JPH01253304A - Frequency modulating circuit - Google Patents

Abstract

PURPOSE:To lower the frequency of an oscillation circuit which is used to obtain the output of a prescribed frequency by increasing the frequency of the oscillation circuit via a multiplying circuit consisting of two differentiating circuits, an inverter and an OR circuit and supplying the increased frequency to a D/A converter. CONSTITUTION:The output of an oscillation circuit 1 or 2 selected by a switch 3 is supplied to a differentiating circuit 10 and an inverter 12 as well as to one of two input terminals of an OR circuit 15 respectively. The output of the inverter 12 is supplied to the other input terminal of the circuit 15 via a differentiating circuit 13. The output of the circuit 15 is supplied to a D/A converter 5 and sent out via a band pass filter 9. As a result, the oscillation frequency of the circuit 1 or 2 is doubled by a frequency multiplying circuit 18 and supplied to the converter 5. Thus the frequency of the output signal of the BPF 9 is equal to 1/8 frequency of the circuit 1 or 2 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a frequency modulation circuit that changes the oscillation frequency by switching a plurality of oscillation circuits.

[Prior Art] Fig. 5 shows a frequency modulation circuit according to a conventional technique that switches the frequencies of two oscillation circuits, for example. In Fig. 0, oscillation circuits (1) and (2) are circuits that oscillate different high frequencies, respectively. be. The switch (3) connects the oscillation circuit (1) and (
2) and input it to DA conversion 5 (5). The switch (3) is controlled by a control circuit (4). The D-A converter (5) has an oscillation port 1g (1) or (
This circuit converts the output pulse of step 2) into a step-like approximate triangular wave, and is composed of a frequency division counter (6), an exclusive OR circuit (7), and an addition circuit (8).

The output of the DA converter (5) is output through a bandpass filter (9).

In this conventional example, when obtaining a mark signal, for example, the output of the 0 oscillation circuit (1) which switches the switch (3) to, for example, the low frequency oscillation circuit (1) is input to the frequency division counter (6), and the output of the 4-bit oscillation circuit (1) is input to the frequency division counter (6). converted into a binary signal. The 4-bit binary signal is passed through an exclusive OR circuit (
7) and an adder circuit (8), the signal is converted into a step-like approximate triangular wave as shown in FIG. This approximate triangular wave is shaped into a sine wave by a bandpass filter (9) and output. 1) Select the oscillation circuit (2) that emits a higher frequency signal and input it to the DA converter (5).

According to this conventional frequency modulation circuit, the oscillation frequency of the oscillation circuit (1) or (2) is determined by the frequency division counter (6).
) is reduced to 1716.

[Problems to be Solved by the Invention] Since the conventional frequency modulation circuit divides the oscillation frequency by a frequency division counter, the output frequency becomes lower than the oscillation frequency. Therefore, when a high frequency is required as the output frequency, an oscillation circuit with an extremely high oscillation frequency is required, and when a crystal oscillator or the like is used as the oscillation circuit, it becomes expensive.

[Means for Solving the Problems] The frequency modulation circuit of the first invention selects one of at least two oscillation circuits that oscillate rectangular wave signals of different frequencies by a switch means, and Either the rising edge or the falling edge of the rectangular wave signal of the selected oscillation circuit is detected by a first differentiating circuit, and the phase of the rectangular wave signal of the selected oscillation circuit is inverted by an inverter to detect the rising edge or the falling edge of the output signal. Either one is detected by a second differentiating circuit, and the multiplier circuit includes an OR circuit that receives the outputs of the first differentiating circuit and the second differentiating circuit as input, and the output of the OR circuit is sent to a D-A converter. It is configured to perform D-A conversion.

