JP2575312B2 - Reflection image display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application field] The present invention relates to a reflected image display device that measures the distance to a target from a reflected image pulse from the target using radio waves, ultrasonic waves, or the like.

[Conventional technology]

Hereinafter, a case of a radar mainly using radio waves will be described. FIG. 2 is a schematic configuration diagram of a radar, wherein 1 is an antenna, 2 is a transceiver, and a radar video signal, which is an intermediate frequency output of the transceiver 2, is an FTC (First Time Constan
t) A differential circuit called a circuit 3 removes the influence of rain, snow, etc., and inputs the result to a video pulse width expansion circuit 4. The video pulse width expansion circuit 4 comprises a low-pass filter and an amplifier.
The noise is removed to form a smooth pulse waveform, which is convenient for digital signal conversion at the next stage. In the digital signal conversion, for example, a high-speed parallel comparison type A / D converter is used as the A / D converter 5, and the converted digital signal is sampled by a sampling circuit 6 in the next stage. Store in the cell specified in 7A. The contents of the video memory 7 are transmitted to the CRT display unit 9 via the parallel / parallel conversion circuit 8. The CRT display unit 9 is displayed by raster scanning, and when the origin is at the center, the captured signal is displayed at 200 to 400 dots in the radial direction by the above-described sampling.

[Problems to be solved by the invention]

Now, it is assumed that a CRT with normal accuracy is used, and the number of effective scanning lines is 400. Assuming that the maximum ranging distance (corresponding to the maximum value that can be represented on the CRT display) is 1 mile, this is 12.34 μs in terms of time. If the origin is the center of the CRT display, video dots appear within 200 scanning lines. The dot interval is 0.061 μs (= 12.34 μs / 200) in time.
Assuming a maximum ranging distance of 16 miles, 197.44μ in time
s, the dot interval is 0.987 μs.

Incidentally, in FIG. 2, the time interval between sampling the reflected video pulse after A / D conversion by the sampling circuit 6 and taking it into the video memory 7 is equal to the dot interval time appearing in the CRT display. Therefore, if the maximum distance is changed, the sampling period must be changed. In the above example, 0.061 when the maximum distance is 1 mile
μs and 0.987 μs for 16 miles. In the case of radar, for example, the transmitter has a repetition frequency of 2 kHz and a pulse width of 500 n
Generates about s transmission pulses. The reflected image pulse also has a minimum pulse width of this extent. Therefore, when the maximum distance is increased, the reflected image pulse may not be sampled depending on the sampling period. For example
500 ns with a sampling period of 0.987 μs at 16 miles
In some cases, a pulse having a width of (0.5 μs) cannot be detected.
If the maximum distance is further increased, it becomes almost impossible.

Conventionally, as a countermeasure, an image pulse width expanding circuit 4 for expanding the width of a reflected image pulse is provided in a stage preceding the A / D converter 5 as shown in FIG. This circuit removes the nozzle,
At the same time as smoothing the pulse waveform, the low-pass filter makes the rising and falling edges of the pulse waveform gradual, and the pulse width is substantially widened. And However, at the same time, the phase transition becomes large, which is not suitable for accurate distance measurement.

In view of the above circumstances, an object of the present invention is to provide a reflection image display device that adjusts a pulse width of a reflection image pulse in accordance with a change in a sampling period in accordance with a change in a maximum distance measurement distance.

[Means for solving the problem]

The reflection image display device of the present invention samples the reflection image pulse and changes the sampling period taken in the video memory. The reflection image pulse is sequentially passed through a low-pass filter and a peak holder circuit, and is applied to the trailing edge of the pulse waveform. Means for changing the effective time constant to change the length of the wave tail of the pulse waveform.

[Action]

The circuit consisting of the low-pass filter and the peak holder circuit is configured so that the time constants at the leading edge and the trailing edge of the incident reflected image pulse are different from each other, and the time constant at the trailing edge determines the maximum distance measurement distance. When you change, change it accordingly. As a result, the pulse width of the reflected video pulse can be effectively increased in a case where the maximum distance measurement distance is 16 miles and the sampling time is 0.987 μs as described above.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings. The configuration of the radar is exactly the same as that of FIG. 2, but the configuration of the video pulse width expanding circuit 4A is different as described later. To change the maximum distance, the programmable frequency divider 6B is changed to change the sampling period, and the trailing edge of the pulse waveform is extended in the video pulse width expansion circuit 4A in accordance with the change in the sampling period.

FIG. 1 shows a wiring diagram of one embodiment of the video pulse width expansion circuit 4A. In this figure, the waveforms at the points indicated by L, M, and N are shown later. The low pass filter 11 extends from the input terminal 10 to the point L, the peak holder circuit 12 extends from the point L to the point M, and the point M The buffer 13 is from point N to point N. L, M, although demarcation N is not critical, the low-pass filter 11 is divided almost so, and a CR circuit and a transistor Q ₁ Tokyo. Transistor Q ₁ is the emitter follower operation, the filter characteristics are determined by the combination of the plurality of resistors, capacitors, carried out the removal of high frequency noise, the amplification of the video reflected pulse in this circuit. Next peak holder circuit 12 charges the capacitor C ₀ based on the input image reflected pulse, the circuit for performing peak hold, following the polarity of the output voltage inverted by the transistor Q ₂ to which is controlled by the voltage of the capacitor C ₀ It is sent to the buffer 13 of the stage. Since the circuit of FIG. 1 is a video reflection pulse input is a negative polarity transistor Q ₂
Uses an n-type junction FET. C ₁ of the input stage of the peak holder circuit 12 has a sufficiently large value coupling capacitor may substantially as conducting the pulse. A
The circuit components from point to point B are provided to change the time constant, thereby extending the wave tail of the image reflection pulse. The changeover switches 121 and 122 perform switching to change an appropriate time constant when changing the maximum distance measurement distance. Changes in the waveforms at points L, M, and N due to such adjustment switching are shown in FIG. 3 and thereafter, but a general description will be given here.

