JPS6233765B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention proposes a signal receiving method that demodulates a received signal by restoring a pure carrier wave without using a phase-locked loop with a low loop gain, in a signal receiving method compatible with a reduced carrier single sideband signal transmission method. The purpose of the present invention is to solve various problems that occur when using the above-mentioned phase-locked loop and to ensure stable signal reception. For convenience of explanation, some analysis will be made regarding the characteristics of the reduced carrier wave single sideband signal. The modulated signal V ₀ (t) when a sine wave signal having an angular frequency ω _S is amplitude-modulated with a modulation degree m using a carrier wave having an angular frequency ω _C is given by the following equation. V ₀ (t)=(1+msinω _S t) cosω _C t ......(1) Based on equation (1), the reduced carrier single sideband signal V ₁
(t) can be expressed by the following equation using the upper single sideband. V ₁ (t) = kcosω _C t + m/2 sin (ω _C + ω _S ) t ... ... (2) However, k < 1 Regrouping equation (2) assuming that the carrier wave is subjected to amplitude modulation and phase modulation. The following formula is obtained. however In other words, if we simply envelope detect this reduced carrier single sideband signal, we get

A signal proportional to [Equation] is obtained, which has a waveform different from the original modulated wave, and if phase detection is performed, a signal proportional to (t) expressed by Equation (4) is obtained. Next, a conventional reduced carrier single sideband signal reception method and its problems will be described. FIG. 1 shows a conventional example, and its operation will be explained below. The received signal of the reduced carrier single sideband represented by equation (2) is guided to the mixer 2 together with the local oscillation signal obtained from the local oscillator 3 via the antenna 1. The output signal of the mixer 2 passes through an intermediate frequency band pass filter 4, is amplified in level by an intermediate frequency amplifier 5, and is applied to an amplitude limiting amplifier 6 and a product detection circuit 10. In the signal whose amplitude is limited to a constant value by the amplitude limiting amplifier 6, the amplitude term in V ₁ (t) shown in equation (3) is replaced with a constant value, and the carrier angular frequency is ω.
The intermediate angular frequency ω _IF is used instead of _C , and the amount of phase modulation becomes a phase-modulated signal as shown by (t) in equation (4). The output signal obtained from the amplitude limiting amplifier 6 is applied to a phase locked loop 12 comprising a phase comparator 7, a low pass filter 8 and a voltage controlled oscillator 9. The characteristics of this phase-locked loop 12 include the sensitivity of the phase comparator 7, the frequency characteristics of the low-pass filter,
Although it is determined by the sensitivity of the voltage controlled oscillator, the design technique for this loop is well known, so a detailed description of its operation will be omitted. If the characteristics of the phase-locked loop are appropriately designed, the output signal of the phase-locked loop 12, that is, the output signal obtained from the voltage-controlled oscillator 9, becomes a signal V ₂ ( t) and is expressed by the following equation. V ₂ (t)=Asin(ω _IF t+α) ……(5) However, A and α are constants. In order for the output signal of the phase-locked loop 12 to be given by equation (5), the design guidelines for this loop are to keep the loop gain well below 1 in the range of angular frequencies where the angular frequency ω _S of the modulation signal exists. Needless to say, it is important to do so. The output signal of the phase-locked loop described above together with the output signal obtained from the intermediate frequency amplifier 5 described above is
It is added to a product detection circuit 10 composed of a double-balanced differential amplifier or the like. The output signal obtained from the intermediate frequency amplifier 5 is (2)
It can be expressed using the intermediate angular frequency ω _IF instead of ω _C shown in the equation or equation (3), and this can be expressed as V ₁ '(t) as shown in the following equation. V ₁ ′(t)=B[kcosω _IF t+m/2sin(ω _IF +ω _S )t...(6) However, B is a constant determined by the reception level, the mixer, the gain of the intermediate frequency amplifier, etc. The product detection circuit 10 is Basically, it multiplies two input signals, so (5), (6)
By multiplying the expression, its output can be obtained. The output of the product detection circuit 10 is a low-pass filter 1 that passes only the angular frequency component of the modulation signal.
