JP2002335129A - Fm demodulator and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an FM demodulator capable of restricting a distortion of a demodulation signal under multi-path conditions. SOLUTION: There is provided an FM demodulation means for switching a first FM demodulation operation and a second FM demodulation operation to FM-demodulate a reception signal, and between the first FM demodulation operation and the second FM demodulation operation, responses to the amplitude change of the reception signal in a demodulation signal to be output from the FM demodulation means are set to be different.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for receiving a frequency-modulated carrier and demodulating the carrier using digital signal processing, and more particularly to a receiver excellent in a function of suppressing multipath distortion.

[0002]

2. Description of the Related Art Here, frequency modulation (frequency modula
(hereinafter, referred to as FM modulation) is a modulation method in which the frequency of a carrier is changed in proportion to the size of a signal to be transmitted. Hereinafter, a signal to be transmitted is a modulating signal, and a carrier wave that is FM-modulated by the modulating signal is an FM wave (frequency modulated wave).
Demodulation for extracting a modulation signal from a wave is referred to as FM demodulation (frequency d
emodulation), and the modulated signal extracted by FM demodulation is referred to as a demodulated signal.

[0003] First, the principle of FM demodulation will be briefly described. In the FM wave, the frequency change of the carrier is proportional to the amplitude change of the modulation signal. Therefore, in order to extract a modulated signal, that is, a demodulated signal from an FM wave, an FM demodulator satisfying the following conditions is required. The amplitude of the output signal changes in response to a change in the frequency of the input FM signal. The amplitude of the output signal does not respond to the change in the amplitude of the input FM signal. Note that there are various conditions required for the FM demodulator other than those described above and above, but the description is omitted here for simplicity.

FIG. 9 is a schematic diagram illustrating a conventional FM demodulator that satisfies the above conditions and at the same time. In the figure, 9 is an FM demodulator, 20 is a demodulation unit, 21 is an amplitude detection unit, 22 is a correction coefficient calculation unit, and 23 is an amplitude correction unit.
The operation will be described. Demodulator 20 demodulates input signal x0 and outputs output signal y0. This output signal y0 satisfies the above condition, but does not satisfy the above condition. That is, the output signal y0 includes a response component to an amplitude change of the input signal x0 (hereinafter, referred to as an amplitude change response component).

The amplitude corrector 23 removes such an amplitude change response component from y0. First, the amplitude detector 21 detects the amplitude z0 of the input signal x0 and outputs the detected signal to the correction coefficient calculator 22. The correction coefficient calculator 22 outputs a correction coefficient z1 for canceling the amplitude change response component included in the output signal y0 based on the input amplitude z0. The amplitude correction unit 23 removes the amplitude change response component from the output signal y0 by multiplying the output signal y0 of the demodulation unit 20 and the output coefficient z1 of the correction coefficient calculation unit 22, and almost satisfies the above conditions and Output as demodulated signal y1.

Hereinafter, such a conventional FM demodulator will be described in more detail. FIG. 10 is a configuration diagram illustrating a receiver having a conventional FM demodulator. Here, a configuration of an FM audio broadcast receiver is illustrated. In the figure, 1 is an antenna, 2 is an RF amplifier, 3 is a frequency converter, 4 is a local oscillator, 5 is an intermediate frequency filter, 6 is a limiter intermediate frequency amplifier, 7 is a pre-filter, 8 is an AD converter, 9 is The FM demodulator 10 shown in FIG. 9 is a DA converter, 11 is an audio amplifier, and 12 is a speaker.

The operation will be described. The FM wave received by the antenna 1 is amplified by the RF amplifier 2, then frequency-converted by the frequency converter 3, and
Unnecessary components such as adjacent channel waves are removed. The FM wave that has passed through the intermediate frequency filter 5 is subjected to amplification amplitude limitation by a limiter intermediate frequency amplifier 6, after which intermediate frequency harmonic components are removed by a pre-filter 7, and converted into a digital signal by an AD converter 8. Is converted. Digitally converted FM
After the wave is demodulated by the FM demodulator 9, the wave is converted to an analog audio signal by the DA converter 10 and output to the speaker 12 via the audio amplifier 11.

FIG. 11 is a configuration diagram illustrating details of the FM demodulator 9 shown in FIG. 9 and FIG. The FM demodulator 9 is, for example, a quadrature type demodulation circuit, and includes a demodulation unit 20, an amplitude detection unit 21, a correction coefficient calculation unit 22, and an amplitude correction unit 23. Here, the demodulation unit 20
Is a delay unit 101, a multiplier 102, a low-pass filter 1
03. Further, the amplitude detector 21 includes a first multiplier 110, a second multiplier 111, and an adder 1
12 and a low-pass filter 113.

The operation of the demodulation unit 20 will be described. AD
The digital FM wave input from the converter 8 is converted into a signal x0 by the delay unit 101, the multiplier 102, and the multiplier 1
Input to 10. The delay unit 101 delays the input signal x0 and outputs it to the multiplier 102 as a signal x1. The multiplier 102 multiplies the output signal x1 of the delay unit 101 by the input signal x0, and uses the result of the multiplication as a signal x2 of the low-pass filter 1.
03 is output. The low-pass filter 103 includes a multiplier 102
To remove the low-frequency component from the output signal x2 and output the signal y0 to the amplitude correction unit 23.

