JPS61265928A - Am receiver - Google Patents

Abstract

PURPOSE:To attain disturbing wave rejection due to a signal of an adjacent station and the reproduction with excellent fidelity with simple constitution by applying AM detection by a synchronous detector and using an orthogonal component detecting signal to control the frequency characteristic of a high cut-off filter. CONSTITUTION:A collector current of a transistor (TR) Q3 is decreased when an output V0 of a synchronous detector 6 gets higher and an output V1 of an electric field strength detection circuit 12 gets lower. A control voltage Vc is decreased when the output V0 of the synchronous detector 6 gets higher and the output V1 of the electric field strength detection circuit 12 gets lower. Thus, a level of a disturbing wave separated from a reception desired station signal is higher in the audio frequency band, the ratio of input/output at a frequency region higher than the cut-off frequency of the high-cut circuit 10 is decreased, that is the attenuation is increased to reject the disturbing wave. When the level of the disturbing wave is lower and the electric field strength gets higher, the control voltage Vc rises and the attenuation of the high band of the high-cut circuit 10 is decreased to attain reproduction with high fidelity.

Description

[Detailed description of the invention] 9th reciprocal The present invention relates to an AM receiver.

BACKGROUND ART AM receivers, unlike FM receivers, are designed to capture and reproduce even radio waves with a considerably weak electric field. Therefore, when a weak electric field radio wave is received, it is desirable to suppress the noise component and increase the S/N ratio of the reproduced sound, even if it sacrifices the fidelity of reproduction to some extent. For this reason, conventional A
Normally, a noise suppression circuit consisting of a so-called high-cut circuit is used in the low-frequency amplification stage of the M receiver to cut high-frequency components of the reproduced audio signal, thereby suppressing noise components. The high-cut circuit is configured such that the high-frequency attenuation characteristic changes depending on a signal corresponding to the received electric field strength, such as an AGC (automatic gain control) voltage of an AM receiver.

However, in such conventional AM receivers, when the bandwidth of the IF (intermediate frequency) stage is widened to improve fidelity, it is not possible to remove interference waves such as beat noise that occur when adjacent station signals are present. However, there is a problem in that it is necessary to separately provide a detection circuit for detecting adjacent station signals and to control the bandwidth of the IF stage using this detection circuit, resulting in a complicated configuration.

SUMMARY OF THE INVENTION An object of the present invention is to provide an AM receiver that can eliminate interference waves caused by adjacent station signals with a simple configuration and has excellent fidelity.

The AM receiver according to the present invention performs AM detection using an in-phase component detection means that generates an in-phase component detection signal corresponding to the level of a component in phase with a carrier component in a received signal, and which is orthogonal to the carrier component in the received signal. The apparatus is configured to include orthogonal component detection means according to the level of the component, and to change the amount of attenuation of the high frequency component in the high frequency cut filter for noise suppression according to the orthogonal component detection signal.

Friend-1-3 Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In FIG. 1, an RF (high frequency) received signal from an antenna 1 is amplified by an RF amplifier 2, and then mixed with a local oscillation signal by a mixer 3 and subjected to IF times signal conversion. I
The F-fold signal is amplified by the IF amplifier 4 and then supplied to the in-phase detector 5 as in-phase component detection means, the in-phase detector 6 as quadrature component detection means, and the limiter amplifier 7. In the limiter amplifier 7, the amplitude of the IF multiplied signal is limited, resulting in a signal containing only the carrier wave component. This limiter amplifier 7
The carrier wave component outputted from the carrier wave component is supplied to a phase detector 8, and the phase difference with the output of a VCO (1! pressure controlled oscillator) 9 is detected. The output of this phase detector 8 is supplied to the control input terminal of the VCO 9, and a signal (90°
) and a signal (0°) in phase with the carrier component are output from the VCO 9.

