuit diagram, and FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, 1... Output terminal, 11...
・Variable resistor, 12...Capacitor, 13...
...Double base diode, 14...Resistor, 15...Flip-flop circuit, 16.
...Integrator circuit, 17...Variable resistor, 2
1...Switch group, 22...Digital-to-analog conversion circuit, 24...Integrator circuit, 25
・・・・・・Schmitt trigger circuit.

Claims (1)

[Scope of utility model registration request] A digital-to-analog conversion circuit that generates analog voltages having analog values and polarities corresponding to the input parallel digital signal and the input polarity switching signal, respectively, an integration circuit for time-integrating the output of this digital-to-analog conversion circuit, and an output of this integration circuit. a Schmitt trigger circuit connected thereto, and means for supplying the output signal of the Schmitt trigger circuit as the polarity switching signal to the digital-to-analog conversion circuit, A symmetrical triangular wave generating circuit characterized in that a triangular wave is generated at the output of the circuit.