The signals x0, x1, x2, and y0 are exemplified below by using mathematical expressions. First, assuming that the input signal x0 is x0 = A cos {w _c kT + p (kT)} (1), the output signal x1 of the delay unit 101 is x1 = A sin {w _c kT + p ( (k-1) T)} (2) Here, A is the amplitude of the input FM wave, w _c is F
The angular frequency of the carrier of the M wave, k is an arbitrary integer, and T is FIG.
Is the sampling period of the AD converter 8 and p (kT) is the amount of phase shift at time kT. Also, w _c T = Nπ / 2
(N = 1).

The output signal x2 of the multiplier 102 is a signal
the product of x0 and signals x1, x2 = x0 · x1 = A 2 sin {p (kT) - p ((k - 1) T)} / 2 + A 2 sin {4 w c kT + p (kT) + p ((k-1) T)} (3) The output signal y0 of the low-pass filter 103 is a signal
x2 is a low-pass formed by removing the contents ^{signal, y0 = A 2 sin {p} (kT) - p ((k - 1) T)} / 2 ≒ A 2 T dp / dt / 2 ··· (4 ). t is time (continuous time system).

Here, dp / dt included in equation (4) is a time derivative of the amount of phase shift, and this dp / dt is a modulation signal (ie, a demodulated signal) to be obtained. To retrieve this dp / dt from y0 must remove the A ² is the amplitude change response component from the right side of the equation (4). The amplitude detector 21, the correction coefficient calculator 22, and the amplitude corrector 2 shown in FIG.
No. 3 removes such an amplitude change response component from y0.

The amplitude detector 21 calculates dp /
Calculate the coefficient A ² of dt. Specifically, the first multiplier 110 calculates the square of the input signal x0 and outputs the result as a signal x3. The second multiplier 111 calculates the square of the output signal x1 of the delay unit 101 and outputs the result as a signal x4. The adder 112 outputs the output signals x3 and x4 of these first and second multipliers.
And the addition result is set as a signal x5 in the low-pass filter 113.
Output to The low-pass filter 113 is connected to the adder 112
From the output signal x5, and outputs the extracted signal to the correction coefficient calculation unit 22 as a signal z0. The signal z0 is approximately the size of A ² by calculation.

The correction coefficient calculating section 22 receives the output signal z0 of the amplitude detecting section 21 and obtains a correction coefficient C ₀ / A ² which is inversely proportional to the dp / dt coefficient shown in equation (4). Here, C ₀ is an arbitrary number, for example, 2 / T. The correction coefficient calculation unit 22
The obtained correction coefficient C ₀ / A ² is output to the amplitude correction unit 23 as the correction coefficient z1.

The amplitude correction unit 23 includes a correction coefficient calculation unit 2
2 outputs the correction coefficient z1 to the demodulation unit 2 shown in equation (4).
The demodulated signal y1 is obtained by multiplying the output signal y0 by 0.
In this way, demodulated, the demodulated signal y1 by the amplitude correction has been _{subjected, y1 = C 1 · dp /} dt ··· (5) , and the not vary with the amplitude of the input signal x0 amplitude A. That is, the output y0 of the demodulation unit 20 fluctuates in accordance with the amplitude A of the input signal x0 as shown on the right side of Expression (4). y1 does not vary depending on the amplitude A of the input signal x0 as shown on the right side of Expression (5). The coefficient C ₁ in formula (5) is an arbitrary number.

[0016]

The conventional FM demodulator performs FM demodulation which satisfies the conditions and the conditions described above. However, this FM demodulator can perform FM demodulation without any problem when the received FM wave is a direct wave, but the received wave is a composite wave of the direct wave and the reflected wave. Under a certain multipath situation, there is a problem that distortion (hereinafter, referred to as multipath distortion) occurs in a demodulated signal. And especially
The problem was serious in FM audio broadcasting broadcasted in the VHF band.

Here, the direct wave means a radio wave that reaches the receiver directly from the transmitter without being reflected by the ionosphere and the like, and the reflected wave is reflected by the ionosphere and structures. It means the radio wave that reaches the receiver after being performed.

Hereinafter, such multipath distortion will be described. Here, for simplicity, one direct wave and one
A case where two reflected waves are received as a combined wave by the receiver will be described.

Assuming now that the angular frequency of the direct wave is w _c and the angular frequency difference between the direct wave and the reflected wave is w _d , the direct wave is sin (w _c t),
Reflected wave can be expressed as _{r · sin {(w c +} w d) t}.
From this, the composite wave M of a direct wave to be received at the receiver the reflected waves (t) is, M (t) = sin ( w c t) + r · sin {(w c + w d) t} = sin (w _c t) + r {sin (w _c t) cos (w _d t) + cos (w _c t) sin (w _d t)} = {1 + r ・ cos (w _d t)} sin (w _c t) + sin (w _d t) cos (w _c t) = [(1 + r ・ cos (w _d t)) ² + cos (w _c t) ² ] ^1/2 sin (w _c t + φ ) = {1 + 2 r · cos (w _d t) + r ² } ^1/2 sin (w _c t + φ) (6) Here, φ = arctan [sin (w d t) / {1 + r · cos (w d t)}] is (7). Also, r is the amplitude of the reflected wave, and the amplitude of the direct wave is set to 1 for convenience. Actually, both w _c and w _d temporally change due to the FM modulation, but here, it is assumed that they take a substantially constant value in a short time when multipath distortion occurs. The angular frequency difference w _d is mainly due to the propagation time difference and FM modulation.

