JPS594296Y2 - Oscillation circuit for information transmission in trains and other vehicles - Google Patents

Description

[Detailed explanation of the invention] This invention is an oscillator for information transmission in vehicles such as trains that modulates the oscillation frequency in the direction of the specific frequency when facing a resonant circuit of a specific frequency placed at a predetermined point on the vehicle running route. It relates to circuits and aims to improve the waveform of a constantly oscillating frequency signal in the oscillation circuit.

The so-called frequency-variable automatic train stop (approximately shifting ATS) device, as illustrated in Figure 6, uses an amplifier AM for level limiting.
P and a power amplifier PA having a phase characteristic are connected in cascade, and a part of the output of the power amplifier PA is transmitted through the two loosely coupled coils 11 and 12 of the on-board receiving antenna AT. An oscillation circuit that constantly oscillates at a constant oscillation frequency is constructed by providing positive feedback to the input terminal of the amplifier AMP, and a receiver circuit DT that monitors the change in the oscillation frequency of the oscillation circuit is mounted on the vehicle, and furthermore, A resonant circuit RC, which is a ground element with a frequency different from the constant oscillation frequency, is disposed at a required point above, and when the receiving antenna AT of a running train passes over this resonant circuit RC, the oscillation on the train is When the constant oscillation frequency of the circuit changes in the direction of the resonant frequency of the resonant circuit RC, a receiving circuit DT detects this change in frequency, thereby detecting the point of frequency change and automatically applying train braking. It is.

Therefore, the information transmission oscillation circuit that changes the oscillation frequency in the direction of the resonance frequency of the resonance circuit RC is widely used not only for ATS but also for detecting the type of vehicle or the state of the vehicle traveling point. .

Conventionally, in the above-mentioned variable station type oscillation circuit, in order to improve the constantly oscillating signal waveform, as shown in FIG.
A resonant circuit was constructed by connecting a capacitor C in parallel to a transformer T of an amplifier circuit consisting of a transistor Tr at the output stage of the level limiting amplifier AMP, a coupling transformer T, etc. in FIG. 6, as shown in the figure.

The amplitude and phase characteristics of the waveform in this circuit are shown in FIG.

That is, FIG. 11a is an amplitude characteristic diagram showing the amount of amplitude attenuation with respect to frequency, and FIG.

(Hz) is the constant oscillation frequency, and fn (Hz) is the maximum frequency that can be modulated.

In order to better improve the waveform, it is necessary to increase the sharpness Q of the resonant circuit shown in Figure 1.
Frequency f, respectively indicated by solid lines in figures a, l).

The attenuation amount and phase difference based on (stop) are respectively indicated by the dotted lines at the frequency f.

(stop) increases.

This results in a decrease in modulation sensitivity and a decrease in the variable frequency band, resulting in disadvantages that are contradictory to waveform improvement and expansion of the variable frequency band.

The present invention provides the variable frequency oscillation circuit described above, which has a pass band near the constant oscillation frequency and the variable frequency frequency, exhibits a maximum value of attenuation in a frequency band outside the pass band, and By using a filter with a characteristic that the phase difference of the waveform is within ±90°, it is possible to improve the waveform without reducing the variable frequency band, and the above-mentioned drawbacks of the conventional method are eliminated.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is an example of a circuit diagram of a filter BPF used in the present invention, with an inductance L.

The circuit of capacitance C6 and capacitance C6 always has an oscillation frequency f.

In the passband circuit, the relationship is as follows.

Of course, there is a similar frequency relationship below.

Figure 4 is a characteristic diagram of the filter BPF shown in Figure 3.
Figure a is an amplitude characteristic diagram showing the relationship with the amount of attenuation of frequency, and the same figure is a change characteristic diagram of the input/output phase difference with respect to changes in frequency.

In other words, the filter BPF has a frequency of 0. fo, f2. f4. It has a pass band near each of fe, fs, and has frequencies f-1, ft, f3 . f
It has an amplitude characteristic with maximum attenuation at frequencies s, f7, and infinity, and the center frequency f of each passband as shown in the figure.

, f2. ... f8, and frequencies f-1, f1 . . . that indicate the maximum value of attenuation. . . . At f7, the phase difference becomes Oo, and at all other frequencies, the phase characteristics have a phase difference such that the input/output amount phase difference is within ±90°.

Here, frequency 0< f −1< f o< f 1<
f 2 < f 3 < L < fs < fs < f7 <
fs, and the frequencies f32fo, fs''2f2 and f7=3fo.

When a filter with the characteristics shown in FIG. 4 is used, the constant oscillation frequency is f.

and set the variable frequency to f2. An oscillation circuit with f4° f6 and f8 is obtained.

Also, as shown in figure a, the frequency f3. Since f7 shows the maximum value of attenuation, frequency f3=2 f,, f7
=3 f.

From the above conditions, the constant oscillation frequency f.

2 and 3 times higher harmonics are removed, making it possible to improve the waveform of the constant oscillation frequency.

If the waveform is not improved enough by removing only the 2x and 3x harmonics, the 4x or more harmonics can also be easily removed by adding conditions similar to the above conditions to the filter characteristics. Ru.