Further, in the frequency modulation circuit of the second invention, one of at least two oscillation circuits that oscillates rectangular wave signals of different frequencies is selected by a switch means, and the phase of the rectangular wave signal of the selected oscillation circuit is adjusted. The outputs of the 11 inverters are inverted by the first inverter, the outputs of the 11 inverters are integrated by the first integrating circuit, the phase of the output of the first integrating circuit is inverted by the second inverter, and the output of the second inverter is integrated by the second inverter. an exclusive OR circuit which integrates the signal by an integrator circuit, inverts the phase of the output of the second integrator circuit by a third inverter, and receives the rectangular wave signal of the selected oscillation circuit and the output of the third inverter as input; The output of the exclusive OR circuit is DA-converted by a DA converter.

[Function J The oscillation frequency of the oscillation circuit is multiplied by each multiplier circuit.

[Embodiment] In Fig. 1, which shows the configuration of an embodiment of the frequency modulation circuit according to the first invention, oscillation circuits (1) and (2) are oscillation circuits using, for example, crystal oscillators, and are generally oscillation circuits. (
As an example of the zero oscillation frequency where the frequency of oscillation circuit (1) is lower than the frequency of oscillation circuit (2),
0KHz, and the oscillation circuit (2) is 11KHz. The switch (3) is a changeover switch for selecting either the oscillation circuit (1) or (2), and is controlled by the control circuit (4). The oscillation circuit (
The output of 1) or (2) is the capacitor → no °ct and the resistor R1.
A differentiating circuit (10) and an inverter (12) consisting of
) respectively. The output of the differentiating circuit (10) is inputted to one input terminal of the OR circuit (15) via the buffer (11), and the output of the inverter (12) is input to the differentiating circuit 1B (
13) and is input to the buffer (14). The output of the buffer (14) is input to the other input terminal of the 012 circuit (15). The output of the OR circuit (15) is D
-A converter (5). D-A converter (5)
is composed of a frequency division counter (6), an exclusive OR circuit (7) into which the output of the frequency division counter is input, and an addition circuit (8) that adds the outputs of the exclusive OR circuit (7). The output of the DA converter (5) is output through a bandpass filter (9).

Next, the operation of this embodiment will be explained.

FIG. 2(a) shows the output waveform of the oscillation circuit (1) or (2). The oscillation waveform of FIG. Further, the emitted Wt signal inverted by the inverter (12) shown in FIG. 2(c) is differentiated by the differentiating circuit (13) and then
The waveform is shown in figure (d). Differential circuit (10) and (1
The output waveforms of 3) are buffered (11) and (1), respectively.
4), respectively, as shown in Figures 2(e) and (f).
The waveform is shown in . The waveforms in FIG. 2(e) and FIG. 2(f) are combined by an OR circuit (15) to form the waveform shown in FIG. 2(g). As a result of the above processing, the frequency of the waveform shown in FIG. 2(g) is 2 times the frequency of the waveform shown in FIG. 2(a).
Double. The output of the 0R1i1i1 path (15) is input to the frequency division counter (6), and the output of the 0 frequency division counter (6), whose frequency is divided by 1/16, is input to the exclusive OR circuit (7).
) and then added by an adder circuit (8), resulting in a stepped triangular wave as shown in FIG. This triangular wave is filtered by a bandpass filter (
9), the waveform is shaped and output as a sine wave.

In this embodiment, the oscillation frequency of the oscillation circuit (1) or (2) is doubled by the frequency multiplier circuit (18) and input to the D-A converter (5), so that The frequency of the output signal is determined by the oscillation circuit (1) or (2)
Each frequency is 1/8 of the frequency of .

FIG. 3 shows a second embodiment of the present invention.

In this embodiment, the frequency multiplier circuit (18) is composed of three inverters (20a), (20b), (
20c), two sets of integrating circuits (22a), (22b)
and an exclusive OR circuit (21). The operation of this embodiment is shown in FIGS. 4(a) to 4(a).
This will be explained using the waveform g).

