JPS6155802B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal conversion device that converts a rectangular wave into a sine wave.

Currently, there is a standard called the Kansas City Standard, which is one of the efforts to standardize the data recording method for recording data from a microcomputer onto an audio cassette tape. This means that data “1” is 2400Hz and “0” is 1200Hz.
After converting to a square wave of 2400Hz and
It is modulated into a 1200Hz sine wave and recorded serially onto an audio cassette tape. However, some modulation circuits supply the above two types of rectangular waves to a common low-pass filter and convert them into sine waves, but this has a phase shift and a 1200
The disadvantage is that the output levels of Hz and 2400Hz sine waves are different. In addition to this, there are also filters that use two bandpass filters, 1200Hz and 2400Hz.
This has the disadvantage of being structurally complex.

Furthermore, what the above two examples have in common is that
Since the rectangular wave is directly supplied to the filter, its harmonic components are generated, causing malfunctions.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a signal converting device which converts a rectangular wave into an approximate trapezoidal wave or triangular wave and then into a sine wave with an extremely simple configuration, thereby eliminating the above-mentioned drawbacks of the prior art.

An embodiment of the present invention will be described below based on the drawings. In Fig. 1, 1 is a microcomputer;
2 is a conversion circuit constituting the pulse generation circuit;
Receive data from microcomputer 1,
It converts "1" and "0" into rectangular waves that are pulses to be converted at 2400 Hz and 1200 Hz, respectively.
This rectangular wave is synchronized with the level inversion of the logical values "1" and "0" from the microcomputer 1, and the time of level inversion of the logical value and the rise of the rectangular wave are always synchronized. 3 is a phase conversion circuit, which shifts the phase of the output pulse from the conversion circuit 2 by 1/4 cycle. 4 is a clock pulse generation circuit, which has built-in hexadecimal and hexadecimal counters, etc., and generates 12 pulses in synchronization with the rising and falling edges of the pulse from the phase conversion circuit 3, and the logic value is inverted from the microcomputer 1. When this happens, six pulses are generated from this inversion. 5, 6, 7
8 is a gate circuit, 8 is an inverter, and 9 is a tri-state bus driver constituting a switching circuit. This bus driver 9 is well known from ``Electronic Science Series'' 71 ``CMOS Application Techniques,'' and its specific configuration will be omitted, but its operation is such that when the gate input is "1", the input passes through. When the gate input is "0", the input is cut off and the impedance becomes high. 10 is a charging/discharging circuit, which includes a resistor 11 and a capacitor 1.
Consists of 2. 13 is a low-pass filter, 14 is an amplifier, and 15 is a magnetic head.

Next, the operation will be explained. When data (101) is generated from the microcomputer 1 as shown in FIG. 2A, eight 2400Hz rectangular pulses are generated within one bit of data "1" from the conversion circuit 2 as shown in FIG. 2B, and data "0" is generated from the conversion circuit 2. “Within 1 bit of
Four 1200Hz rectangular pulses are generated. The phase of this rectangular pulse is shifted by 1/4 period by the phase conversion circuit 3, and the pulse shown in FIG.

On the other hand, when the output of the microcomputer 1 is "0", the gate circuit 6 is opened by the output of the inverter 8, and the third
The clock pulse P ₁ in Figure D...P ₁ is the gate circuit 6,
Pass 7. Note that FIGS. 3A, B, and C are enlarged views of the time scales of FIGS. 2A, B, and C, respectively. Also, the clock pulse P ₁ ...P ₁ is
It is set so that 12 pulses are generated within a half period of the pulse shown in FIG. 3C from the phase conversion circuit 3. When the input of the bus driver 9 (pulse shown in Figure 3C) is "1", each time the clock pulse _P1 ... _P1 is supplied, the above input "1" passes and its output becomes "1". , is charged to the charging/discharging circuit 10. Furthermore, when the clock pulse is not supplied, the bus driver 9 has a high impedance, so the charging/discharging circuit 1
The output voltage of 0 rises in a stepwise manner as shown in FIG. 3E. Then, when the input of the bus driver 9 becomes "0" and clock pulse _P1 ... _P1 is supplied, the output of the bus driver 9 becomes "0" each time it arrives, and the charge in the charge/discharge circuit 10 increases. It discharges and its output voltage drops stepwise.

In this way, the 1200Hz rectangular pulse is converted into the stepwise pulse _P3 shown in Figure 3E, which is passed through the low-pass filter 1.
3, it becomes a sine wave _S1 , and is recorded on a cassette tape (not shown) via an amplifier 14 and a magnetic head 15.