Since the demodulated signal y1 output from the amplitude corrector 23 in the conventional FM demodulator shown in FIG. 11 is the time derivative of the phase component of the input signal x0 as shown in equation (5), demodulated signal signal x0 is obtained by demodulating the case of the above composite wave M (t) y1, from equation (7), y1 = dφ / dt = - r · w d {r + cos (w d t) } / {1 + 2 r cos (w _d t) + r ² } (8) Here, the coefficient C1 shown in Expression (5) is set to ₁ for convenience.

Here, since it is assumed that the values of w _c and w _d are constant over time, the temporal variation of dφ / dt shown in equation (8) is the multipath distortion. FIG. 12 is a diagram illustrating this multipath distortion. In the figure, 71 is FIG.
The composite wave M (t) is the input signal x0 shown in FIG. Reference numeral 72 denotes the demodulated signal y1 shown in FIG. 10, which is the right side of the equation (8). The horizontal axis t is time, and the vertical axis is each signal x0,
The size of y1. As can be seen from this figure, the multipath distortion appears as a sharp pulse-like waveform in the demodulated signal y1.

FIG. 12 shows the case where t = 0 to 1/10000 when w _d = -20000π (frequency difference: 10 kHz) and r = 0.9.
It is the result of calculating dφ / dt during the period (w _d t = 0 to 2π). The condition under which a particularly large distortion occurs at this time is when w _d t is approximately π (radian).
This is a case where the direct wave and the reflected wave cancel each other, and the amplitude of the combined wave is minimized.

As described above, the received FM wave is a direct wave
Even if it is an FM demodulator that can perform FM demodulation without any problem when it is a (direct wave), the direct wave and the reflected wave (reflected wave)
In a multipath situation in which a composite wave of the signal (wave) is received, there is a problem that a large distortion occurs in the demodulated signal. The present invention has been made in view of such circumstances, and an object of the present invention is to provide an FM demodulator that can suppress distortion of a demodulated signal under a multipath condition.

[0024]

An FM demodulator according to the present invention includes an FM demodulator for switching between a first FM demodulation operation and a second FM demodulation operation to perform FM demodulation of a received signal. The FM demodulation operation and the second FM demodulation operation have different responses to a change in the amplitude of the received signal in the demodulated signal output from the FM demodulation means.

Further, the FM demodulator according to the present invention includes switching control means for controlling switching between the first demodulation operation and the second demodulation operation based on the amplitude of the received signal.

Further, in the FM demodulator according to the present invention, the switching control means switches the demodulation operation of the FM demodulation means when the amplitude of the received signal becomes smaller than a predetermined value.

Further, in the FM demodulator according to the present invention, a demodulating means for outputting a signal whose amplitude changes according to the frequency and amplitude of the received signal; an amplitude detecting means for detecting the amplitude of the received signal; A correction coefficient calculating means for outputting a correction coefficient based on the amplitude detected by the amplitude detecting means; a switching means for switching and outputting a correction coefficient output from the correction coefficient calculating means and a predetermined correction coefficient; Amplitude correction means for correcting the amplitude of the output signal of the demodulation means based on the output correction coefficient and outputting the corrected signal as a demodulated signal.

Further, in the FM demodulator according to the present invention, a demodulating means for outputting a signal whose amplitude changes according to the frequency and amplitude of the received signal; an amplitude detecting means for detecting the amplitude of the received signal; Switching means for switching and outputting the amplitude detected by the amplitude detecting means and a predetermined value, correction coefficient calculating means for outputting a correction coefficient based on the output of the switching means, and correction coefficient output by the correction coefficient calculating means Amplitude correction means for correcting the amplitude of the output signal of the demodulation means based on the above, and outputting the corrected signal as a demodulated signal.

Further, the FM demodulator according to the present invention includes switching control means for controlling switching in the switching means based on the amplitude of the received signal.

In the FM demodulator according to the present invention, when the amplitude of the received signal is smaller than a predetermined value, the switching control means reduces the amplitude correction amount in the amplitude correction means. To control the switching.

In the FM demodulator according to the present invention, the demodulator outputs a signal whose amplitude changes in accordance with the frequency and amplitude of the received signal, the amplitude detector detects the amplitude of the received signal, Correction coefficient calculation means for performing a polynomial approximation calculation based on the amplitude detected by the amplitude detection means and outputting the calculation result as a correction coefficient; and correcting the amplitude of the output signal of the demodulation means based on the correction coefficient output by the correction coefficient calculation means. And an amplitude correcting means for outputting the corrected signal as a demodulated signal.

Further, in the receiver according to the present invention,
The receiver includes a receiving unit that receives a combined wave of a direct wave and an indirect wave from a transmitter, and the FM demodulator to which the received combined wave is input as a received signal.

Further, in the receiver according to the present invention, the receiving means includes an AGC amplifier for amplifying the composite wave, and a signal amplified by the AGC amplifier is input to the FM demodulator as the reception signal. Is done.

