JPS58223926A - Synchronous detecting receiver - Google Patents

Abstract

PURPOSE:To exerise smooth automatic gain control without being affected by the presence or absence of a modulation signal, by extracting a signal proportional to the amplitude of a carrier signal for exercising automatic gain control. CONSTITUTION:An output of a synchronous detector 7 is applied to a low pass filter 10 for DC component extraction. The filter 10 can extract a low frequency component from a DC to 50-100Hz, extracts the DC component proportional to the amplitude of the carrier signal, and the automatic gain control is exercisid by feeding back the DC component to a high frequency amplifier 1, an intermediate frequency amplifier 4 or a mixer 3. As a result, the control is exercised in response to the carrier signal amplitude without being affected by the modulation signal.

Description

[Detailed Description of the Invention] The present invention relates to a synchronous detection receiver, and in particular improves its automatic gain control method. Smooth gain control is intended to prevent distortion that occurs when the amplification gain becomes too large when modulation starts again from the state, resulting in the signal becoming too large in the receiver. This is what I did.

In recent years, with the widespread use of wireless communications, the frequency range in use has been expanding towards higher frequencies, but this trend has led to the need to use the currently used bands more effectively, or in other words, to increase the frequency band occupied. There is a noticeable tendency to adopt communication methods with as small a width as possible. In particular, in shortwave broadcast bands, etc., interference tends to increase, so there is a tendency to introduce a single sideband communication system with a reduced carrier wave in place of the conventional double sideband communication system.

In that case, apart from special business use, it is desired that the general receiver is not so complicated and expensive as compared to the conventional double-sideband type receiver.

Reduced-carrier single-sideband amplitude modulation has traditionally been implemented using fairly large-scale equipment, mainly in fixed-line communications for commercial use, but such equipment has been used for home use such as general broadcast reception. Introducing it in its original form would be quite difficult from a cost standpoint.

Therefore, it is possible to reduce the cost of the receiver by using a PLL that can be easily integrated into an IC, but in that case, there is a problem in performing automatic gain control as described later. Unless this problem is solved, it will be extremely difficult to apply the reduced carrier single sideband amplitude modulation method to broadcasting, etc., and to spread the use of receivers widely and put it into practical use.

SUMMARY OF THE INVENTION In view of the above-mentioned points, an object of the present invention is to appropriately solve the problems in performing the above-mentioned automatic gain control when a reduced carrier single sideband amplitude modulation method is put into practical use. An object of the present invention is to provide a synchronous detection receiver.

In order to achieve such an object, the present invention includes a receiving means for receiving an input amplitude modulated wave, and a receiver for regenerating a carrier wave component from the received input amplitude modulated wave.
l k -7' Means 2.1 A synchronous detection means for synchronously detecting the received input amplitude modulated wave based on the generated gh'''' carrier 2 wave component and extracting a synchronous detection output signal, and the synchronous detection output signal. It is characterized by comprising means for extracting a low frequency component mainly including a direct current component from the receiver, and returning the low frequency component containing mainly a direct current component to the receiving means to automatically control the profit of the receiving means. do.

The present invention will be described in detail below with reference to the drawings.

First, we will outline the configuration of a conventionally used reduced carrier single sideband amplitude modulated wave receiver and discuss the problems associated with its automatic gain control.

FIG. 1 shows an example of the configuration of such a conventional synchronous detection receiver, in which carrier-reduced single sideband amplitude modulated radio waves are transmitted to the antenna (
After receiving the signal at a high frequency amplifier (not shown), it is supplied to a high frequency amplifier l for amplification, and its amplified output is supplied to a mixer J together with a local oscillation output from a local oscillator. The mixed output of the mixer 3 is supplied to an intermediate frequency amplifier to obtain an intermediate frequency signal. The intermediate frequency signal obtained by the receiving means with the above configuration is filtered through a narrowband crystal filter! A carrier wave necessary for demodulation is extracted by supplying the carrier wave signal to a limiter amplifier 6.

The signal is amplified to a constant amplitude as a carrier wave for synchronous detection, and is supplied to a synchronous detector together with the above-mentioned intermediate frequency signal to demodulate the original signal.

At the same time, the carrier signal extracted from the narrowband crystal filter 3 is also supplied to the rectifier 1, and the resulting rectified voltage is fed back to the high frequency amplifier 1 and intermediate frequency amplifier DA or mixer 3 to perform their automatic gain control. conduct. This takes advantage of the fact that the obtained rectified voltage is proportional to the magnitude of the carrier wave signal, but in this method using a narrowband crystal filter, the oscillation frequency of the local oscillator is Since it must be highly stable and the narrowband crystal filter is also expensive, it has conventionally been used in a limited number of synchronous detection receivers for commercial use such as fixed communications.

