JPH08139621A - Radio receiver - Google Patents

Abstract

PURPOSE: To effectively suppress an interference wave without attenuating a desired wave signal more than needed even in the state of the existence of the strong interference wave by limiting the signal amplification factor of an amplifier for RF detection small when the desired wave signal is extremely small. CONSTITUTION: The amplification factor of an amplifier 11 for RF detection is varied corresponding to the output level of an IF detector 12 for detecting an intermediate frequency (IF) signal level so that the amplification factor of the amplifier 11 for RF detection can be enlarged when the output of the IF detector 12 is large but can be reduced when the output of the IF detector 12 is small. Therefore, when receiving the weak desired wave signal on the condition of the strong interference wave, the loop gain of AGC including the amplifier 11 for RF detection is lowered, the attenuation degree of an input signal due to an attenuator 2 is reduced, and the level of the desired wave signal is kept almost at the original level. On the other hand, the interference wave is suppressed as much as possible by the selection characteristics of an RF tuner 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in radio receivers, and more particularly to an AM radio receiver in which sensitivity suppression of a desired signal is reduced without aggravating interference due to interfering waves.

[0002]

2. Description of the Related Art FIG. 5 shows the structure of a conventional AM radio receiver.

In the figure, 1 is an antenna, 2 is an attenuator, 3 is an RF amplifier, 4 is an RF tuner, 5 is a local oscillator, 6 is a mixer, and 7 is a band pass filter (hereinafter referred to as BPF).
8) AM demodulator, 9 RF detector, 10 M
IX input AGC amplifier, 13 is an RF detection amplifier.

The operation of the AM radio receiver configured as above will be described below.

In FIG. 5, the signal received by the antenna 1 passes through the attenuator 2 and is input to the RF amplifier 3, where RF
It is amplified by the amplifier 3. The output signal of the RF amplifier 3 is input to the RF detection amplifier 13 and the RF tuner 4.

The RF tuner 4 has a selection characteristic of selecting a desired wave signal, is tuned to a desired wave signal frequency desired by a viewer, selects a desired wave signal from the inputted signals, and mixes it with the mixer 6. To enter. After that, the desired wave signal is mixed with the local oscillation output of the local oscillator 5 by the mixer 6 to be converted into an intermediate frequency signal, and is input to the AM demodulator 8 via the BPF 7 which passes the intermediate frequency frequency band. And
The AM demodulator 8 demodulates the intermediate frequency signal and outputs the demodulated output as an audio signal.

The MIX input AGC amplifier 10 has an R
The output of the F tuner 4 is amplified, and the amplified signal and R
The signal amplified by the F detection amplifier 13 is RF
It is input to the detector 9.

The RF detector 9 level-detects the output of the RF detection amplifier 13 or the output of the MIX input AGC amplifier 10, and the higher one of the detection levels is set by the RF detector 9. If the level exceeds the set level, the attenuator 2 is used until the detection level drops below the set level.
Increase the attenuation of. As a result, the output of the mixer 6 and R
The output of the F amplifier 3 is kept below a certain value.

The attenuator 2 has two capacitors C21 and C22.
And a pin diode D21, the input signal from the antenna 1 is connected to the impedance of the capacitor C21 and the capacitor C21.
22 and the series circuit of the pin diode D21,
The antenna input signal is divided and attenuated, and the divided output is input to the RF amplifier 3. The junction capacitance of the pin diode D21 is changed by the current output from the RF detector 9,
The attenuation amount of the attenuator 2 is controlled by changing the voltage division ratio of the series impedance.

The RF detection amplifier 13 has an input capacitance C1.
And three resistors R1, R2, and R3, two NPN transistors Q1 and Q2, a bias voltage source Vr1, and a current source Io13, and the amplification degree is a fixed value. Is.

The RF detector 9 is a level detector 9a composed of two rectifying diodes D91 and D92, a peak hold capacitor C91, and a time constant setting resistor R91.
And a current source Io9, two PNP transistors Q91,
Q92 and a differential current source 9b including a level setting reference voltage source Vr9.

FIG. 6 is a spectrum of each part in the conventional AM radio receiver shown in FIG. 5 when a relatively strong desired wave signal and a strong disturbing wave that can be sufficiently received from the antenna 1 are simultaneously input. Is shown in FIG.
6A is an input of the antenna 1, D is a desired wave, U is an interfering wave, FIG. 6B is an output spectrum of the RF amplifier 3, and FIG. 6C is a frequency characteristic of the RF tuner 4. Figure 6
(D) shows the input spectrum of the mixer 6.

