JPH08288879A - Agc circuit for up-conversion receiver - Google Patents

Abstract

PURPOSE: To prevent erroneous stoppage in case of a search against the interfer ence of an adjacent broadcasting station. CONSTITUTION: This AGC circuit of an up-conversion receiver for up-converting a received high frequency is provided with a wide band AGC circuit 13 for performing AGC to a high frequency stage based on high frequency signals, a middle band AGC circuit 14 for performing the AGC to the high frequency stage along with the wide band AGC circuit 13 based on first intermediate frequency signals for which the high frequency is up-converted and a narrow band AGC circuit 16 for performing the AGC before and after down conversion based on second intermediate frequency signals for which the frequency of the first intermediate frequency signals is down-converted. The wide band AGC circuit 13 performs the AGC to the high frequency stage based on the synthetic signals of the high frequency signals and the second intermediate frequency signals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AGC (Automatic Gain Control) circuit for an upconversion receiver,
Particularly, the present invention relates to an AGC circuit that prevents an erroneous stop during a search.

[0002]

2. Description of the Related Art FIG. 4 is a diagram for explaining an AGC circuit of a conventional up-conversion receiver. The up-conversion receiver shown in this figure has a frequency of 530 to 1700 kHz.
An antenna 1 for inputting an AM (Amplitude Modulation) broadcast wave of z, a radio frequency amplifier (RFAMP) 2 for amplifying a received radio frequency signal, and a frequency 10.7M from the frequency 530 to 1700 kHz connected to the radio frequency amplifier 2.
1st mixer 3 (1
sMix), a first intermediate filter 4 (1 stiF filter) that is connected to the first mixer 3 and extracts only a signal having a frequency of 10.7 kHz after mixing, and amplifies the signal extracted by the first intermediate filter 4. The amplifier (AMP) 5 and the amplified signal with a frequency of 10.7 MHz by the amplifier 5 are
Second mixer 6 for down conversion to kHz
(2ndMix), a second intermediate filter (2ndiF filter) 7 that is connected to the second mixer 6 and extracts only a signal having a frequency of 450 kHz after mixing, and an amplifier that amplifies the signal extracted by the second intermediate filter 7. (AMP) 8
A detector (DET) 9 for detecting the amplified signal from the amplifier 8 and using it for reproduction; a local oscillator 10 for supplying the first mixer 3 with a signal having a frequency of 10.7 MHz + a reception frequency; The frequency of the oscillator 10 can be made variable, another broadcasting station is searched, and the search unit 11 that stops the search when the reception level becomes a certain level, and the detector 9
And a level detector 12 for detecting the level of the detection signal by and supplying the reception level to the search unit. Here, in the search unit 11, for example, the frequency of the local oscillator 10 is made variable every 9 kHz. Further, the up-conversion receiver is an AGC circuit that prevents the output signal from level fluctuation even if the level of the received signal fluctuates, and makes the gain of the high frequency amplifier 2 variable based on the output level of the high frequency amplifier 2. A wide band AGC circuit 13 having a wide band AGC sensitivity, a middle band AGC circuit 14 having a middle band AGC sensitivity for varying the gain of the high frequency amplifier 2 based on the output signal of the first intermediate filter 4, and a wide band. The output of the AGC circuit 13 and the mid-band AGC circuit 14 is combined to make the gain of the high frequency amplifier 2 variable, and the second mixer 6 and the amplifier 8 based on the output level of the detector 9. And a narrow band AGC circuit 16 having a narrow band AGC sensitivity that makes the gain variable.

FIG. 5 is a diagram for explaining the AGC sensitivity of the wide band AGC circuit 13, the middle band AGC circuit 14 and the narrow band AGC circuit 16 of FIG. As shown in this figure, wideband AG
Regarding the AGC sensitivities of the C circuit 13, the middle band AGC circuit 14, and the narrow band AGC circuit 16, the sensitivity widths become narrower in this order, and the maximum value of the sensitivity is reversed in this order. here,
High sensitivity means that the AGC operates quickly, that is,
To operate the AGC at a low level of the received signal,
Low sensitivity means that the AGC operates slowly, that is,
It means operating the AGC at a high level of the received signal.
For example, in the narrow band AGC circuit 16, the sensitivity becomes maximum at 450 kHz, and the AGC operation becomes the fastest, but when the frequency to be synchronized is deviated, these sensitivities become small.
The operation of the GC becomes slow. That is, when synchronized, the narrow band AGC circuit 16 operates at a low reception level.
Operates, but the operation is fast, but if synchronization is not yet achieved, such as during search, the gain to be set is large and the AG
C sensitivity is low and operation is slow.