Also, as shown in the figure, the constant oscillation frequency f.

and variable frequency f2. f4. Since there is no change in phase at f6 and f8, no change in the variable frequency band occurs by using the filter BPF of FIG.

FIG. 5 shows the amplifier AMP, power amplifier PA, and
Primary coil 11.Secondary coil 1 that constitutes the receiving antenna
This is a Nyquist diagram showing the characteristics of a conventional frequency-variable oscillation circuit consisting of mag.

When the amplifier AMP is in a saturated state, the power amplifier PA which receives the amplified output as an input is designed so as not to become saturated.

That is, this is the output side of the amplifier AMP and the power amplifier PA
It is shown that if a lossless waveform shaping circuit is connected between the input side of the power amplifier PA, a sine wave can be obtained at the output of the power amplifier PA.

Therefore, the resonant circuit shown in FIG. 1 has been used in the conventional waveform shaping circuit.

The present invention uses the filter B shown in Figure 3 as the above waveform shaping circuit.
FIG. 7 shows a block diagram in which a filter BPF is connected between an amplifier AMP and a power amplifier PA.

Further, the Nyquist diagram of the circuit shown in FIG. 8 is shown by a solid line in FIG.

It is assumed that the diagram indicated by a dotted line in the figure is equivalent to the Nyquist diagram of the circuit of FIG. 6 shown in FIG.

Assuming that there is no pass loss at the center frequency of each pass band of the filter BPF, as shown in the characteristic diagram of FIG. 4, the frequency f.

, f2. f4. Since the phase difference between the input and output amounts at f6 and f8 is 0°, the solid line and dotted line in FIG. 8 match at each of the frequencies.

Note that the assumption of no loss can be practically realized by changing the amplification degree of the amplifier AMP or the power amplifier PA, so it is not just an assumption but a valid one.

Moreover, in FIG. 8, the frequency f.

-f2. The Nyquist diagram rotates once between each of f2 to f4, f4 to f, and f6 to f8.

This is because the input/output phase difference of the filter BPF changes by 180° between these frequencies.

Furthermore, in Figure 8, the Nyquist diagram near the origin where the real and imaginary axes intersect is not clear even when measured, but if we estimate the worst case where the Nyquist diagram rotates once with the origin inside, , the frequency f in the positive part of the real axis.

1. f 02. f oa and f.

Intersect at 4. This indicates that the oscillation condition is satisfied in terms of phase.

However, since the frequency at this intersection is close to the frequency indicating the attenuation pole of the filter, the loop gain of the oscillation circuit can be made sufficiently smaller than 1.

Therefore, the frequency f in terms of amplitude.

1. f 02. f03 and f. 4, the oscillation condition is not satisfied.

Therefore the frequency f. Constant oscillation occurs.

As described in the above embodiments, the present invention uses a filter with the characteristics shown in FIG. 4 in a variable frequency oscillation circuit to widen the variable frequency band, and furthermore, the waveform of the constant oscillation frequency signal is This has a remarkable effect on improvement.

[Brief explanation of drawings]

Figure 1 is an amplifier circuit diagram with a conventional resonant circuit for waveform improvement in an oscillator circuit for information transmission in vehicles such as trains, Figure 2a is an amplitude characteristic diagram of the same circuit, and Figure 2 is the input/output of the same circuit. Figure 3 is a diagram of the filter circuit configuration according to an embodiment of the present invention, Figure 4a is an amplitude characteristic diagram of the same filter, Figure 4 is a diagram of the input/output phase difference characteristic of the same filter, and Figure 5 is a diagram of the input/output phase difference characteristic of the same filter. Figure 6 is a Nyquist diagram of the circuit shown in Figure 6. Figure 6 is a block diagram of an automatic train stopping device using a conventional variable frequency oscillation circuit.
The figure is a block diagram of an automatic train stopping device using a variable frequency oscillation circuit according to the present invention, and FIG. 8 is a Nyquist diagram of the improved circuit. BPF...Filter, AMP...Amplifier, PA...Power amplifier, 11...Receiving antenna primary coil, 12...Receiving antenna Secondary coil.

Claims (1)

[Scope of utility model registration request] A level limiting amplifier and a power amplifier having phase characteristics are connected in cascade, and a part of the output of the power amplifier is sent to the level limiting amplifier via two loosely coupled coils of a receiving antenna on the vehicle. An oscillation circuit that oscillates at a constant constant oscillation frequency is configured by positive feedback to the input side, and when the receiving antenna faces a resonant circuit that is a ground element having a frequency different from the constant oscillation frequency, the constant oscillation frequency changes. In the variable frequency oscillation circuit, the frequency is changed in the direction of the resonant frequency of the resonant circuit, and between the level limiting amplifier and the power amplifier, there is provided a frequency-changing oscillation circuit in the vicinity of the constant oscillation frequency and the changing frequency. A vehicle such as a train, characterized in that a filter is inserted therein, which has a pass band, has a maximum value of amplitude attenuation in the high frequency band of the constant oscillation frequency, and has characteristics such that the phase difference between input and output is within ±90°. Oscillation circuit for information transmission.