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Conventional FM demodulator shown in FIG. 11, the response characteristics between the input signal x ₀ · Output signal y ₁ (so-called transfer function) was always constant. For example,
As shown in Expressions (5) and (6), the response characteristic is always a pure time derivative of the phase component p or φ of the input signal x0.
y1 = was _{C 1 · dp / dt = C} 1 · dφ / dt.

The FM demodulator of the first embodiment includes a plurality of response characteristics are different for the amplitude change of the input signal x ₀ F
The M demodulation operation is switched and performed. For example, when the received signal is a direct wave, performs FM demodulation operation having the response characteristics of _{y1 = C 1 · dp / dt} , when the received signal is a composite wave, y1 = A _² C ² FM with response characteristics of (dφ / dt)
Perform demodulation operation. In particular, in the first embodiment, a plurality of FM demodulation operations having different responses to the amplitude of the received signal are performed by switching.

In the first embodiment, whether the received signal is a direct wave or a composite wave is determined based on the magnitude of the amplitude of the received signal. The FM demodulation operation is switched. here,
If the amplitude of the received signal is smaller than a predetermined value, it is determined that the received signal is a composite wave. If the amplitude of the received signal is larger than a predetermined value, it is determined that the received signal is a direct wave. I do.

Here, for convenience, the phase component of the input signal x0 when the received signal is a direct wave is denoted by p, and the phase component of the input signal x0 when the received signal is a composite wave is denoted by φ. Also, C ₁ and C ₂ are each an arbitrary constant, A is the amplitude of the input signal x0.

Hereinafter, a case where the first demodulation operation for performing the same amplitude correction (correction for removing the amplitude change response component) as in the related art and the second demodulation operation for which the amplitude correction is not performed is switched and performed will be described as an example. The FM demodulator according to the first embodiment will be described.

FIG. 1 is a configuration diagram illustrating the FM demodulator according to the first embodiment. In the drawings, the same or corresponding parts as those in the related art are denoted by the same reference numerals, and description thereof is omitted. In the figure, 2
Reference numeral 4 denotes a first demodulation operation switching unit, and a coefficient output unit 241
, A coefficient switching unit 242, and a coefficient switching control unit 243. The first demodulation operation switching unit 24 outputs the coefficient “1” to the correction coefficient calculation unit 22 when the output of the amplitude detection unit 21 is smaller than the predetermined value A _min , and otherwise outputs the amplitude detection The input from the section 21 is output to the correction coefficient calculating section 22. The operation of the FM demodulator when the output of the amplitude detector 21 is directly input to the correction coefficient calculator 22 is the same as the conventional one.

This will be described in detail. The amplitude detection unit 21 detects the amplitude of the input signal x0, and outputs the detection result to the coefficient switching unit 242 as a coefficient z0. The coefficient output unit 241 outputs the coefficient “1”.
Is output to the coefficient switching unit 242 as a coefficient z2. The coefficient switching unit 242 performs a first operation of outputting the coefficient z0 of the inputted coefficients z0 and z2, and a coefficient z2 of the inputted coefficients z0 and z2.
Is performed by switching between the second operation and the second operation of outputting the output. The correction coefficient calculation unit 22 calculates a correction coefficient that is inversely proportional to the output coefficient of the coefficient switching unit 242, and outputs the calculation result to the amplitude correction unit 23 as a correction coefficient z1. The amplitude correction unit 23 calculates the correction coefficient z1
Is multiplied by the output signal y0 of the demodulation unit 20, and the result of the multiplication is output as a demodulated signal y1.

The output z0 of the amplitude detector 21 is also input to the coefficient switching controller 243. Coefficient switching control unit 243
Is the coefficient z0 is smaller than the predetermined value A _min is allowed output coefficients z2 from the coefficient switching unit 242 performs control allowed to output the coefficient z0 from the coefficient switching section 242 in other cases. Specifically, the coefficient switching control unit 243, if the coefficient z0 is smaller than the predetermined value A _min, it is determined that the input signal x0 is a composite wave, in order to allowed to stop the amplitude correction in the amplitude correction unit 23, the amplitude The coefficient z1 is set to “1” so that the amplitude correction section 23 does not perform the amplitude correction practically. On the other hand, if the coefficient z0 is greater than the predetermined value A _min, as the coefficient switching control unit 243 determines that the input signal x0 is a direct wave, similar to the conventional amplitude correction is performed in the amplitude correction unit 23, the coefficient The switching unit 242 outputs the coefficient z0.

When the input signal x0 is a composite wave,
The signals x0, y0, y1 are exemplified as follows by using mathematical expressions. First, the input signal x0 is represented by the formula (6) the composite wave M (t) shown in, x0 = M (t) = sin (w c t) + r · sin {(w c + w d) t} = {1 + 2 r · cos (w _d t) + r ² } ^1/2 sin (w _c t + φ) (9) Here, it is _{φ = arctan [sin (w d} t) / {1 + r · cos (w d t)}] ··· (10).