The signal (90") output from this VCO 9 is supplied to the phase detector 8 and at the same time serves as a detection reference signal for the in-phase detector 6. Therefore, the carrier wave component in the IF signal from the synchronous detector 6 The signal (Oo) output from the VCO 9 serves as a detection reference signal for the synchronous detector 5, and
Meanwhile, a component in phase with the carrier component in the IF signal is detected and output as an AM detection output. The outputs of these synchronous detectors 5 and 6 are supplied to a high cut circuit 10 and a control voltage generation circuit 11, respectively. The output of the electric field strength detection circuit 12 is supplied to the control I voltage generation circuit 11 . The electric field strength detection circuit 12 is configured to generate a signal at a level corresponding to the electric field strength by smoothing the IF multiplied signal output from the circuit at the stage before the final stage of the multistage amplifier circuit forming the IF amplifier 4. The control voltage generation circuit 11 changes depending on the output of the quadrature synchronous detector 6 and the output of the field strength detection circuit 12, and generates a low level signal when the level of the quadrature component becomes large or when the field strength becomes weak. It is configured to output a controlled 1W pressure VC. The control voltage Vc output from the control voltage generation circuit 11 is supplied to the high cut circuit 10. The high cut circuit 10 is
The control voltage VC is configured to change the attenuation characteristic in the high range of the audio signal band. The high-cut circuit 10 outputs the AM detection output with high-frequency components cut off to the audio output terminal OUT.

In the above configuration, it is assumed that there is a desired reception station signal consisting of an AM wave corresponding to a vector A based on the phase of a carrier wave as shown in FIG.

At the same time, the frequency is ∆ from this desired reception station signal.
If there is an adjacent station signal that is higher by ω and corresponds to vector B, the composite signal er of this adjacent station signal and the desired reception station signal will correspond to vector C. This composite signal e is expressed as the following equation, assuming that the frequency of the carrier wave is ω0.

er=Acosω□t+Bcos(ω0+Δω)t
-.--.-(1) If the equation (1) is expressed in a form in which it is decomposed into the in-phase component and the orthogonal component of the carrier wave, the following equation is obtained.

e r= (A+BcosΔωt) −cosωot−
BSinΔωt −Sin (Zoo t −・−・−
(2) IF multiplied signal synchronous detector 5 such as this composite signal er
and 6, an in-phase component (2) and a quadrature component Q as shown in the following equations are obtained.

1=A+BcosΔωt・・・・・・(3)Q −−B
sin Δωt−・−・−(4) Therefore, in the synchronous detection output from the synchronous detector 5, the desired reception station signal a and the interference wave due to the adjacent station signal are separated from each other within the audio frequency band, as shown in FIG. It will be done. Further, the synchronous detector 6 outputs a signal corresponding to the level of the interference wave.

Incidentally, the AM detection output modulus when envelope detection is performed is expressed as follows.

d=J (A+BcosΔωt)2+(BsinΔωt
)! =JA ” +8” +2ABcosΔωt...
(5) From equation (5), it can be seen that when envelope detection is performed, the desired reception station signal a and the interfering signal cannot be separated.

Therefore, by changing the high-frequency attenuation characteristics of the high-cut circuit 10 depending on the level of the output of the synchronous detector 6, the interference waves can be removed.

Here, the level of the output Vo of the synchronous detector 6 increases as the level of the interference wave increases, as shown in FIG.
And the level of the output (1) of the electric field strength detection circuit 12 is
As shown in the figure, the electric field strength increases as it becomes stronger. Further, the frequency characteristic of the high cut circuit 10 is the sixth
It shall be as shown in the figure. That is, in FIG. 6, the characteristic indicated by the solid line e is the characteristic when the control voltage VC is the lowest, and as the frequency increases beyond the cutoff frequency, the input/output ratio decreases at a predetermined slope. Furthermore, as the control voltage VC increases, the input/output ratio decreases with a slope smaller than the predetermined slope as the frequency increases beyond the cutoff frequency.

