JPS6126332A - Multipath distortion correcting circuit - Google Patents

Abstract

PURPOSE:To surely correct a multipath distortion, by correcting an input signal in accordance with the difference between the output signal of a low-pass filter and the signal which is the arithmetic mean of the output signals of a (+) side and (-) side envelope detecting circuits. CONSTITUTION:An adder 2 outputs the difference between an input signal (a) and correcting signal (h). The output signal (b) of the adder 2 is supplied to a low-pass filter 3, (+) side envelope detecting circuit 4, and (-) side envelope detecting circuit 5. The filter 3 outputs a signal (c), from which noise frequency components are attenuated. On the other hand, the output signals (d) and (e) of the circuits 4 and 5 are averaged by means of an adder 6 and subtractor 7 and, as a result, a signal (f) is outputted. An adder 8 outputs a signal (g) which is the difference between the signals (f) and (c). Since the signal (g) is superposed upon the signal (a) and proportional to the level of noises, the correcting signal (h) is obtained when the signal (a) is amplified at an amplifier 9. The corrected signal (b) is outputted from an output terminal 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a multipath distortion correction circuit that corrects multipath distortion.

In conventional radio receivers and the like, when multipath occurs, a signal on which noise is superimposed as shown in FIGS. 5(A) and 5(B) is output from the demodulation circuit. If noise is symmetrically superimposed on the signal, as shown in (A) of the same figure, by passing it through a low-pass filter, it is possible to obtain a signal from which the noise has been removed, as shown in (C) of the same figure. but,
If noise is asymmetrically superimposed on the signal, as shown in FIG. 5B, distortion will occur in the signal, as shown in FIG.

Problems to be Solved by the Invention The present invention is an attempt to improve the above-mentioned drawbacks, and its purpose is to make it possible to reliably correct multipath distortion. Examples will be described in detail below.

Means for Solving the Problems In order to solve the above problems, the present invention includes a first adder that outputs the difference between the input signal and the correction signal, and a cutoff frequency at the upper limit of the frequency used. a low-pass filter that receives the output signal of the first adder and also attenuates and passes frequency components higher than the cutoff frequency;
a + side envelope detection circuit that outputs a signal that sharply follows the rise of the output signal of the adder and gently follows the fall of the output signal;
Outputs of a negative envelope detection circuit, a positive envelope detection circuit, and a negative envelope detection circuit that output a signal that sharply follows the falling edge of the output signal of the first adder and gently follows the rising edge of the output signal of the first adder. an averaging means for averaging signals; a second adder for outputting the difference between the output signal of the averaging means and the output signal of the low-pass filter; and an output signal of the second adder at a predetermined amplification factor. A multipath distortion correction circuit characterized by comprising an amplifier that amplifies and outputs a correction signal.

Embodiment FIG. 1 is a block diagram of an embodiment of the present invention, in which 1 is an input terminal into which the output signal of, for example, an IF 11 unit (not shown) is input, 2 is an adder, and 3 is a resistor R1 and a capacitor. C
4 is a + side envelope detection circuit consisting of a diode DI, a capacitor C2 and resistors R2 and R3, 5 is a diode D2. Capacitor C3 and resistor 1'14. One side envelope detection circuit consisting of R5, 6 an adder, 7 a divider with a divisor of 2, 8 an adder, 9 an amplifier,
10 is an output terminal. In addition, R1= R2= R3,C
The resistance values of the resistors R1 to R3 and the resistance values of the capacitors 01 to C3 are set so that I=C2=C3.