The output signal y0 of the demodulation unit 20 is given by the following equation (4).
Since A ² T (dφ / dt) / 2, y0 ≒ [{1 + 2 r · cos (w _d t) + r ² } ^1/2 ] ² · T · [-r · w _d {r + cos (w _d t)} / {1 + 2 r cos (w _d t) + r ² }] / 2 =-rw _d {r + cos (w _d t)} · T / 2 ··· (11 ). However, dφ / dt corresponds to dp / dt in equation (4),
The amplitude A of the composite wave M (t) is {1 + 2 r · cos (w _d t) + r ² } ^1/2
It is. Here, the right side of the equation (11), Yosu to note that contains the amplitude A ² as shown in Equation (4) by offsetting numerator and denominator.

The amplitude detector 21 detects the input signal x0 as in the prior art.
, That is, the square of the amplitude of the composite wave M (t). The first demodulation operation switching unit 24 detects that the output of the amplitude detection unit 21 is small by comparing with the predetermined value A _min ,
The coefficient “1” is output to the correction coefficient calculator 22. The correction coefficient calculation unit 22 outputs the reciprocal of the coefficient “1”, that is, “1” to the amplitude correction unit 23. The amplitude corrector 23 multiplies the coefficient y1 from the correction coefficient calculator 22 by the output y0 of the demodulator 20, and outputs the result as a demodulated signal y1. That is, the amplitude correction unit 23 does not perform the amplitude correction.

Therefore, the output signal y0 of the demodulator 20 shown in the equation (11) is the output signal (demodulated signal) y1 of the amplitude corrector 23.
Y1 ≒ −rw _d {r + cos (w _d t)} · T / 2 (12)

FIG. 2 is a diagram illustrating the demodulated signal y1 shown in equation (12). In the figure, reference numeral 91 denotes the demodulated signal y1,
That is, the input signal x0 to the demodulation unit 20 is a composite wave,
This is a demodulated signal y1 when the amplitude correction by the amplitude correction unit 23 is not performed. 71 is a conventional demodulated signal y1,
That is, the input signal x0 to the demodulation unit 20 is a composite wave,
This is a demodulated signal y1 when amplitude correction is performed by the amplitude correction unit 23. Reference numeral 92 denotes a conventional amplitude correction unit 23.
Is the correction coefficient z1 input to the. In the demodulated signal 91 not subjected to the amplitude correction as described above, sharp pulse-shaped distortion is suppressed as compared with the conventional demodulated signal 92 subjected to the amplitude correction, and the multipath distortion is suppressed.

As described above, F in Embodiment 1
The M demodulator switches between a plurality of FM demodulation operations having different response characteristics, particularly different response characteristics with respect to an amplitude change of an input signal, so that multipath distortion can be suppressed.

For example, multipath distortion can be suppressed by not performing the amplitude correction conventionally performed when performing FM demodulation of the synthesized wave.

Further, according to the magnitude of the amplitude of the received signal,
Determine whether the received signal is a direct wave or a composite wave,
Since the plurality of FM demodulation operations are switched based on the determination result, multipath distortion can be accurately suppressed.

Embodiment 2 In the first embodiment, when the input signal x0 to the demodulation unit 20 is a composite wave, the multipath distortion can be suppressed by stopping the amplitude correction by the amplitude correction unit 23 illustrated in FIG. That was explained. However, if the multipath distortion is small,
Even if the input signal x0 is a composite wave, it may be better to perform amplitude correction. For example, if the amplitude of the demodulated signal is
If the distortion caused by responding to the amplitude change of x0 (that is, the distortion due to the amplitude change response component) is larger than the multipath distortion, the amplitude correction is performed even under the multipath situation. As a result, a demodulated signal with less distortion can be obtained as a result.

In order to stop the amplitude correction operation only in a state where the multipath distortion is particularly large, the predetermined value A _min to be compared in the coefficient switching control section 243 shown in FIG. Alternatively, a threshold may be provided for the correction coefficient z1 input to the coefficient switching control unit 243, and when the correction coefficient z1 exceeds the threshold, the amplitude correction operation in the amplitude correction unit 23 may be stopped. This clearly shows that the suspension period of the amplitude correction operation can be limited to a period in which the multipath distortion is particularly large, because the “amplitude correction coefficient” increases as the multipath distortion increases, as shown in FIG.

As described above, by setting the value of the predetermined value A _min to be compared in the coefficient switching control section 243 to an appropriate value, the amplitude correction operation can be stopped only in a state where the multipath distortion is large.

Embodiment 3 In the first and second embodiments, the multipath distortion is suppressed by stopping the conventionally performed amplitude correction under a predetermined condition. In the third embodiment, instead of the process of stopping the amplitude correction operation, the amount of amplitude correction in the amplitude correction unit 23 is reduced as compared with the conventional case, thereby suppressing multipath distortion.

FIG. 3 is a diagram illustrating a demodulated signal y1 different from FIG. In the figure, 93 is the demodulated signal y1 shown in FIG. 1, and 94 is the correction coefficient z1 shown in FIG. In FIG. 2, when the input signal x0 is a composite wave, the amplitude correction is stopped in almost all periods. On the other hand, in FIG. 3, the amplitude correction is not stopped, but only the correction amount is reduced. Here, the correction amount is reduced only in a state where the multipath distortion is large.

Specifically, the correction coefficient z1 shown in FIG.
Is exceeded, the correction coefficient is limited to 10 to obtain a demodulated signal y1 as shown in FIG. At this time, the coefficient output unit 241 shown in FIG. 1 outputs A _min = 0.1.
As described above, if the amplitude correction amount in the amplitude correction unit 23 is extremely large, the amplitude correction amount can be reduced.
The distortion of the demodulated signal y1 can be effectively suppressed.