In the case of a short distance, there is no need to particularly greatly increase the pulse width.
22 is the f side. The f side is open. The time constant of the charging and discharging of the capacitor C ₀ is just due to the difference of the charge and discharge current path Condesa C _0, not intended to particularly prolong pulse trailing edge. That is, the negative reflected video pulse is
When applied to 10, at its falling to delayed little time and falling, cracking negative pulse table L point, immediately charges capacitor C _0, it produces a positive pulse voltage to the M point. When the input negative pulse rises, the transistor Q ₁ is operated, the negative charges charged in the capacitor C _0, through Torajisuta Q _1, is discharged.

In the case of the middle distance and the long distance, the time constant that effectively operates with respect to the trailing edge of the reflected image pulse is changed. Therefore, the changeover switch 121 is set to the e side, and the changeover switch 122 is set to the g side or the h side. g side, the resistor R _1, R ₂ is connected to the h side, R ₁
Small, switched as R ₂ large middle distance, in the long distance.

When a negative reflected image pulse is applied to the input terminal 10,
State capacitor C ₀ by a pulse leading edge or pulse fall is charged is almost the same because the resistance R _1, R ₂ is high relative to the impedance of the resistor R and the short distance. However, the rise of the pulse, the diode D ₂ is so would cut off the discharge current path by a transistor to Q ₁ case of short distance, discharge line of the rope only through resistor R _1, or R _2. That is, the rising time constants are completely different, and the resistances R ₁ and R ₂
By taking large, the length of the wave tail can be made sufficiently large.

Next, FIGS. 3 to 5 show the operation of the embodiment in which the distance is changed in three stages from a short distance to a long distance. These figures show a part of the input waveform and each waveform at each point of L, M, and N. FIG. 3 shows a case where the distance is short, and the maximum distance to be measured is 1/2 mile. In time, it is 6.17 μs,
Assuming that the number of scanning lines is N, the sampling frequency f _S is f _SO = N
/6.17μs. As in the previous example, if N = 200,
f _S = 32 MHz, and the sampling period is 0.031 μs. At this time, the changeover switch 121 is set to the d side, and the changeover switch 122 is set to the f side (no connection). The waveform at the point N only reverses the polarity of the waveform at the point M. Rise of the waveform of the M points SadaMari primarily by the characteristics of the low-pass filter 11, falling is determined by the time constant of the discharging of the transistor Q _1.

FIG. 4 shows a case where the maximum distance is set to 4 miles (49.36 μs in terms of time) when the distance is medium and the sampling frequency is 1 / 8f _SO and the sampling period is
0.248 μs. Changeover switch 121 is tilted in e side, cut off the current path during discharge of the capacitor C ₀ the diode D _2, to discharge changeover switch 122 through a resistor R ₁ by the g side. Since the wave tail is extended as seen in the waveforms at the points M and N, about five sample points can be collected during the pulse period.
Fig. 5 shows the case of long distance, and the maximum ranging distance is 32 miles (39
In this case, the sampling frequency is 1/64 f _SO and the sampling period is 1.98 μs. Unless according to the present invention, sampling data cannot be normally collected, but in this embodiment, about two sampling points can be collected.

〔The invention's effect〕

In radar, etc., in order to display the reflected video pulse from the target on the CRT, the data is sampled after A / D conversion and the data is loaded into the video RAM.The sampling period depends on whether the target is near or far. Change and sample. On the other hand, since the pulse width of the transmission pulse is constant at about 500 ns, it may not be possible to collect sampling data within a pulse width of the reflected image pulse for a target at a long distance. The circuit placed before the A / D converter, which is called a conventional video pulse width expansion circuit, is mainly composed of a low-pass filter, the pulse width is fixed, and the pulse width is fixed to a small extent. The main effect was the decrease. If an attempt is made to increase the pulse width, there is a phase delay and an error occurs.

On the other hand, according to the present invention, the time constant of the trailing edge and the leading edge of the reflected image pulse operate completely differently, and the time constant of the trailing edge can be changed when the maximum distance measurement distance is changed. . As a result, the width of the reflected image pulse is expanded, and the sampling point can be collected even at a long distance. On the other hand, since the time constant of the leading edge can be made sufficiently small, no error occurs due to the time delay of the leading edge.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, FIG. 2 is an overall block diagram of a radar, FIG. 3, FIG. 4, and FIG.
FIG. 2 is a diagram showing input waveforms and waveforms at respective points of the circuit of FIG. 1 in the case of a middle distance and a long distance in the embodiment. 2 ... Transceiver, 3 ... FTC circuit, 4,4A ... Video pulse width expansion circuit, 5 ... A / D converter, 6 ... Sampling circuit, 7 ... Video memory, 9 ... CRT display unit , 11 ... Low-pass filter, 12 ... Peak holder circuit, 13 ... Buffer, 121,122 ... Changeover switch.

Claims (1)

(57) [Claims] An apparatus for receiving a reflected pulse from a target of a transmission pulse and displaying a reflected image pulse in accordance with a distance from the target, wherein the reflected image pulse is sampled,
A means for changing the sampling period taken into the video memory, and a reflected image pulse are sequentially passed through a low-pass filter and a peak holder circuit to change the time constant effective only for the trailing edge of the pulse waveform, thereby obtaining a pulse waveform. Means for changing the length of the tail, and according to the distance of the target, when the maximum distance measurement distance that can be displayed is changed, waveform sampling data can be reliably collected. Reflective image display device