Next, the output of microcomputer 1 is “1”
Then, the converter circuit 2 converts the 2400Hz shown in Figure 2B.
This is converted into a rectangular pulse, which is sent to the phase conversion circuit 3.
The signal is supplied to the bus driver 9 with its phase shifted by 1/4 period. On the other hand, microcomputer 1
The gate circuit 5 is opened by the above output "1",
Clock pulses P _{2 .} . . P ₂ of FIG. This clock pulse P ₂ . . . P ₂ is set to have the same pulse width as _{the previous clock pulse P 1 .} Moreover, when the output level of the microcomputer 1 is inverted, six pulses are generated from this inversion by the operation of the hexadecimal counter. Therefore, at the output of the charging/discharging circuit 10, a stepped pulse _P4 having a period exactly 1/2 of the period of the previous stepped pulse _P3 is generated as shown in FIG. 3E. This step-like pulse P ₄ is also filtered by low-pass filter 1.
3, it becomes the sine wave _S2 shown in FIG.

In this way, the 1200Hz and 2400Hz rectangular waves in Figure 2B are converted to the sine waves S ₁ and S ₂ in Figure 2D, and when the sine waves S ₁ and S ₂ switch, one cycle of each ends. It always matches the time, and there is no phase shift or distortion from the start to the end.

By the way, to adjust the amplitude of the stepped pulse,
This can be easily done by adjusting the pulse width and number of clock pulses _P1 ... _P1 , _P2 ... _P2 .

Note that in the above embodiment, the rectangular wave is once converted into a trapezoidal stepped pulse, but the present invention is not limited to this, and it may be converted into a triangular stepped pulse. In this case, the clock pulse may be constantly supplied to the bus driver 9.

Also, in the above example, “0” and “1” are respectively
Although the conversion is performed to 1200Hz and 2400Hz, the conversion is not limited to this, and may be converted to 2400Hz and 4800Hz, for example.

By the way, the basic formula of the trapezoidal wave as shown in Figure 4 is expressed as i=4E/π (sin sin+1/9 sin3 sin30 +1/25 sin5 sin50+...), so the clock pulse P ₁ ...P ₁ ,
P ₂ .... By setting the duty of P ₂ and the constant of the charging/discharging circuit 10, if the stepped pulses P ₃ and P ₄ are set to = π/3, the harmonic component three times that amount will be In order to prevent such occurrence, the low-pass filter 13 may be one that blocks harmonic components of five times or more, for example, a filter whose cut-off frequency is set to about 8000 Hz. In this way, this low-pass filter can be used commonly over a wide range, and "0" and "1" can be set to 2400Hz.
Also, there is no need to make any design changes when converting to 4800Hz.

Furthermore, an analog switch or the like may be used instead of the bus driver 9.

As described in detail above, according to the present invention, rectangular converted pulses having different periods are generated according to the logical values "1" and "0", and the phase is different from that of the converted pulse.
The pulse shifted by 1/4 period is input to the switching circuit, and when the clock pulse arrives, the input is supplied to the charging/discharging circuit to generate a stepped pulse, which is then passed through a filter, resulting in an extremely simple circuit configuration. A sine wave with no distortion or phase shift can be obtained.

Furthermore, when converting two or more types of converted pulses with different periods, the switching circuit supplies the same number of clock pulses within one period of each converted pulse, so the period of the converted pulses is switched. In this case, the signal can be converted to a sine wave without phase distortion from the point of switching.

Furthermore, the amplitude of the sine wave can be easily adjusted by appropriately setting the width and number of clock pulses.

Furthermore, since the wave is first converted into a trapezoidal wave or a triangular wave and then passed through a filter, its harmonic components can be easily removed, and a common filter can be used over a wide area.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention, FIGS. 2 and 3 are time charts for explaining the operation, and FIG. 4 is a waveform diagram of a trapezoidal wave. 2... Pulse generation circuit, 3... Phase conversion circuit,
4...Clock pulse generation circuit, 9...Switching circuit, 10...Charging/discharging circuit, 13...Filter.

Claims (1)

[Scope of Claims] 1. Conversion that converts logical values "1" and "0" into converted pulses of duty 1/2 in rectangular shapes with different periods, each having a changing point synchronized with the changing point of this logical value. a phase conversion circuit that shifts the phase of the converted pulse by 1/4 period and switches the period of the converted pulse at the center of the converted pulse; A clock pulse generation circuit generates a constant number of clock pulses with a constant pulse width within a half period of A signal conversion device consisting of a switching circuit whose input side and output side are cut off, a charging/discharging circuit connected to the output side of this switching circuit, and a filter receiving the output of this charging/discharging circuit.