[0004]

However, in the AGC circuit of the conventional up-conversion receiver, when the reception frequency changes during a search or the like, signal jamming occurs when the radio wave level from the adjacent broadcasting station is very high. Occurs. In this case, since the sensitivity of the narrow band AGC circuit 16 is small, there is no AGC operation due to the delay, and a high signal waveform is input to the second mixer 6. This signal waveform is distorted by the second mixer 6, and harmonics are generated in the AM modulation signal. For example, harmonics of 3 kHz × 3 = 9 kHz for a modulation signal of 3 kHz and 4.5 kHz × 2 = 9 kHz for a modulation signal of 4.5 kHz are generated. Therefore, the narrow band AGC circuit 16
There is a problem that the level detector 12 operates and the search unit 11 determines that a broadcasting station is detected before the AGC operation by the, and the search is erroneously stopped. In this case, it is possible to increase the range of use so that the signal waveform is not distorted in the second mixer 6, but since the second mixer 6 is usually incorporated in the IC circuit, It is difficult to change by itself, and the change causes a cost problem.

In addition, the wide band AGC circuit 13 and the medium band AG
Although such a problem can be dealt with by increasing the sensitivity of the C circuit 14 and accelerating the AGC operation, the AGC operation to the reception frequency at the time of synchronization is also accelerated, resulting in S / N.
A new problem that is worse. Therefore,
The present invention has been made in view of the above problems, and an object thereof is to provide an AGC circuit of an up-conversion receiver capable of preventing an erroneous stop due to interference of an adjacent broadcast station at the time of search.

[0006]

In order to solve the above problems, the present invention provides an AGC circuit of an upconversion receiver having the following configuration. That is, in the first aspect of the present invention, the wide band AGC for applying AGC to the high frequency stage based on the high frequency signal in the AGC circuit of the up conversion receiver for up converting the received high frequency.
A circuit, a middle-band AGC circuit for applying AGC to a high-frequency stage together with the wide-band AGC circuit based on the first intermediate-frequency signal obtained by up-converting the high frequency, and a second down-conversion of the frequency of the first intermediate-frequency signal. AG before and after down conversion based on the intermediate frequency signal of
A narrow band AGC circuit for multiplying C is provided. The wide band AGC circuit applies AGC to a high frequency stage based on a combined signal of the high frequency signal and the second intermediate frequency signal.

The middle band AGC circuit applies AGC to the high frequency stage together with the wide band AGC circuit based on a combined signal of the first intermediate frequency signal and the second intermediate frequency signal which up-converts the high frequency. Good. In the second invention, the AGC circuit of the up-conversion receiver that up-converts the received high frequency,
A wide band AGC circuit for applying AGC to a high frequency stage based on the high frequency signal; a medium band AGC circuit for applying AGC to the high frequency stage together with the wide band AGC circuit based on the first intermediate frequency signal that up-converts the high frequency; A narrow band AGC circuit is provided for performing AGC before and after down conversion based on the second intermediate frequency signal obtained by down converting the frequency of the first intermediate frequency signal. The wide band AGC circuit applies AGC to a high frequency stage based on a combined signal of the high frequency signal and the first intermediate frequency signal.

The wide band AGC circuit may apply AGC to a high frequency stage based on a composite signal of the high frequency signal and the second intermediate frequency signal passed through a low pass filter. The wideband AGC circuit may apply AGC to a high frequency stage based on a composite signal of the high frequency signal and the first intermediate frequency signal passed through a low pass filter.

[0009]

Operation: AGC of the up-conversion receiver of the present invention
According to the circuit, the wide band AGC circuit applies an AGC to the high frequency stage based on the composite signal of the high frequency signal and the second intermediate frequency signal, thereby erroneously stopping the interference of the adjacent broadcasting station during the search. Can be prevented and S / N can be secured. The middle-band AGC circuit applies AGC to the high-frequency stage together with the wide-band AGC circuit on the basis of a composite signal of the first intermediate-frequency signal and the second intermediate-frequency signal obtained by up-converting the high-frequency, so that a larger adjacent signal is obtained. Effective for obstructing broadcasting stations.