Now, for example, the noise-superimposed signal a shown in FIG.
Assuming that no signal is applied to one terminal of a, the signal a
is the low pass filter 3. + side envelope detection circuit 4
and - will be added to the colorimetric cross-wire detection circuit 5. Assuming that the frequency component of the signal a on which noise is superimposed is as shown in FIG. Its characteristics are set so that the signal is attenuated and passed through, so the output signal C of the low-pass filter 3 is a signal obtained by dulling the noise superimposed on the signal a, as shown in Fig. 2 (B). becomes. Also, +
Since the side envelope detection circuit 4 charges the capacitor C2 via the diode D1 and the resistor R2, and discharges the charge of the capacitor C2 via the resistor R2, its output signal d is as shown in FIG. As shown, the rise is steep and the fall is gradual. Also, -Example line detection circuit 5
charges the capacitor c3 via the resistor R4, and discharges the charged charge via the diode D2 and the resistor R4, so the output signal e has a steep fall and a rise as shown in (D) of the same figure. becomes gradual.

Then, the output signals d and e of the + side envelope detection circuit 4 and the - colorimetric cross detection circuit 5 are added in an adder 6 and added to a divider 7, and the output signals from the divider 7 are shown in FIG. 2(E). A signal f shown is output. The adder 8 outputs a signal g indicating the difference between the output signal f of the divider 7 and the output signal C of the low-pass filter 3. Here, the output signal g of the adder 8 is proportional to the level of noise superimposed on the signal a, as shown in FIG. By applying the output signal of 9 to one terminal of the adder 2, the output signal of the adder 2 becomes one from which noise has been removed.

In addition, in FIGS. 4(A) to 4(F), a signal having a higher frequency than the signal a shown in FIG. 2(A) and on which no noise is superimposed is filtered by the low-pass filter 3, and the + side envelope This shows the waveforms c to g of each part when added to the detection circuit 4 and the colorimetric circuit detection circuit 5, and as shown in (F) in the same figure, the level of the output signal g of the adder 8 is zero. Therefore, even if a signal a having a high frequency and no noise is superimposed is applied to the input terminal 1, there will be no malfunction.

DETAILED DESCRIPTION OF THE INVENTION As described above, the present invention includes: a first adder such as adder 2 that outputs the difference between an input signal and a correction signal; a low-pass filter that filters the output signal of the first adder; a + side envelope detection circuit which receives the output signal of the first adder;
An averaging circuit consisting of an adder 6, a divider 7, etc., which averages the output signals of the one-side envelope detection circuit that inputs the output signal of the adder, the +-side envelope detection circuit, and the envelope detection circuit. a second adder such as an adder 8 for outputting the difference between the output signal of the averaging means and the output signal of the low-pass filter;
Since it is equipped with an amplifier that amplifies the output signal of the adder by a predetermined amplification factor and outputs a correction signal, it has the advantage that multipath distortion can be corrected.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of the operation of Fig. 1, Fig. 3 is a characteristic diagram of the low-pass filter, Fig. 4 is an explanatory diagram of the operation of Fig. 1, Fig. 5 is a waveform diagram for explaining the conventional drawbacks. 1 is an input terminal, 2, 6.8 is an adder, 3 is a low-pass filter, 4 is a + side envelope detection circuit, 5 is also a one side envelope detection circuit, 7 is a divider, 9 is an amplifier, 10 is an output It is a terminal. Patent Applicant Fujitsu Ten Ltd. Representative Patent Attorney Gobe Tamamushi (1 other person) Figure 1, Figure 6, Figure 2

Claims (1)

[Claims] a first adder that outputs the difference between the input signal and the correction signal;
a low-pass filter that receives as input the output signal of the first adder, which has a cutoff frequency at the upper limit of the frequency used, and also attenuates and passes frequency components higher than the cutoff frequency; and the output signal of the first adder. a + side envelope detection circuit that outputs a signal that sharply follows the rising edge of the output signal and slowly follows the falling edge of the output signal of the first adder; a negative envelope detection circuit for outputting a signal, an averaging means for averaging the output signals of the positive envelope detection circuit and the negative envelope detection circuit, and averaging means for averaging the output signals of the averaging means and the low-pass filter. A multipath comprising: a second adder that outputs the difference between the output signal and the output signal; and an amplifier that amplifies the output signal of the second adder by a predetermined amplification factor and outputs the correction signal. Distortion correction circuit.