The desired wave signal and the interfering wave input as shown in FIG. 6 (a) are both shown in FIG. 6 (b) by the wide band AGC loop constituted by the RF detection amplifier 13, the RF detector 9 and the attenuator 2. 6B, the output spectrum of the RF amplifier 3 is as shown in FIG. 6B because it is attenuated by the attenuator 2 so as not to exceed a certain level X shown in FIG. Since the RF tuner 4 has the bandpass characteristic shown in FIG. 6C centering on the desired wave signal frequency, the output spectrum of the RF tuner 4 becomes as shown in FIG. 6D. In this way, the level of the interfering wave U is controlled by the action of the broadband AGC loop,
The interference wave level input to the mixer 6 is limited to a certain level or less. As a result, the interference of the interference wave modulation signal with the desired wave due to the nonlinearity of the mixer 6 can be prevented.

[0014]

However, in the conventional AM radio receiver shown in FIG. 5, when the desired wave signal input from the antenna 1 is weak, and when the interference wave input at the same time is strong, It has the following drawbacks:

That is, FIG. 7 shows a spectrum of each part when a weak desired wave signal and a strong interfering wave are simultaneously input from the antenna 1 in the conventional AM radio receiver, and FIG. It is an input of the antenna 1, D is a desired wave, U is an interfering wave, and FIG.
7 (c) shows the frequency characteristic of the RF tuner 4, and FIG. 7 (d) shows the input spectrum of the mixer 6. As in the case of FIG. 6, the interference wave U is a wide band AG.
Since the level is limited by the operation of the C loop, the input spectrum of the mixer 6 becomes as shown in FIG. 7 (d). That is, it shows that the originally weak signal D of the desired wave is not sufficiently amplified due to the level limitation of the interfering wave U. FIG. 8 shows the output of the AM demodulator 8 in the state of FIG. 7, and shows that the noise component generated in the RF amplifier 3 and the like is larger than the interference component due to the interfering wave U. In other words, wideband AGC to prevent interference
Due to the action of the loop, the sensitivity of the receiver to the desired wave signal has dropped too much.

As described above, in the conventional AM radio receiver, when a strong interfering wave is input while receiving a weak desired wave signal, the AGC operation based on the detection level of the interfering wave signal component functions. Then, the level of the desired wave signal was limited more than necessary, and the desired wave could hardly be received.

The present invention solves the above-mentioned conventional drawbacks, and an object of the present invention is to prevent the interference of the interference group as in the conventional case when a strong desired wave signal is received in the presence of a strong interference wave. In addition to effectively preventing it, when receiving a weak desired wave signal in the presence of a strong disturbing wave, without disturbing the desired wave signal more than necessary, the disturbing wave can be confirmed within the range where the reception of the desired wave signal can be confirmed. It is to provide a radio receiver that can be effectively suppressed.

[0018]

In order to achieve the above object, in the present invention, as described above, the RF tuner has a desired wave selection characteristic having a band pass characteristic centered on the desired signal frequency. Paying attention to the level limitation of the interfering wave, when the desired wave signal is extremely small, the signal amplification factor of the RF detection amplifier is limited to a small amount, and the reduction amount of the attenuation amount of the attenuator by the RF detector is reduced. By so doing, the level of the interfering wave is effectively limited by the selection characteristic of the RF tuner while the desired wave signal is kept at the original value.

That is, in the radio receiver of the present invention as defined in claim 1, an attenuator for varying the amount of attenuation of the antenna input signal by a control voltage, an RF amplifier for amplifying the output of the attenuator, and an output of the RF amplifier. An RF tuner for extracting a desired wave signal from the mixer, a mixer for converting an output of the RF tuner into an intermediate frequency signal by mixing with a local oscillation output, and a band pass filter for extracting an intermediate frequency signal component from the output of the mixer And an IF detector that detects the output level of the band pass filter and an output signal of the RF amplifier, and the degree of amplification of the IF detector that includes the demodulator that demodulates the intermediate frequency signal that has passed through the band pass filter. Is the above I
An RF detection amplifier that is controlled according to the output of the F detector and an output level of the RF detection amplifier, and the detection output is applied to the attenuator as the control voltage.
The detector is provided with a detector.

According to a second aspect of the invention, in the radio receiver according to the first aspect of the invention, the amplification degree of the RF detection amplifier is large when the output of the IF detector is large, and the output of the IF detector is large. When is small, it is controlled to be small.

Furthermore, the invention of claim 3 is the radio receiver of the invention of claim 1 or claim 2, wherein the output of the RF tuner is separately amplified and the amplified signal is converted to R.
An AGC amplifier for outputting to the F detector is provided, and the RF detector is provided with an output level of the RF detection amplifier and the AGC.
The configuration is characterized in that the higher one of the output levels of the operational amplifier is detected and the detected output is given to the attenuator as a control voltage.

[0022]

With the above construction, in the radio receivers according to the first and second aspects of the invention, when the output of the IF detector for detecting the intermediate frequency signal level is high, the amplification degree of the RF detection amplifier is increased. Then, when the output of the IF detector is small, the amplification degree of the RF detection amplifier is changed according to the output level of the IF detector so that the amplification degree of the RF detection amplifier is reduced.

