JPH03183205A - Limiter circuit - Google Patents

Abstract

PURPOSE:To prevent the variation of the phase of an output signal due to temperature change, etc., by providing a broad band pass filter, a variable attenuator, and a phase detector, and detecting phase change by the phase detector, and controlling the variable attenuator by its output, and vector- synthesizing together with its output signal. CONSTITUTION:An input signal is inputted to a 90 deg. hybrid 8, and a narrow band pass filter 1 and the variable attenuator 4 are connected to the 0 deg.-output of the hybrid. Then, vector synthesis with the output signal of the broad band pass filter 3 connected to the 90 deg.-output of the hybrid is executed. When an output phase varies because of the temperature change. etc., of the narrow band pass filter 1, this change is detected by the phase detector 6, and the variable attenuator 4 is controlled by its signal. Then, the phase change of the vector-synthesized output signal is eliminated. Thus, in the case of the large variation quantity of ambient temperature, the output of constant amplitude free from the phase variation between the input and the output signals can be obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to preventing the limiter output phase from changing due to temperature fluctuations or aging deterioration of a passive bandpass filter in a tank limiter circuit. be.

[Prior Art] FIG. 5 shows the configuration of a conventional tank limiter circuit. In the figure, (1) is a narrowband bandpass filter that extracts a signal of the desired frequency from the input signal, and (2)
is an amplitude limiter that limits the amplitude of the extracted signal to a constant value.

Further, (a) in FIG. 6 shows the amplitude characteristics of the narrowband bandpass filter, and (b) in the same figure shows the phase characteristics.

The signal input to the narrowband bandpass filter (1) is
Due to the filter characteristics, only the signal of the desired frequency is extracted,
The amplitude of the signal is limited by an amplitude limiter (2) and output as a signal with a constant amplitude.

[Problem to be Solved by the Invention J] In the conventional tank limiter circuit, due to changes in the ambient temperature of the narrowband bandpass filter and deterioration of the bandpass filter over time, the bandpass filter shown in FIGS. The center frequency (fo) of the output signal changes, resulting in a change in the phase difference between the human output signals shown in FIG. 5, which has the drawback of adversely affecting other circuit parts operated by the output signal.

In order to solve the above-mentioned problems, this invention adds a wide band pass filter, a variable attenuator, and a 9-phase detector, detects a phase change with the 9-phase detector, and controls the variable attenuator using the signal. The purpose is to restore the phase of the output signal, which has fluctuated due to temperature changes, etc., to its original state by vector-combining the output signal.

[Means for Solving the Problems] The limiter circuit according to the present invention inputs an input signal to a 90" hybrid, connects a narrowband bandpass filter and a variable attenuator to the 06 output of the hybrid, and connects it to the 90° output. If the phase of the two outputs changes due to temperature changes of the narrowband bandpass filter, the change is detected by a phase detector, and the signal is used to detect the change in the variable attenuator. is controlled to eliminate phase changes in the vector-combined output signal.

[Operation 1] The limiter circuit according to the present invention uses a phase detector to detect a change in the phase of the output signal when an external factor such as the ambient temperature of the bandpass filter changes.

The variable attenuator is controlled by this signal, and vector synthesis acts to eliminate phase changes in the output signal.

[Example] FIG. 1 shows an example of the present invention. (11-(2)
is the same as in FIG.

(3) is a wideband bandpass filter, (4) is a variable attenuator, (5) is a synthesizer, and (6) is a phase detector.

(7) is a low-pass filter to extract only the control signal from the output signal of the phase detector, and (8) is the input signal 06 and 9.
It is a 90° hybrid that is divided into 0° phases.

Further, FIG. 2 shows a vector synthesis state in a normal state in the circuit of FIG. 1. (9) shows the input signal of the 90' hybrid (8) in FIG. 1, (10) shows the output signal of the variable attenuator, and (Ill shows the output signal of the combiner (5)).

φ1 in FIG. 2 indicates the phase difference between the input and output signals in FIG.

When the ambient temperature, etc. of a narrow band filter (1) having a required bandwidth changes, its pass band characteristics are as follows.

When the center frequency (fo) shown in Figures 6 (a) and (b) changes and the input signal frequency in Figure 1 remains constant, the phase of the output signal of the narrowband bandpass filter (1) changes. , V shown in FIG. 2 variable attenuators (4)
The output signal of the 90" hybrid (8) and the vector composite signal on the 90° output side of the 90" hybrid (8) change to the phase of φ2 shown in Fig. 3.This phase change is detected by the phase detector (6), and the signal By controlling the amount of attenuation of the attenuator (4) and automatically controlling the output amplitude of the variable attenuator so that the phase of the vector composite signal becomes φ1 as shown in Fig. 2, the phase difference of the human output signal shown in Fig. 1 changes. Eliminate.

Although the output signal of the synthesizer (5) fluctuates by controlling the variable attenuator, the output signal has a constant output amplitude due to the amplitude limiter (2). Further, the bandwidth of the broadband bandpass filter is set to be sufficiently wide so as to be sufficiently smaller than that of the narrowband bandpass filter whose phase fluctuates due to temperature fluctuations and the like.

In the above embodiment, a variable attenuator (4) is provided, but any device may be used as long as it can change the amplitude. In addition, although 90' hybrid (8) was used in the example, 0°, 90°
If it can be divided into phases of 1, for example 90
°A distributor may also be used.

[Effects of the Invention] As described above, the present invention has the effect that when the amount of fluctuation in the ambient temperature is large, an output with a constant amplitude without phase fluctuation between input and output signals can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a limiter circuit showing an embodiment of the present invention, FIGS. 2 to 4 are diagrams showing states of vector synthesis in FIG. 1, and FIG. 5 is a block diagram of a conventional limiter circuit. 6(a) is a diagram showing the amplitude characteristics of the bandpass filter, and FIG. 6(b) is a diagram showing the phase characteristics. (1) is a narrowband bandpass filter, (2) is an amplitude controller, (3) is a wideband bandpass filter, (4) is a variable attenuator, (5) is a synthesizer, (6) is a phase detector, (7)
is a low-pass filter, (8) is a 90° hybrid, (
9) to (11) indicate output signal vectors of each section in FIG. In FIG. 1, the same or corresponding parts are designated by the same reference numerals.

Claims (1)

[Claims] In a tank limiter circuit that extracts a specific carrier wave using a passive bandpass filter and limits the output signal to a constant value, there is a hybrid circuit that outputs a signal with a phase difference of 90 degrees from the input signal, and a narrow limiter circuit that is connected to the hybrid's 0 degree output. A phase detector that compares the phases of the output signals of the broadband bandpass filter and variable attenuator, and the broadband bandpass filter connected to the 90° output of the hybrid, and the variable attenuator is controlled by the output signal thereof, The output signal of the narrowband bandpass filter side and the output signal of the wideband bandpass filter side are vector-synthesized, and the amplitude is limited by an amplitude limiter.The output phase changes due to temperature changes or aging of the narrowband bandpass filter. A limiter circuit characterized in that it is configured so that it does not occur.