JP3243523B2 - Synchronous ripple elimination circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an FM / CW system using a triangular wave for frequency modulation (frequency modulation / continuous wave system).
And a synchronous ripple elimination circuit for synchronizing a ripple of a beat signal generated at a discontinuous point of the modulated wave with a vertex of the modulated wave and removing the ripple for a certain period of time.

[0002]

2. Description of the Related Art A radio altimeter, which is a kind of a conventional distance measuring device, generally uses an FM / FM using a triangular wave for modulating a carrier wave.
By using the CW method, the distance to the target can be measured even in a stationary state. This simple principle will be described with reference to FIG. In FIG. 3, reference numeral 6 denotes a driver circuit, which is a circuit for generating a triangular wave for frequency modulation. 5 is a voltage controlled oscillator (VCO: Voltage)
Control Oscillator), which is an element that converts a triangular wave voltage signal output from the driver circuit 6 into a frequency. Reference numeral 4 denotes a coupler, which is an element for splitting a signal from the voltage controlled oscillator 5. Reference numeral 3 denotes a circulator, which transmits an output from the coupler 4 to the antenna 2 and outputs a signal received from the antenna 2 to the mixer 7. Reference numeral 2 denotes an antenna, which is a drive signal from the circulator 3 (a carrier signal frequency-modulated by a triangular wave).
Is emitted as an antenna A, and a reflection signal reflected upon the target 1 is received as an antenna B.

[0003] The mixer 7 receives a signal (Re) from the coupler 4.
And a signal (Lo) from the circulator 3 and an element for outputting an intermediate frequency signal (IF signal). 8
Is a high-order BPF (Band Pass Filter). By setting an appropriate cutoff frequency, unnecessary frequency components can be removed to obtain a target beat frequency (frequency difference between the drive signal and the reflected signal). . By analyzing the frequency components of the beat signal, information on the distance to the target can be obtained.

[0004]

However, in the high-order BPF 8 described above, the discontinuous point of the triangular wave of modulation (switching from monotonically increasing to monotonically decreasing or monotonically decreasing to monotonically increasing) due to its steep attenuation characteristic. A transient phenomenon occurs due to a sudden change due to point (1), and ripples are superimposed on most of the required beat signals. Obviously, this would make it difficult to obtain the information necessary for the radio altimeter given as an example.

The present invention has been made in such a situation, and an object of the present invention is to provide a synchronous ripple removing circuit capable of removing ripple from a beat signal in synchronization with a triangular wave for modulation.

[0006] Other objects and novel features of the present invention will be clarified in embodiments described later.

[0007]

In order to achieve the above object, the present invention provides a synchronous ripple elimination circuit provided in an FM / CW distance measuring apparatus using a triangular wave for modulation, wherein the synchronous ripple elimination circuit is provided. A vertex detection circuit that detects a vertex and outputs a synchronization signal, a pulse generation circuit that generates a pulse signal based on the synchronization signal from the vertex detection circuit and outputs a fixed delay time, and a mixer signal of the distance measurement device. -Order HPF that separates modulated wave and signal wave to remove modulated wave component
And a high- order BPF, and a gate circuit inserted between the low-order HPF and the high-order BPF to limit passing or non-passing of an output signal from the low-order HPF according to a signal level of the pulse generation circuit. The gate circuit is characterized in that an output signal from the low-order HPF is not passed in synchronization with the pulse signal within the predetermined delay time with respect to the synchronization signal.

[0008]

[0009]

[0010]

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a synchronous ripple elimination circuit according to the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a distance measuring device including a synchronous ripple elimination circuit. A dotted line indicates a synchronous ripple elimination circuit 9. In this figure, reference numeral 10 denotes a vertex detection circuit, which is for frequency modulation output from the driver 6 in FIG.
A vertex of a triangular wave as shown in FIG. 3A is detected, and a synchronization signal shown in FIG. 11 is a low-order HPF (High Pass Filte
r) is a secondary HPF, which discriminates the frequency of an IF signal (including a modulation wave component and a beat signal component) from the mixer 7 and removes unnecessary low frequency frequency components (modulation wave components) from the IF signal. The signal is removed by a gradual attenuation characteristic and a required high-frequency component (beat signal component) is output. Reference numeral 13 denotes a pulse generation circuit which outputs pulse signals at regular intervals as shown in FIG. The rise of the pulse signal coincides with the synchronization signal (that is, synchronizes with the top of the triangular wave) and falls after a certain delay time, and has a pulse width from the arrival of the synchronization signal to the certain delay time. Reference numeral 12 denotes a gate circuit which synchronizes a ripple component (harmonic) contained in a high-frequency signal output from the secondary HPF 11 with a pulse signal output from the pulse generation circuit 13, cuts the pulse component (non-passage), and outputs the gate circuit. Is input to the high-order BPF 8.
The gate circuit 12 performs passing / non-passing operations at fixed time intervals in synchronization with the pulse signal.
In the period corresponding to the pulse width of the pulse signal, the gate circuit 12 operates so as not to pass as shown in FIG.