Further, the wide band AGC circuit applies AGC to the high frequency stage based on the composite signal of the high frequency signal and the first intermediate frequency signal, thereby similarly preventing interference from an adjacent broadcasting station at the time of searching. Accidental stop can be prevented and S / N
Can be secured. The wideband AGC circuit applies AGC to a high frequency stage based on a composite signal of the high frequency signal and the second intermediate frequency signal that has passed through a low pass filter, thereby preventing an AGC malfunction due to an unnecessary signal.
The wideband AGC circuit applies AGC to a high frequency stage based on a composite signal of the high frequency signal and the first intermediate frequency signal that has passed through a low pass filter, thereby preventing an AGC malfunction due to an unnecessary signal.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an AGC circuit of an upconversion receiver according to a first embodiment of the present invention. In this figure, the configuration different from that of FIG. 4 is such that the output of the second mixer 6 is connected to the wide band AGC circuit 13, and an RC type low pass filter is provided between the second mixer 6 and the wide band AGC circuit 13. (LPF) 17 is provided. Where broadband A
The GC circuit 13 has a wide band AGC sensitivity for varying the gain of the high frequency amplifier 2 based on the combined signal of the output signal of the high frequency amplifier 2 and the output signal of the second mixer 6. In this way, the adjacent broadcasting stations (for example, 9 kHz
Narrowband AGC if signals from
Since the circuit 16 does not operate, the input signal to the second mixer 6 becomes large, but this signal is added to the wide band AGC circuit 13 and the gain of the high frequency amplifier 2 is suppressed.
It is possible to suppress the level change after the mixer 6 and to prevent the occurrence of distortion and the false stop of the search. At the time of normal synchronized reception, the signal level of the second mixer 6 can be suppressed to a certain level or less by the narrow band AGC circuit 16, so that the wide band AGC circuit 13 according to the present embodiment does not operate and the S / N is not deteriorated. It won't happen. In this way, search erroneous stop prevention and S /
It becomes possible to achieve both of securing N.

In this case, the low pass filter 17 makes it possible to prevent the wide band AGC circuit 13 from malfunctioning due to another signal leakage (for example, the first intermediate filter 4 or the like). FIG. 2 is a diagram showing a modification of the first embodiment of the present invention. As shown in the figure, the output signal of the low pass filter 7 is also supplied to the middle band AGC circuit 14. here,
In addition, the middle band AGC circuit 14 includes the first intermediate filter 4
Of the intermediate frequency band A for varying the gain of the high frequency amplifier 2 based on the combined signal of the output signal of the second mixer 6 and the output signal of the second mixer 6.
Has GC sensitivity. In this way, with respect to the interference of a larger adjacent broadcasting station, the change in level after the second mixer 6 is further suppressed than that in the first embodiment, so that the occurrence of distortion and the false stop of the search can be prevented. It can be prevented.

FIG. 3 is a diagram showing an AGC circuit of an upconversion receiver according to the second embodiment of the present invention. In this figure, the configuration different from that of FIG. 5 is such that the output of the amplifier 5 is connected to the wideband AGC circuit 13, and the amplifier 5 and the wideband AGC are connected.
An RC type low pass filter 17 is provided between the circuit 13 and the circuit 13. Here, the wide band AGC circuit 13 has wide band AGC sensitivity for varying the gain of the high frequency amplifier 2 based on the combined signal of the output signal of the high frequency amplifier 2 and the output signal of the amplifier 5. In this way, when a signal from an adjacent broadcasting station exists at the time of search, the narrow band AGC is performed.
Since the circuit 16 does not operate, the input signal to the second mixer 6 becomes large, but this signal is added to the wide band AGC circuit 13 and the gain of the high frequency amplifier 2 is suppressed.
It is possible to suppress the level change after the mixer 6 and to prevent the occurrence of distortion and the false stop of the search. At the time of normal synchronized reception, the signal level of the second mixer 6 can be suppressed to a certain level or less by the narrow band AGC circuit 16, so that the wide band AGC circuit 13 does not operate and the S / N is deteriorated also in this embodiment. Does not happen. In this way, it is possible to achieve both prevention of false stoppage of search and securing of S / N.