However, in order for the general public to receive broadcast signals, it is necessary to use a low-cost receiver, rather than an expensive receiver that uses a narrowband crystal filter j as described above. For that purpose, as shown in Figure 2, a narrowband crystal filter is needed! Instead, it has been considered to use a 7-factor loop circuit (PLL) q to regenerate the carrier signal and supply it to the synchronous detector 7. PLL 9 is cheaper than a narrowband crystal filter, and PLL 9 is cheaper than a narrowband crystal filter. Since the self-oscillation frequency of changes to follow the carrier signal in the intermediate frequency signal while being locked, the local oscillation frequency does not need to be highly stable in the case of the receiver of FIG. 1, so it can be constructed at low cost. For this reason, the PLL system is becoming widely used in coherent detection receivers for broadcasting.

However, when using a PLL, although the PLL locks to the phase of the carrier signal frequency in the intermediate frequency signal, it has its own amplitude that is unrelated to the amplitude of the carrier signal. It was not possible to obtain a rectified voltage proportional to the amplitude of the carrier signal required for this purpose. Therefore, for automatic gain control in this case, as shown in Figure 2, the entire intermediate frequency signal including the carrier signal and modulation signal is supplied to rectifier l, and the rectified voltage is fed back for automatic gain control. It was thought to do.

With this method, a problem occurs the moment modulation is applied again after a non-modulated state has continued for a while. In other words, since no modulation continues, the rectified voltage for automatic gain control is a small value until modulation is applied again, and therefore the amount of feedback to the high frequency amplifier/intermediate frequency amplifier or mixer 3 is small. , the gain of these receiving means/, 4/ or 3 is in a high state. When the high frequency input signal has a waveform as shown in FIG. 3(A), for example, when modulation starts again at time a, the rectified voltage for automatic gain control changes at time a as shown in FIG. 3(B). It rises after that.

However, receiving means 1. It takes time for the rectified voltage to rise before the gain of 3 or 3 is reduced, and the gain is still high during the time between point a and point a.
Therefore, an excessive signal is generated in the receiver, and a large distortion occurs in the detected output, such as clipping of the detected output as shown in FIG. 3(C).

In addition, since automatic gain control is performed based on the combined amplitude of the signal obtained by combining the carrier signal and the modulation signal, the PLL
The carrier wave amplitude in the input signal to the receiver always fluctuates under the influence of the modulation signal. Therefore, if the signal input to the receiver is low or if only the modulated signal component increases relatively due to selective fading, the carrier signal component in the input signal to the PLL 9 will decrease. This can also cause the PLL to become unlocked.

Furthermore, in this method, the greater the reduction in the carrier wave of the single sideband amplitude variation W1''1 radio wave, the greater the amount of the above-mentioned distortion, which becomes an obstacle to sufficiently reducing the carrier wave.

Therefore, for the above reasons, in order to realize appropriate automatic gain control in a coherent detection receiver using PLI, it is necessary to apply the reduced carrier single sideband amplitude variable method to general broadcasting and to spread it widely. This was essential, and its realization was eagerly awaited.

In view of the above points, in the present invention, even in an IN period detection receiver using a PLL, if a signal proportional to the amplitude of the carrier signal is extracted and automatic gain control is performed, it is not affected by the presence or absence of a modulation signal. , we focus on the fact that automatic gain control can be performed.

Figure 3 shows an example of the basic configuration of the receiver of the present invention, where:
The same parts as in FIG. 1 or 2 will be designated by the same reference numerals. In the present invention, the synchronous detection output of the synchronous detector 7 is supplied to the low-pass filter /θ for extracting the DC component.

This low-pass filter 10 is mainly used to extract a DC component, and is capable of extracting, for example, a low frequency component of about 5θ to 100 Hz from the DC component. This low-pass filter IO extracts a DC component proportional to the amplitude of the carrier signal in the following manner, and uses this DC component to transmit the signal to the high frequency amplifier l and intermediate frequency amplifier l or mixer 3 as the receiving means described above. Returns and performs automatic gain control.

Note that the output of the synchronous detector 7 is supplied to the audio amplifier /I to reproduce the original signal as usual. Incidentally, in the audio amplifier 1/, it is customary that the signal in the audio frequency band output from the synchronous detector is amplified.

Now, the intermediate frequency signal e at the output of the intermediate frequency amplifier l
(t) is expressed as the following equation (1) in the unit cost waveband amplitude modulation of carrier reduction using the upper sideband.

e(t) −EcCO3a+c t + E+rllJ
]S(Ole +c++m)t (1
) Here, Ec - the amplitude of the carrier signal ωC - the angular frequency of the carrier signal Em - the amplitude of the modulation signal ωm - the angular frequency of the modulation signal PLL From 9, a signal ep(t) locked to the frequency and phase of the carrier signal is obtained. 0 this signal appears as output e
(t), where the amplitude is E, e (t) −Epcosa+e t
G2). Output 8o of synchronous detector 7 (
Since t) is the product of e(t) and e (t), eo(t) - e(t) x ep(t) - evil h+no. ,Ko. at +2 2 In this equation (3), the first term is the DC component, and E is the PLL
Since the amplitude value is a constant value of 9, a component proportional to the amplitude Ee of the carrier signal is obtained. Therefore, by extracting this DC component, the influence of the modulation signal amplitude can be removed.