1 to the output terminal 13. Therefore, the signal obtained at the output terminal 13 is
Among the signal components obtained after performing the multiplication of equations (5) and (6), only signals having the modulation signal angular frequency and angular frequencies in the vicinity thereof are obtained, and by performing calculations, it can be given by the following equation. I understand. V ₀ (t)=Cmsin(ω _S t+θ) …………(7) θ=tan ^-1 cos α/sin α …………(8) However, C is a constant. In other words, the signal obtained from the output terminal 13 is
The result is a demodulated signal with a phase delay of θ as shown by equation (8). However, the conventional example shown in FIG. 1 has the following problems. That is, in order to obtain the output signal shown in equation (5) from which the phase modulation component is removed from the phase-locked loop 12, the loop gain must be made sufficiently small in the frequency range where the modulation signal exists, as described above. . Now considering a signal having an audio frequency band as a modulating signal, the above gain condition lengthens the pull-in time for the phase-locked loop to reach its normal state and generally narrows the range of phase lock. This has the disadvantage that when tuning the receiver, a beat sound is generated for a long time before and after the tuning point, and the drift of the local signal frequency causes the phase-locked loop to become out of synchronization. It was hot. The present invention eliminates these drawbacks and
Phase-detects the phase modulation component included in the received signal,
Using this detection output, a carrier wave from which the phase modulation component has been removed is restored by applying new phase modulation to the signal from which the amplitude modulation component has been removed from the received signal so as to cancel out the phase modulation component,
The present invention is characterized in that the modulated signal is demodulated by performing product detection on the received signal using this carrier wave. An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows an embodiment of the present invention.
Blocks or terminals having the same functions as those in the figures are given the same numbers, and further explanation will be omitted. In FIG. 2, the output signal of the amplitude-limiting amplifier 6 is composed of a frequency demodulator 14, which can be realized using various known circuit techniques, and a monostable multivibrator, for example, or a variable delay line, which is used as a phase modulator. is added to the time axis modulator 16. It goes without saying that the frequency demodulator 14 may be accompanied by a generally used low-pass filter for carrier removal. Frequency demodulator 1
The output of 4 is applied to an integrating circuit 15. The frequency demodulator 14 and the integrating circuit 15 together serve as a phase detector. The output signal obtained from this integrating circuit 15 is applied to the time axis modulator 16 together with the output signal obtained from the amplitude limiting amplifier 6 described above. This time axis modulator 16 applies the output signal of the amplitude limiting amplifier 6 to the integration circuit 15.
A time delay is added by an amount proportional to the output signal obtained from the output signal. This time axis modulator 16
The output signal has only a carrier wave component and is applied to the product detection circuit 10, which performs the same operation as in FIG. 1. Next, a process by which the output signal of the time axis modulator 16 can be made into a signal having only a carrier wave component will be explained. Output signal V ₃ obtained from amplitude limiting amplifier 6
(t) is when the amplitude of the signal shown in equation (3) is kept constant,
It is expressed by the following equation where the carrier wave angular frequency ω _C becomes the intermediate angular frequency ω _IF . V ₃ (t)=Dsin(ω _IF t+(t))...(9) However, D is a constant and (t) is shown by equation (4). On the other hand, the output signal V ₄ obtained from the integrating circuit 15
(t) is the frequency demodulator 14 and the integration circuit 15
Since it plays the role of a phase detector, it is expressed by the following equation. V ₄ (t)=l(t) (10) However, l is a constant and is the sensitivity of the phase detector. Therefore, if the delay time added by the time axis modulator 16 is τ, the output signal V ₅ (t) of the time axis modulator 16 is expressed by the following equation. V ₅ (t)=Dsin{ω _IF t−ω _IF τ+(t −τ)} …(11) By the way, the above delay time τ is as mentioned above.