Therefore, when a weak desired wave signal is received in a situation where the interference wave is strong, an AG including an RF detection amplifier is used.
The loop gain of C is reduced, the amount of attenuation of the input signal by the attenuator is reduced, and the level of the desired wave signal is maintained almost unchanged. On the other hand, the interference wave is suppressed as much as possible by the selection characteristic of the RF tuner. Therefore, even if the S / N ratio is poor, the desired wave signal can be received without disappearing.

Further, when the interference wave is strong and the desired wave signal is relatively large, the level I of the intermediate frequency signal is detected.
The output voltage of the F detector increases, and the gain of the RF detection amplifier increases. Therefore, the desired wave signal is attenuated together with the interfering wave, but the desired wave signal is large and does not disappear.
Moreover, the interfering wave is suppressed to a small level by the selection characteristic of the RF tuner. Therefore, when receiving a relatively strong desired wave signal, interference of a strong interfering wave can be prevented as in the conventional case, and a relatively strong desired wave signal can be received with a high S / N ratio.

According to the third aspect of the invention, when the desired wave signal is larger than the interfering wave, the output level of the AGC amplifier becomes higher than the output level of the RF detection amplifier, and the RF detector is , The output level of the AGC amplifier is detected, and the attenuation amount of the attenuator is controlled, so that both the desired wave signal and the interfering wave are attenuated as in the conventional case.
The interference wave is suppressed to a small extent by the selection characteristic of the RF tuner, and the desired wave signal is received with a high S / N ratio.

[0026]

EXAMPLES An example of the present invention will be described below.

FIG. 1 shows an embodiment of an AM radio receiver according to the present invention, in which 1 is an antenna, 2 is an attenuator, and 3 is R.
F amplifier, 4 RF tuner, 5 local oscillator, 6 mixer, 7 BPF, 8 AM demodulator, 9 RF detector, 1
Reference numeral 0 is an amplifier for MIX input AGC, which has the same configuration as the conventional example. Reference numeral 12 is an IF detector that detects the output level of the BPF 7, and 11 is an RF detection amplifier that has a function of varying the amplification degree according to the output of the IF detector 12, when the output voltage of the IF detector 12 is high. In this case, the amplification degree of the RF detection amplifier 11 is made equal to that of the conventional example, and when the output voltage of the IF detector 12 is low, the amplification degree is made lower than that of the conventional example.

The RF detection amplifier 11 has an input capacitance C1.
, Three resistors R1, R2, R3, two NPN transistors Q1, Q2, a bias voltage source Vr1, and NP
A differential amplifier 11a composed of an N-transistor Q3 and an amplification degree thereof is two PNP transistors Q.
4, Q5, bias voltage source Vr2, reference current source Io
11 and a variable current source 11 including a diode D1
It is changed by the base voltage input of the PNP transistor Q5 of b.

The IF detector 12 is composed of a rectifying diode D121, a detecting capacitor C121, and a time constant setting resistor R121.

FIG. 2 shows the spectrum of each part when a relatively strong desired wave signal and strong interference wave that can be sufficiently received from the antenna 1 are simultaneously input in one embodiment of the AM radio receiver of this embodiment. 2 is shown in FIG.
(A) is an input of the antenna 1, D is a desired wave, U is an interfering wave, FIG. 2 (b) is an output spectrum of the RF amplifier 3, FIG. 2 (c) is a frequency characteristic of the RF tuner 4, Figure 2
(D) shows the input spectrum of the mixer 6. Thus, when the desired wave signal level is high, the output level of the BPF 7 is also high, and the amplification degree of the RF detection amplifier 11 is the same as that of the RF detection amplifier 13 of the conventional example.

The desired wave signal and the interfering wave input as shown in FIG. 2 (a) are processed in the same manner as in the conventional example by the wide band AGC loop constituted by the RF detection amplifier 11, the RF detector 9 and the attenuator 2. Is attenuated by the attenuator 2 so as not to exceed a certain level X shown in FIG.
The output spectrum of the F amplifier 3 is as shown in FIG. The RF tuner 4 is centered around the desired wave signal frequency, as shown in FIG.
Since it has the bandpass characteristic shown in (c), the output spectrum of the RF tuner 4 is as shown in FIG. 2 (d). Thus, the level of the interfering wave U is controlled by the action of the wide band AGC loop, so that the level of the interfering wave input to the mixer 6 is limited to a certain level or less. Therefore, like the conventional example, the mixer 6
It is possible to prevent interference of the interference wave modulation signal with the desired wave due to the non-linearity of.