At this time, the III mm pressure generating circuit 11 is formed as shown in FIG. In FIG. 7, the output Vo of the synchronous detector 6 and the output 1 of the field strength detection circuit 12 are applied to the bases of transistors Q2 and Q3. The emitters of these transistors Q2 and Q3 are the transistor Q
They are commonly connected together with one emitter. A constant current source Io is connected between the common emitter connection point of these transistors Q+*Qz+Q3 and ground. A reference voltage y rer is applied to the base of the transistor Q1. The collectors of transistors Q+ and Q2 are connected to the power supply Vc.
c is supplied. The collector current of transistor Q3 is transmitted through current mirror circuit 1 consisting of transistors Q4 and Qs.
There are 5 inputs. A resistor R is connected between the collector of the transistor Q5 serving as the output end of the current mirror circuit 15 and ground. The voltage drawn across this resistor R is the control l voltage VC.

In this configuration, the collector current of the transistor Q3 changes according to the difference in voltage applied to the bases of the transistors Q1 to Q3, and when the output Vo of the synchronous detector 6 becomes high and the output of the field strength detection circuit 12 ■Decreases when 1 becomes low.

Since a current equal in phase to the collector current of the transistor Q3 flows through the resistor R by the action of the current mirror circuit 15, the control voltage Vc increases when the output o of the synchronous detector 6 becomes high and the output o from the field strength detection circuit 12 increases. It decreases when 1 becomes low.

Therefore, when the level of the interfering wave separated from the desired station signal within the audio frequency band becomes high, 60
As the voltage VC decreases, the high cut circuit 10
The input/output ratio in the high frequency range above the cutoff frequency is small, that is, the amount of attenuation is large, and the interference waves are removed.

Furthermore, when the level of the interference wave is low and the electric field strength is high, the control voltage VC increases, and the attenuation amount of the high frequency range of the high-cut circuit 10 becomes small, so that high-fidelity reproduction is performed. Become.

Incidentally, in the above embodiment, the IF double signal limiter amplifier 7
Although the signal is supplied to the phase detector 8 via the IF multiplier signal limiter amplifier 7, it is also possible to supply the signal directly to the phase detector 8 without passing through the IF multiplier signal limiter amplifier 7. It is also conceivable to replace the phase detector 8 in the above embodiment with the synchronous detector 6.

Effects of the Invention As detailed above, the AM receiver according to the present invention performs AM detection using an in-phase detector and increases the AM detection output using a quadrature component detection signal corresponding to the level of a component orthogonal to a carrier component in a received signal. Since it is configured to control the frequency characteristics of the high-frequency cut filter that cuts high-frequency components,
With a simple configuration that does not include a circuit for controlling the bandwidth of the IF stage, interference waves caused by adjacent station signals can be separated and removed from the desired reception station signal, and when the level of interference waves is small, the electric field When the intensity increases, the amount of attenuation of the high-frequency components in the high-frequency cut filter is reduced, and reproduction with excellent fidelity can be achieved.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a vector diagram showing the phases of the desired signal and interference wave signal, and Fig. 3 is a synchronization of the composite signal of the desired signal and interference wave. FIG. 4 is a graph showing the characteristics of the synchronous detector 6; FIG. 5 is a graph showing the characteristics of the field strength detection circuit 12; FIG. is a graph showing the characteristics of the high-cut circuit 10, and FIG. 7 is a circuit diagram showing a specific circuit example of the control voltage generating circuit 11. Explanation of symbols of main parts 5.6... Synchronous detector 10... High cut circuit 11... Control voltage generation circuit 12... Field strength detection circuit

Claims (1)

[Claims] An AM receiver that suppresses noise by using a high-frequency cut filter that attenuates high-frequency components in the audio signal band of the AM detection output while changing attenuation characteristics according to the received electric field strength, and is in phase with the carrier wave component in the received signal. AM detection is performed by an in-phase component detection means that generates a frequency component detection signal corresponding to the level of the carrier wave component in the received signal, and an orthogonal component detection signal that generates a quadrature component detection signal corresponding to the level of the component orthogonal to the carrier wave component in the received signal. What is claimed is: 1. An AM receiver comprising a component detection means, the attenuation amount of the high frequency component in the high frequency cut filter being changed in accordance with the orthogonal component detection signal.