In the figure, the waveform in FIG. 4(a) is the waveform of the output signal of the oscillation circuit (1) or (2). This signal is input to the first terminal of the exclusive OR circuit (21). The waveform shown in FIG. 4(b) is a waveform obtained by inverting the phase of the oscillation signal from the oscillation circuit using an inverter (20a). The waveform of FIG. 4(b) becomes the waveform shown in FIG. 4(C) by the integrating circuit (22a). A signal having the waveform shown in FIG. 4(C) is input to the inverter (20b). FIG. 4(d) shows the output waveform of the inverter (20b), and this waveform is out of phase with the output waveform of the oscillation circuit shown in FIG. 4<a>. The signal having the waveform shown in FIG. 4(d) is further transformed into the waveform shown in FIG. 4(e) by the integrating circuit (22b). This waveform signal is further passed through an inverter (20
c). The output waveform of the inverter (20c) is shown in FIG. 4(f), and a signal having the waveform shown in FIG. 1I(f) is input to the second terminal of the exclusive OR circuit (21). As a result, the output waveform of the exclusive OR circuit is as shown in Figure 4(g).0As is clear from Figure 4, the frequency of the signal with the waveform shown in Figure 4(g) is as shown in Figure 4(a). It is twice the frequency of the waveform signal. In contrast to the above two embodiments, the frequency multiplier circuit (18) doubles the frequency of the input signal and outputs it, but the frequency can be further multiplied by connecting a plurality of frequency multiplier circuits.

[Effect of the invention] According to the invention, the frequency of the oscillation circuit is controlled by two differentiating circuits,
I)-A Since the signal is configured to be input to the converter, the frequency of the oscillation circuit for obtaining an output of a predetermined frequency can be lowered. As a result, a crystal oscillator with a low oscillation frequency can be used, which simplifies the circuit configuration and reduces costs.

[Brief explanation of the drawing]

Figure r151 is a configuration diagram of the frequency modulation circuit of the embodiment of the first invention of this invention, Figure 2 (a), Figure 2 (b), Figure 2 (C), Figure 2 (d), 2(e), 2(f), and 2(g) are waveform diagrams for explaining the first invention in detail, and FIG. 3 is a configuration of an embodiment of the second invention of this invention. The circuit diagrams shown in Fig. 4(a), Fig. 4(b), Fig. 4(c)
), FIG. 4(d), FIG. 4(e), FIG. 4(f), and FIG. 4(g) are waveform diagrams showing the operation of the second invention, and FIG. 5 is a frequency diagram according to the conventional technology. FIG. 6 is a block diagram showing the configuration of the modulation circuit, and is a waveform diagram of the output of the D-A converter of the frequency modulation circuit, which is common to the present invention and the prior art. In the figure, (1) and (2) are oscillation circuits, (3) is a switch means, (5) is a D-A converter, (10) and (13) are differentiating circuits, (12) is an inverter, and (15) is an OR circuit, (18) is a multiplier circuit, (20a), (20b)
, (20c) is an inverter, (22a), (22
b) is an integrating circuit.

Claims (2)

[Claims] (1) At least two oscillation circuits that oscillate rectangular wave signals of different frequencies, a switch means for selecting one of the at least two oscillation circuits, and a rising or falling edge of the rectangular wave signal of the selected oscillating circuit. a first differentiating circuit that detects either one of the above; an inverter that inverts the phase of the rectangular wave signal of the selected oscillation circuit;
A second differentiating circuit that detects either the rising edge or the falling edge of the output signal of the inverter, a multiplier circuit that includes an OR circuit that receives the outputs of the first differentiating circuit and the second differentiating circuit, and an OR circuit. A frequency modulation circuit including a D-A converter that D-A converts the output of. (2) at least two oscillation circuits that oscillate rectangular wave signals of different frequencies; switch means for selecting one of the at least two oscillation circuits; and inverting the phase of the rectangular wave signal of the selected oscillation circuit. 1st
an inverter, a first integrator circuit that receives the output of the first inverter as an input, a second inverter that inverts the phase of the output of the first integrator circuit, and a second integrator that receives the output of the second inverter as an input. a third inverter that inverts the phase of the output of the second integrating circuit, and a multiplier circuit comprising an exclusive OR circuit whose inputs are the rectangular wave signal of the selected oscillation circuit and the output of the third inverter; D converts the output of the exclusive OR circuit from D to A.
- A frequency modulation circuit comprising an A converter.