In the present invention, such a DC component is extracted by the low-pass filter 10, thereby obtaining a voltage proportional to the amplitude of the carrier signal, which is fed back to receiving means such as a high frequency amplifier l or an intermediate frequency amplifier l. As a result, automatic gain control corresponding only to the carrier wave signal amplitude is performed regardless of modulation, whether during non-modulation or modulation, and the above-mentioned conventional disadvantages are resolved.

FIG. 3 shows a multiphase system applied to a coherent detection receiver that receives audio broadcasting using single sideband amplitude modulation with carrier reduction. The intermediate frequency signal from the intermediate frequency amplifier is transferred to the second synchronous detector/3.
This synchronous detector 13 is also supplied with a 90 degree phase shifter/2.
Coherent detection is performed based on a carrier wave signal whose phase is shifted by 90 degrees from . The detection outputs of both synchronous detectors 7 and 13 are further supplied from the voice frequency 90 degree phase shifter iy to the matrix circuit B to produce sum and difference signals, and from this matrix circuit 15, the upper sideband and the modulated signal are The lower sideband can be taken out, and either one of them can be selected and output using the switch lB.

In the broadcasting synchronous detection receiver of this example as well, the direct current component is mainly extracted from the synchronous detector 7 by the low-pass filter /θ, and automatic gain control can be performed only on the carrier signal.

Although the extracted automatic gain control voltage is fed back to the high frequency amplifier l and the intermediate frequency amplifier da in FIGS. 1 and 3, it is of course possible to feed it back to the mixer 3 as well. Alternatively, such DC component may be fed back only to a specific amplifier. Furthermore, the level adjustment amplifier is
It may be added where necessary.

Note that it is also possible to receive double-sided band amplitude modulated waves using the configuration shown in Figure 4, and it is also possible to receive only one sideband of the double-sided band amplitude modulated waves using the example shown in Figure 3. be. That is, according to the present invention, it is possible to provide a synchronous detection receiver that is compatible with both the double sideband amplitude modulation method and the single sideband modulation method.

As is clear from the above, according to the present invention, when receiving a single-sideband amplitude modulated radio wave with a reduced carrier wave, automatic gain control of a synchronous detection receiver using a PLL applied to the carrier wave signal can be applied to the modulation. This can be done in response to the carrier signal amplitude without being affected by the signal. Therefore, the signal does not become excessive at the moment when modulation is restarted after a non-modulated state continues, and distortion caused by such an excessive signal can be eliminated. Further, according to the present invention, it is possible to prevent the PLiL from losing lock when the signal input level to the receiver is low or when the modulated signal component increases relatively due to selective aging. From the above points,
According to the present invention, the carrier wave of the transmitted radio wave can be significantly reduced, and therefore there are advantages in terms of transmission and frequency utilization, such as saving transmission power and reducing interference caused to others.

Additionally, the present invention is compatible with both double-sideband and single-sideband amplitude modulation schemes.

Furthermore, although the present invention has been explained above with reference to the case where signals in the voice band are mainly handled, the present invention is effective when applied not only to signals in the voice band but also to any desired frequency band. Of course.

[Brief explanation of drawings]

Figures 1 and 2 are block diagrams showing two examples of conventional synchronous detection receivers, and Figures 3 (4) to (C) show that distortion occurs in the detection output due to automatic gain control. FIG. 4 is a block diagram showing a basic configuration example of the present invention, and FIG. 3 is a block diagram showing another embodiment of the present invention. /...High frequency amplifier, Co...Local oscillator, 3.
...mixer, da...intermediate frequency amplifier, j
...Narrowband crystal filter, t...Limiter amplifier, 7...Synchronous detector, l...
... Rectifier, 9...PLL/θ...Low-pass filter that extracts low-frequency components mainly including DC components, //
...Audio amplifier, 12...Carrier wave 90 degree phase shifter, /3...Synchronized detector, /41...Audio frequency 90 degree phase shifter, 15...Matrix circuit, /6... ·switch.

Claims (1)

[Claims] a receiving means for receiving an input amplitude modulated wave; a phase-locked loop means for regenerating a carrier wave component from the received input amplitude modulated wave; and synchronous detection and synchronization of the received input amplitude modulated wave based on the reproduced carrier wave component. a synchronous detection flat stage for extracting a detection output signal; a synchronous detection stage for extracting a low-frequency component mainly including a DC component from the synchronous detection output signal; and feeding back the low-frequency component mainly containing a DC component to the receiving means; 1. A synchronous detection receiver comprising means for automatically controlling gain.