As described above, the multipath distortion can be effectively suppressed by reducing the amount of correction compared to the amplitude correction conventionally performed when FM demodulating the composite wave.

Embodiment 4 FIG. FIG. 4 shows F of the fourth embodiment.
FIG. 2 is a configuration diagram illustrating an M demodulator; In the drawings, the same or corresponding parts as those in the related art are denoted by the same reference numerals, and description thereof is omitted.
Here, a second demodulation operation switching unit 25 is provided in place of the first demodulation operation switching unit shown in FIG. When the input from the correction coefficient calculating unit 22 is larger than the predetermined value _Kmax, the second demodulation operation switching unit 25 sends the coefficient “
1 "is output, otherwise, the input from the correction coefficient calculation unit 22 is output to the amplitude correction unit 23. FM when the output of the correction coefficient calculation unit 22 is output to the amplitude correction unit 23 as it is. The operation of the demodulator is the same as in the prior art.

The operation will be described. The demodulation unit 20 calculates the value of y0 ≒ A ² C ₂ (dφ
/ dt). Further, the amplitude detection unit 21 outputs the input signal x
Outputs the square of the amplitude A of 0 (A ² ). Correction coefficient calculator 22
Calculates a correction coefficient inversely proportional to the square of the amplitude of the FM modulation signal, that is, C ₃ / A ² , and outputs the result to the second demodulation operation switching unit 25 as in the related art. When the input from the correction coefficient calculation unit 22 is smaller than a predetermined value _Kmax, the second demodulation operation switching unit 25 outputs the value to the amplitude correction unit 23 as it is. The amplitude corrector 23 multiplies the output of the amplitude corrector 23 by the output of the demodulator 20 and outputs the result as a demodulated signal y1.

Next, when the input from the correction coefficient calculating unit 22 is larger than the predetermined value _Kmax , the second demodulation operation switching unit 25 sets the predetermined value _Kmax instead of the input value.
Is output to the amplitude correction unit 23. With the above operation, the magnitude of the correction coefficient can be limited, and multipath distortion can be suppressed.

Embodiment 5 FIG. FIG. 5 shows the FM shown in FIG.
FIG. 3 is a configuration diagram illustrating an FM demodulator having a configuration different from that of the demodulator 30; In the figure, 30 is an FM demodulator, 20
Denotes a demodulator, 21 denotes an amplitude detector, 22 denotes a correction coefficient calculator,
23 is an amplitude correction unit, and 24 is a first demodulation operation switching unit. 201 and 202 are multipliers, 203 is a local oscillator, 204 is a phase shifter, 205 is a low-pass filter, 206
Is a low-pass filter, 207 and 208 are delay units, 209
And 210 are multipliers, 211 is a subtractor, and 212 is a low-pass filter.

The operation of the demodulation unit 20 will be described below. First, the input FM signal x0 is x0 = A cos {w _c kT + p (kT)}, and the output from the local oscillator 203 is cos (w _c · kT),
The output of the phase shifter 204 obtained by shifting this by 90 ° is sin (w _c k
T), the output x6 of the multiplier 202 and the multiplier 2
The output x7 of 03 is x6 = A cos {p (kT)} / 2 x7 = A sin {p (kT)} / 2. Thus, the outputs x8 and 208 of the delay unit 207
X9 = A cos {p ((k-1) T)} x9 = A sin {p ((k-1) T)}.

As described above, the outputs x10 and 2 of the multiplier 209
Each 10 output x11 of, x10 = x6 · x9 = A 2 [sin {p (kT) + p ((k - 1) T)} + sin {p (kT) - p ((k - 1) T) }] / 4 x11 = x7 · x8 = A ² [sin {p (kT) + p ((k-1) T)}-sin {p (kT)-p ((k-1) T)}] / It becomes 4. The output x12 of the result of the subtractor 211 is x12 = x
10-x11 = A ² sin {p (kT)-p ((k-1) T)} / 2. This is similar to the quadrature detection output shown in equation (4).

[0063] Further, by employing the amplitude detector 21 shown in FIG. 1 as an amplitude detector 21, the output x13 of the amplitude detector ^{21, x13 = x6 2 + x7 2} = A 2/2 , and the process immediately input The amplitude of the signal x0 can be obtained.

As described above, even in the FM demodulator having the configuration shown in FIG. 5, the conventional demodulator 2 shown in FIG.
Since the first and second demodulation operation switching sections 24 shown in FIG. 5 perform the same operations as the first demodulation operation switching section 24 shown in FIG. By doing so, multipath distortion can be suppressed.

Embodiment 6 FIG. FIG. 6 shows F of the sixth embodiment.
FIG. 2 is a configuration diagram illustrating an M demodulator; In the figure, the same or corresponding parts as those in FIG.
Here, the operation of the correction coefficient calculating means 36 is different from the other embodiments.