FIG. 3 shows the spectrum of each part when a weak desired wave signal and a strong interfering wave are simultaneously input from the antenna 1 in one embodiment of the AM radio receiver of this embodiment. (A) is an input of the antenna 1, D is a desired wave, U is an interfering wave, and FIG.
3 (c) shows the frequency characteristic of the RF tuner 4, and FIG. 3 (d) shows the input spectrum of the mixer 6. When the desired wave signal level is low as described above, the output level of the BPF 7 is also low and the amplification degree of the RF detection amplifier 11 is the RF detection amplifier 13 of the conventional example.
It is lower than the amplification degree of. Therefore, broadband AG
The limit level of the C loop becomes higher, and the limit level Y shown in FIG. 2 (b) is higher than the conventional limit level X shown in FIG. 6 (b). Therefore, the output spectrum of the RF tuner 4 is as shown in FIG. 2D, and the level of the desired wave signal is higher than that of the conventional one. FIG. 4 shows the output of the AM demodulator 8 in the state of FIG. 3, and shows that good reception sensitivity can be obtained without unnecessarily lowering the sensitivity to the desired wave signal as compared with the conventional case.

When the desired wave signal is larger than the interfering wave, the output level of the MIX input AGC amplifier 10 becomes higher than the output level of the RF detection amplifier 11, so that the RF detector 9 uses the MIX. The output level of the input AGC amplifier 10 is detected, and this detection level is set level X.
The attenuation amount of the attenuator 2 is controlled so as not to exceed the above. As a result, both the desired wave signal and the disturbing wave are attenuated, and the disturbing wave is suppressed to a small extent by the selection characteristic of the RF tuner 4, so that the desired wave signal is received with a high S / N ratio.

[0034]

As described above, according to the radio receivers of the first and second aspects of the present invention, the IF detector for detecting the intermediate frequency signal level is provided, and the output level of the IF detector is set. In the case where a weak desired wave signal is received when the interfering wave is strong by changing the amplification degree of the RF detection amplifier according to the above, the loop gain of the AGC is reduced to reduce the attenuation amount of the input signal by the attenuator. Since it has been reduced, it is possible to suppress the interfering wave without losing the desired wave signal.
M radio receiver can be realized.

In the radio receiver according to the third aspect of the present invention, when the desired wave signal is larger than the interfering wave, since the AGC amplifier is provided as in the conventional case, the desired wave signal and the interfering wave are combined. Both can be attenuated and the interfering wave can be suppressed small by the selection characteristic of the RF tuner to receive the desired wave signal with a high S / N ratio.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an AM radio receiver according to an embodiment of the present invention.

FIG. 2 is a diagram showing a spectrum of each block when a desired wave is relatively strong in an embodiment of the present invention.

FIG. 3 is a diagram showing a spectrum of each block when a desired wave is weak in one embodiment of the present invention.

FIG. 4 is a diagram showing an output of an AM demodulator when a desired wave is weak according to an embodiment of the present invention.

FIG. 5 is a block diagram showing a conventional AM radio receiver.

FIG. 6 is a diagram showing a spectrum of each block when a desired wave is relatively strong in a conventional AM radio receiver.

FIG. 7 is a diagram showing a spectrum of each block when a desired wave is weak in a conventional AM radio receiver.

FIG. 8 is a diagram showing an output of an AM demodulator when a desired wave is weak in a conventional AM radio receiver.

[Explanation of symbols]

 1 antenna 2 attenuator 3 RF amplifier 4 RF tuner 5 local oscillator 6 mixer 7 BPF 8 AM demodulator 9 RF detector 10 MIX input AGC amplifier 11 RF detection amplifier 11a differential amplifier 11b variable current source 12 IF detection vessel

Claims (3)

[Claims] 1. An attenuator that varies the amount of attenuation of an antenna input signal by a control voltage, an RF amplifier that amplifies the output of the attenuator, an RF tuner that extracts a desired wave signal from the output of the RF amplifier, and A mixer that converts the output of the RF tuner into an intermediate frequency signal by mixing with the local oscillation output, a bandpass filter that extracts an intermediate frequency signal component from the output of the mixer, and an intermediate frequency signal that has passed through the bandpass filter. And an IF detector that detects the output level of the bandpass filter and an output signal of the RF amplifier, the amplification degree of which is controlled according to the output of the IF detector. An RF detection amplifier and an output level of the RF detection amplifier,
A radio receiver comprising an RF detector which gives the detected output as the control voltage to the attenuator. 2. The amplification factor of the RF detection amplifier is controlled to be large when the output of the IF detector is large and to be small when the output of the IF detector is small.
The radio receiver described. 3. An AGC amplifier for amplifying the output of the RF tuner and outputting the amplified signal to the RF detector,
The RF detector detects the higher one of the output level of the RF detection amplifier and the output level of the AGC amplifier, and supplies the detected output to the attenuator as a control voltage. The radio receiver according to claim 1 or 2.