Since it is designed to be proportional to V ₄ (t), it is expressed by the following equation. τ=q+pv ₄ (t)=q+pl(t) (12) However, p is a constant and becomes the sensitivity of the time axis modulator. q is a constant. By substituting equation (12) into equation (11), the following equation is obtained. V ₅ (t) Dsin {ω _IF t-ω _IF pl(t) + (t-τ)-ω _IF q} ......(13) Equation (13) is an amplitude-limited amplifier by the time axis modulator 16. This shows that the phase modulation component of the output signal of No. 6 can be canceled out, and it can be seen that if the constants p and l are selected so that the following equation holds true, it can be completely canceled out. ω _IF pl(t)=(t−τ)……(14) Next, consider the range in which equation (14) can be established. Now, suppose that pl is selected so that ω _IF pl=1 …………(15), and the intermediate frequency is
Considering the case of 455KHz, in this case, from equation (15), pl is: pl=1/ω _IF =1/2a×455×10 ³ [se
c/rad]. On the other hand, the range of possible values for (t) is
Considering that (t) is expressed by equation (4), it can be seen that the range is from -π/2 radians to π/2 radians. Therefore, it can be seen that the variable range of the delay time τ in this case is pl×π [sec], that is, about 1 microsecond. On the other hand, (t) is changed by the signal angular frequency ω _S as shown in equation (4), but if we consider a signal in the audio frequency domain, a time delay of about 1 microsecond will cause the signal to hardly change. Don't change it. That is, in this case, (t) and (t-τ) shown in equation (14) can be considered to be practically equal. Therefore, in the case of a reduced carrier wave single sideband signal targeting a signal in the audio frequency domain, if equation (15) is satisfied, the objective can almost be achieved. That is, in this case, the output signal of the time axis modulator 16 becomes a signal having only a carrier wave component, and the product detection circuit 10 obtains a demodulated signal similar to that shown in FIG. By the way, in the present invention shown in FIG. 2, the carrier wave component is extracted without using a phase-locked loop with a low loop gain as in the case of FIG.
Problems such as beat sounds that occur before and after the tuning point during tuning operations do not occur, and there are no problems with the pull-in range of the phase-locked loop. FIG. 3 shows still another embodiment of the present invention, and like FIG. 2, blocks or terminals having the same functions as those in FIGS. Explanation will be omitted. In FIG. 3, a phase-locked loop ₁₂ having the same configuration as in FIG. It differs from FIG. 1 in that it is designed to be larger and is used as a frequency demodulator. Also, the difference between FIG. 2 and this FIG.
This case is superior in that a stable output with good S/N can be applied to the time axis modulator 16 over a wide range of received signal levels. Note that in a frequency region where the loop gain of the phase-locked loop 12 is greater than 100, the phase modulation components of the output signal of the amplitude-limiting amplifier 6 and the output signal of the voltage-controlled oscillator 9 are approximately equal, so other operations are performed as follows. It is the same as Figure 2. By the way, in FIG. 3, since a phase-locked loop with a sufficiently large loop gain is used, the pull-in time is sufficiently short, and the occurrence of unpleasant beat sounds before and after the tuning point during tuning operation can be practically eliminated. The retraction range can also be made sufficiently wide. As detailed above, according to the present invention, it is possible to stably receive a reduced carrier single sideband signal,
The generation of unpleasant beat sounds before and after the tuning point during tuning operation can be eliminated, and the effect is great. In addition, in the above explanation, in order to simplify the explanation, a single superheterodyne method without adding a high frequency amplifier was explained as an example, but the present invention can be implemented without being influenced in any way by the configuration of the receiver front end section. It goes without saying that there is.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a reception method for a reduced carrier single sideband signal, FIG. 2 is a block diagram showing one embodiment of the present invention, and FIG. 3 is a block diagram showing another embodiment of the present invention. be. 1...Antenna, 2...Mixer, 3...Local oscillator, 4...Intermediate frequency band pass filter, 5
...Intermediate frequency amplifier, 6...Amplitude limiting amplifier, 7
...Phase comparator, 8...Low pass filter, 9...
...Voltage controlled oscillator, 10...Product detector,
11...Low pass filter, 12...7, 8, 9
A phase-locked loop consisting of 13... demodulated signal output terminal, 14... frequency demodulator, 15...
Integrating circuit, 16...time axis modulator.

Claims (1)

[Claims] 1. A signal obtained by adding a single sideband signal of a modulated carrier wave amplitude-modulated by a first signal and a reduced carrier wave in which the level of a carrier wave component included in the modulated carrier wave is reduced, In the so-called reduced carrier single sideband signal transmission method for transmitting the first signal,
A signal reception method adapted to a receiver that uses the above-mentioned added signal as a reception signal, the method comprising: a means for phase-detecting a phase modulation component included in the reception signal, comprising a frequency demodulator and an integrating circuit; Using the detection output from the detection means to remove the amplitude modulation component from the received signal, new phase modulation is applied to the signal so as to cancel out the phase modulation component, thereby restoring the carrier wave from which the phase modulation component has been removed. 1. A signal receiving system characterized in that the first signal is demodulated by product detection of the received signal using a carrier wave from the modulating means. 2. The signal receiving system according to claim 1, characterized in that a phase-locked loop with a loop gain sufficiently larger than 1 is used as the frequency demodulator.