The function required by the correction coefficient calculator 22 shown in FIG. 1 is to find the reciprocal 1 / x of the input value x. On the other hand, the correction coefficient calculating means 36 in the sixth embodiment calculates the reciprocal 1 / x based on the polynomial approximation calculation.
A value corresponding to is calculated. For example, 1 / x is calculated as 3.073
By calculating by approximating 11-3.11606 x + 1.04275 x ² , the input value x is changed from 0.8 to 1.2 as shown in FIG.
Calculate the value of 1 / x with high accuracy within the range.
In the figure, 93 is a value calculated by the correction coefficient calculating means 36 based on a polynomial approximation calculation, and 94 is a true value of 1 / x. Thus, the value of the input data x is 0.8
If it is out of the range of 1.2, an error will occur.
When the value of the input data x decreases, a value smaller than the true value is calculated.

Therefore, in a situation where the correction coefficient has conventionally been large, the correction coefficient output from the correction coefficient calculation means 36 approaches the constant term of the polynomial approximation, and the correction coefficient can be limited. That is, the amplitude correction amount can be controlled without using a special determination unit such as the coefficient switching control unit 243 shown in FIG. 1, and multipath distortion can be suppressed with a simple configuration. Here, the polynomial approximation calculation includes, for example, a constant term, a term proportional to the first power of an input value,
It is a polynomial with a term proportional to the square of the input value.

Embodiment 7 As shown in FIG. 10, in a conventional receiver, a limiter intermediate frequency amplifier 6 is provided in a stage preceding an FM demodulator. This limiter intermediate frequency amplifier 6
Is to level out fluctuations in the received signal level due to changes in the distance between the receiver and the transmitter. In the seventh embodiment, instead of the limiter intermediate frequency amplifier 6, automatic gain control (Automatic Gain control) is performed.
Control: hereinafter referred to as AGC).

The conventionally used limiter intermediate frequency amplifier 6 outputs a constant saturation voltage when the level of the input signal exceeds a predetermined value. On the other hand, the AGC intermediate frequency amplifier is an amplifier whose gain is automatically controlled so that the level of the output signal is kept substantially constant. In particular, the AGC intermediate frequency amplifier employed in the seventh embodiment performs amplification so that amplitude fluctuation due to multipath included in the input signal remains by performing the gain control relatively slowly. As a result, the switching of the amplitude correction shown in the first embodiment is quickly performed, and the effect of suppressing multipath distortion is increased.

FIG. 8 is a configuration diagram illustrating a receiver according to the seventh embodiment. In the figure, the same or corresponding parts as those in the related art and FIG. In the figure, reference numeral 15 denotes an AGC intermediate frequency amplifier.

As described above, when the AGC intermediate frequency amplifier is used in the preceding stage of the FM demodulator, the signal input to the FM demodulator rarely becomes a saturation voltage as in the case where the limiter intermediate frequency amplifier is used. First demodulation operation switching unit 24
Appropriate switching in can be expected. Also, this AGC
By causing the intermediate frequency amplifier to perform the gain control relatively slowly, the first demodulation operation switching unit 2 shown in FIG.
4, a signal containing a multipath amplitude fluctuation can be input.

[0072]

Since the present invention is configured as described above, it has the following effects. The FM demodulator according to the present invention includes FM demodulation means for switching between the first FM demodulation operation and the second FM demodulation operation to perform FM demodulation of a received signal, and performs the first FM demodulation operation and the second FM demodulation operation. In the FM demodulation operation, the response to the amplitude change of the received signal in the demodulated signal output from the FM demodulation means differs, so that FM demodulation with less multipath distortion can be performed.

Further, the FM demodulator according to the present invention includes the switching control means for controlling the switching between the first demodulation operation and the second demodulation operation based on the amplitude of the received signal. The effect of suppressing multipath distortion is great.

Further, in the FM demodulator according to the present invention, a demodulating means for outputting a signal whose amplitude changes according to the frequency and amplitude of the received signal; an amplitude detecting means for detecting the amplitude of the received signal; A correction coefficient calculating means for outputting a correction coefficient based on the amplitude detected by the amplitude detecting means; a switching means for switching and outputting a correction coefficient output from the correction coefficient calculating means and a predetermined correction coefficient; Amplitude correction means for correcting the amplitude of the output signal of the demodulation means based on the output correction coefficient, and outputting the corrected signal as a demodulated signal. Can be obtained at

In the FM demodulator according to the present invention, the demodulator outputs a signal whose amplitude changes in accordance with the frequency and amplitude of the received signal; the amplitude detector detects the amplitude of the received signal; Switching means for switching and outputting the amplitude detected by the amplitude detecting means and a predetermined value, correction coefficient calculating means for outputting a correction coefficient based on the output of the switching means, and correction coefficient output by the correction coefficient calculating means And an amplitude correcting means for correcting the amplitude of the output signal of the demodulating means based on the above, and outputting the corrected signal as a demodulated signal, so that an FM demodulator with less multipath distortion can be obtained with a simple configuration. it can.

Further, in the FM demodulator and the receiver according to the present invention, a demodulating means for outputting a signal whose amplitude changes according to the frequency and amplitude of the received signal, and an amplitude detecting means for detecting the amplitude of the received signal A correction coefficient calculating means for performing a polynomial approximation calculation based on the amplitude detected by the amplitude detecting means and outputting a calculation result as a correction coefficient; and a correction signal output from the demodulating means based on the correction coefficient output by the correction coefficient calculating means. Since an amplitude correcting means for correcting the amplitude and outputting the corrected signal as a demodulated signal is provided, it is possible to obtain an FM demodulator with less multipath distortion with a simple configuration.