The other structure is the same as that of the conventional distance measuring apparatus shown in FIG. 3, and the same or corresponding parts are denoted by the same reference characters and description thereof is omitted.

The second-order HPF 11 exhibits a moderate attenuation characteristic as compared with the high-order BPF 8, and the ripple component appears as a narrow pulse in which the ripple component is easily removed as compared with a case where the mixer signal is directly input to the high-order BPF 8. . Therefore, by making the gate circuit 12 in the non-passing state for a predetermined time width in synchronization with the apex of the triangular wave as described above, the output of the gate circuit becomes such that the ripple component is removed in synchronization with the apex of the triangular wave. By inputting the gate circuit output to the high-order BPF 8, the beat signal (the signal of the frequency difference between the drive signal and the reflection signal) is obtained even if the high-order BPF 8 performs a sharp band limitation.
Can be obtained as a constant value.

As described above, according to the present embodiment, FIG.
By inserting the synchronous ripple elimination circuit 9 shown in the dotted line in FIG. 1 between the mixer 7 and the high-order BPF 8 of the conventional radio altimeter shown in FIG.

Here, the low-order HPF means first-order to third-order HPF, and the high-order BPF means fourth-order or higher BPF.
Shall mean. In the experiments of the inventor, the low-order HPF
The best results are obtained with the secondary HPF exemplified in the embodiment.

Although the embodiments of the present invention have been described above, it is obvious to those skilled in the art that the present invention is not limited to the embodiments and that various modifications and changes can be made within the scope of the claims. There will be.

[0018]

As described above, according to the present invention,
In an FM / CW distance measuring apparatus using a triangular wave for frequency modulation of a carrier, a vertex detecting circuit for detecting a vertex of the triangular wave and outputting a synchronizing signal; A pulse generating circuit for generating and outputting a fixed delay time, and a low-order HPF for separating a modulated wave and a signal wave from a mixer signal and removing a modulated wave component
And a high- order BPF, and a gate circuit inserted between the low-order HPF and the high-order BPF to limit passing or non-passing of an output signal from the low-order HPF according to a signal level of the pulse generation circuit. The gate circuit includes a frequency difference between the drive signal and the reflection signal by making the output signal from the low-order HPF non-passing in synchronization with the pulse signal within the predetermined delay time with respect to the synchronization signal. There is an effect that ripples at the time of detecting a beat signal can be reliably removed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a distance measuring device according to an embodiment of the present invention, including a synchronous ripple elimination circuit.

FIG. 2 is a waveform chart for explaining the operation of the embodiment.

FIG. 3 is a basic block diagram of a radio altimeter as a conventional distance measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Target 2 Antenna 3 Circulator 4 Coupler 5 Voltage controlled oscillator 6 Driver 7 Mixer 8 Higher order BPF 9 Synchronous ripple elimination circuit 10 Vertex detection circuit 11 Secondary HPF 12 Gate circuit 13 Pulse generation circuit

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-103394 (JP, A) JP-A-2-290582 (JP, A)

Claims (1)

(57) [Claims] 1. A synchronous ripple elimination circuit provided in an FM / CW distance measuring apparatus using a triangular wave for modulation, wherein the vertex detecting circuit detects a vertex of the triangular wave and outputs a synchronizing signal. A pulse generation circuit that generates a pulse signal by the synchronization signal from the vertex detection circuit and outputs a fixed delay time; and a low-frequency signal generator that separates a modulation wave and a signal wave from a mixer signal from the mixer signal of the distance measuring device and removes a modulation wave component. Higher order HPF and higher order BP
F and the low-order HPF inserted between the low-order HPF and the high-order BPF.
A gate circuit for restricting the output signal from F from passing or non-passing according to the signal level of the pulse generation circuit, wherein the gate circuit synchronizes with the pulse signal within the fixed delay time with respect to the synchronization signal. The lower order H
A synchronous ripple elimination circuit, wherein an output signal from a PF is not passed.