Also in this case, the low pass filter 17 is
It is possible to prevent the wideband AGC circuit 13 from malfunctioning due to another signal leakage (for example, the first intermediate filter 4 or the like).

[0015]

As described above, according to the AGC circuit of the up-conversion receiver of the present invention, the wide band AGC is provided.
Since the circuit applies AGC to the high-frequency stage based on the composite signal of the high-frequency signal and the second intermediate-frequency signal, it is possible to prevent erroneous stoppage due to interference from adjacent broadcasting stations during search and to secure S / N. become. The mid-band AGC circuit applies AGC to the high-frequency stage together with the wide-band AGC circuit based on the combined signal of the first intermediate frequency signal and the second intermediate frequency signal that up-converts the high frequency. effective. The wide band AGC circuit has a high frequency signal and a first signal.
By applying AGC to the high-frequency stage based on the combined signal with the intermediate frequency signal of (1), it is possible to prevent erroneous stop due to interference of the adjacent broadcasting station and secure S / N in the same manner during search. The wideband AGC circuit applies AGC to the high-frequency stage based on the composite signal of the high-frequency signal and the second intermediate-frequency signal that has passed through the low-pass filter, thus preventing AGC malfunction due to unnecessary signals. Since the wideband AGC circuit applies AGC to the high frequency stage based on the composite signal of the high frequency signal and the first intermediate frequency signal that has passed through the low pass filter, it prevents AGC malfunction due to unnecessary signals.

[Brief description of drawings]

FIG. 1 is a diagram showing an AGC circuit of an upconversion receiver according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a modification of the first embodiment of the present invention.

FIG. 3 is a diagram showing an AGC circuit of an upconversion receiver according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating an AGC circuit of a conventional up-conversion receiver.

5 is a diagram illustrating AGC sensitivities of the wide band AGC circuit 13, the middle band AGC circuit 14, and the narrow band AGC circuit 16 of FIG.

[Explanation of symbols]

 13 ... Wide band AGC 14 ... Medium band AGC 16 ... Narrow band AGC 17 ... Low pass filter

Claims (5)

[Claims] 1. An AGC circuit of an up-conversion receiver that up-converts a received high frequency, a wide band AGC circuit (13) for applying AGC to a high-frequency stage based on the high-frequency signal, and a first up-converted high frequency. Based on an intermediate frequency AGC circuit (14) for applying AGC to a high frequency stage together with the wide band AGC circuit (13) based on the intermediate frequency signal, and a second intermediate frequency signal down-converting the frequency of the first intermediate frequency signal. And a narrow band AGC circuit (16) for applying AGC before and after down conversion, wherein the wide band AGC circuit (13) sets a high frequency stage based on a composite signal of the high frequency signal and the second intermediate frequency signal. A
An AGC circuit of an up-conversion receiver characterized by applying GC. 2. The medium band AGC circuit (14), together with the wide band AGC circuit (13), generates a high frequency signal based on a combined signal of the first intermediate frequency signal obtained by up-converting the high frequency signal and the second intermediate frequency signal. The AGC circuit of the up-conversion receiver according to claim 1, wherein AGC is applied to the stage. 3. An AGC circuit of an up-conversion receiver for up-converting a received high frequency, a wide band AGC circuit (13) for applying AGC to a high-frequency stage based on the high-frequency signal, and a first up-converted high frequency. Based on an intermediate frequency AGC circuit (14) for applying AGC to a high frequency stage together with the wide band AGC circuit (13) based on the intermediate frequency signal, and a second intermediate frequency signal down-converting the frequency of the first intermediate frequency signal. And a narrow band AGC circuit (16) for applying AGC before and after down conversion, wherein the wide band AGC circuit (13) sets a high frequency stage based on a combined signal of the high frequency signal and the first intermediate frequency signal. A
An AGC circuit of an up-conversion receiver characterized by applying GC. 4. The wide band AGC circuit (13) is arranged in a high frequency stage based on a composite signal of the high frequency signal and the second intermediate frequency signal passed through a low pass filter (17).
The AGC circuit of the up-conversion receiver according to claim 1, wherein 5. The wide band AGC circuit (13) is arranged in a high frequency stage based on a composite signal of the high frequency signal and the first intermediate frequency signal passed through a low pass filter (17).
The AGC circuit of the up-conversion receiver according to claim 3, wherein