Also, in the receiver according to the present invention,
A receiving means for receiving a combined wave of a direct wave and an indirect wave from a transmitter, and an AGC amplifier for amplifying the combined wave,
Since the signal amplified by the AGC amplifier is input to the FM demodulator as the reception signal, the reception signal can be input to the FM demodulator without attenuating the amplitude fluctuation due to multipath as much as possible. A receiver with less multipath distortion can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an FM demodulator according to a first embodiment;

FIG. 2 is a diagram illustrating a demodulated signal according to the first embodiment;

FIG. 3 is a diagram illustrating a demodulated signal according to a third embodiment;

FIG. 4 is a configuration diagram illustrating an FM demodulator according to a fourth embodiment;

FIG. 5 is a configuration diagram illustrating an FM demodulator according to a fifth embodiment;

FIG. 6 is a configuration diagram illustrating an FM demodulator according to a sixth embodiment;

FIG. 7 is a diagram illustrating an example of reciprocal operation by a correction coefficient operation unit;

FIG. 8 is a configuration diagram illustrating a receiver according to a seventh embodiment;

FIG. 9 is a schematic diagram illustrating a conventional FM demodulator.

FIG. 10 is a configuration diagram illustrating a receiver having a conventional FM demodulator;

FIG. 11 is a configuration diagram illustrating details of the conventional FM demodulator shown in FIGS. 9 and 10;

FIG. 12 is a diagram illustrating a conventional multipath distortion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Antenna 2 Amplifier 3 Frequency converter
Reference Signs List 4 local oscillator 5 intermediate frequency filter 6 limiter intermediate frequency amplifier 7 pre-filter 8 AD converter 9 FM demodulator 10 DA converter 11 audio amplifier 12 speaker 20
Demodulation unit 21 Amplitude detection unit 22 Correction coefficient calculation unit 23 Amplitude correction unit 24 First demodulation operation switching unit 25 Second demodulation operation switching unit 30 FM demodulator 36 Correction coefficient calculation unit 241 coefficient output unit
242 coefficient switching unit 243 coefficient switching control unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Masayuki Tsuji 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. (72) Masahiro Tsujishita 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Corporation F-term (reference) 5K020 CC03 DD01 DD09 EE05 HH11

Claims (10)

[Claims] An FM demodulation means for switching between a first FM demodulation operation and a second FM demodulation operation to perform FM demodulation of a received signal, wherein the first FM demodulation operation and the second FM demodulation operation comprise:
An FM demodulator characterized in that the demodulated signal output from the FM demodulating means has a different response to a change in amplitude of the received signal. 2. The apparatus according to claim 1, further comprising a switching control unit that controls switching between the first demodulation operation and the second demodulation operation based on an amplitude of the received signal. FM demodulator. 3. The F-mode switching device according to claim 2, wherein the switching control unit switches the demodulation operation of the FM demodulation unit when the amplitude of the received signal is smaller than a predetermined value.
M demodulator. 4. A demodulator for outputting a signal whose amplitude changes according to the frequency and amplitude of a received signal; an amplitude detector for detecting the amplitude of the received signal; and a correction based on the amplitude detected by the amplitude detector. Correction coefficient calculating means for outputting a coefficient, switching means for switching and outputting a correction coefficient output by the correction coefficient calculating means and a predetermined correction coefficient, and demodulation means based on the correction coefficient output by the switching means. An FM demodulator comprising: an amplitude corrector that corrects the amplitude of an output signal and outputs the corrected signal as a demodulated signal. 5. A demodulator for outputting a signal whose amplitude changes according to the frequency and amplitude of a received signal; an amplitude detector for detecting the amplitude of the received signal; an amplitude detected by the amplitude detector; Switching means for switching and outputting the value of the correction coefficient; a correction coefficient calculating means for outputting a correction coefficient based on the output of the switching means; and an amplitude of an output signal of the demodulating means based on the correction coefficient output by the correction coefficient calculating means. And an amplitude correcting means for outputting the corrected signal as a demodulated signal. 6. The FM demodulator according to claim 4, further comprising switching control means for controlling switching in said switching means based on the amplitude of said received signal. 7. The switching control means controls switching such that when the amplitude of the received signal decreases below a predetermined value, the amplitude correction amount in the amplitude correction means is reduced. The FM demodulator according to claim 6. 8. A demodulator for outputting a signal whose amplitude changes according to the frequency and amplitude of the received signal; an amplitude detector for detecting the amplitude of the received signal; and a polynomial based on the amplitude detected by the amplitude detector. Correction coefficient calculating means for performing an approximate calculation and outputting the calculation result as a correction coefficient; and correcting the amplitude of the output signal of the demodulation means based on the correction coefficient output by the correction coefficient calculating means, and converting the corrected signal to a demodulated signal. An FM demodulator comprising: an amplitude correction unit that outputs the result as a signal. 9. An FM demodulator according to claim 1, wherein said receiving means receives a combined wave of a direct wave and an indirect wave from a transmitter, and said received combined wave is inputted as a received signal. And a receiver. 10. The reception means includes an AGC amplifier for amplifying the composite wave, and a signal amplified by the AGC amplifier is input to the FM demodulator as the reception signal. Receiver.