JP3093125B2 - AGC circuit of up-conversion receiver - Google Patents

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 up-conversion receiver.
In particular, the present invention relates to an AGC circuit for preventing 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 the figure has a frequency of 530 to 1700 kHz.
An antenna 1 for inputting AM (Amplitude Modulation) broadcast radio waves, a high-frequency amplifier (RFAMP) 2 for amplifying a received high-frequency signal, and a high-frequency amplifier 2 connected to the high-frequency amplifier 2 from the frequency of 530 to 1700 kHz to a frequency of 10.7 M
1st mixer 3 (1
sMix), a first intermediate filter 4 (1 stiF filter) connected to the first mixer 3 and extracting only a signal having a frequency of 10.7 kHz after mixing, and amplifying the signal extracted by the first intermediate filter 4. An amplifier (AMP) 5 and an amplified signal having a frequency of 10.7 MHz
Second mixer 6 for down-conversion to kHz
(2ndMix), a second intermediate filter (2ndiF filter) 7 connected to the second mixer 6 for extracting only a signal having a frequency of 450 kHz after mixing, and an amplifier for amplifying a signal extracted by the second intermediate filter 7 (AMP) 8
A detector (DET) 9 for detecting an amplified signal from the amplifier 8 and using the signal for reproduction; a local oscillator 10 for supplying a signal of a frequency of 10.7 MHz + a receiving frequency to the first mixer 3; A search section 11 for changing the frequency of the oscillator 10 to search another broadcasting station and stopping the search when the reception level becomes a certain level;
And a level detector 12 for detecting the level of the detection signal and supplying the reception level to the search unit. Here, the search unit 11 makes the frequency of the local oscillator 10 variable every 9 kHz, for example. Further, the up-conversion receiver varies the gain of the high-frequency amplifier 2 based on the output level of the high-frequency amplifier 2 as an AGC circuit that prevents the output signal from fluctuating even if the level of the received signal changes. 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, A synthesizing unit 15 for synthesizing output signals of the AGC circuit 13 and the mid-band AGC circuit 14 to vary the gain of the high-frequency amplifier 2, and a second mixer 6 and an amplifier 8 based on the output level of the detector 9. A narrow-band AGC circuit 16 having a narrow-band AGC sensitivity for varying the gain.

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 FIG.
The AGC sensitivities of the C circuit 13, the middle band AGC circuit 14 and the narrow band AGC circuit 16 have narrower sensitivity widths in these order, and the maximum values of the sensitivities are reversed in this order. here,
High sensitivity means that AGC operation is fast, that is,
Operating the AGC at a low level of the received signal,
Low sensitivity means that AGC operation is slow, that is,
This refers to 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 operation of the AGC becomes the fastest. However, when the frequency to be synchronized deviates, these sensitivities decrease, and A
The operation of the GC becomes slow. That is, when synchronization is established, the narrow band AGC circuit 16 performs AGC at a low reception level.
Operates and operates quickly, but when synchronization is not yet established as during a search, the gain to be set is large and 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, or when the level of the radio wave from an adjacent broadcasting station is very large, signal interference may occur. 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 a harmonic is generated in the AM modulation signal. For example, for a 3 kHz modulated signal, 3 kHz × 3 = 9 kHz, and for a 4.5 kHz modulated signal, 4.5 kHz × 2 = 9 kHz harmonics are generated. Therefore, the narrow band AGC circuit 16
Prior to the AGC operation, there is a problem that the level detector 12 operates and the search unit 11 determines that a broadcast station has been detected and erroneously stops the search. In this case, it is possible to widen 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 an IC circuit, It is difficult to change by itself, and there is a cost problem with changing.

A wide band AGC circuit 13 and a medium band AG
By increasing the sensitivity of the C circuit 14 and speeding up the AGC operation, such a problem can be dealt with. However, the AGC operation to the reception frequency at the time of synchronization also speeds up, and as a result, S / N
A new problem arises that is worse. Therefore,
An object of the present invention is to provide an AGC circuit of an up-conversion receiver that can prevent an erroneous stop due to interference of an adjacent broadcast station during a search in view of the above problems.

[0006]

According to the present invention, there is provided an AGC circuit of an up-conversion receiver having the following structure to solve the above-mentioned problems. That is, in the first invention, a wideband AGC for applying AGC to a high-frequency stage based on the high-frequency signal in an AGC circuit of an up-conversion receiver for up-converting a received high frequency.
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 signal; and a second-band AGC circuit for down-converting the frequency of the first intermediate-frequency signal. Before and after down conversion based on the intermediate frequency signal of
And a narrow band AGC circuit for applying C. 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.

The middle band AGC circuit applies AGC to a high frequency stage together with the wide band AGC circuit based on a composite signal of the first intermediate frequency signal and the second intermediate frequency signal obtained by up-converting the high frequency. Is also good. In the second invention, an AGC circuit of an up-conversion receiver for up-converting a received high frequency wave includes:
A wide-band AGC circuit for applying AGC to a high-frequency stage based on the high-frequency signal; a middle-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 obtained by up-converting the high frequency; A narrow-band AGC circuit for applying 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 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.

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 via 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 via a low pass filter.

[0009]

AGC of the up-conversion receiver of the present invention
According to the circuit, the broadband 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, thereby erroneously stopping an adjacent broadcast station during a search. Can be prevented and S / N can be secured. The mid-band AGC circuit applies AGC to the high-frequency stage together with the wide-band AGC circuit based on a composite signal of the first intermediate frequency signal and the second intermediate frequency signal obtained by up-converting the high frequency, thereby providing a larger adjacent frequency. It is effective for interference from broadcasting stations.

Further, 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. Incorrect 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 via a low-pass filter, thereby preventing an AGC malfunction due to an unnecessary signal.
The wideband AGC circuit applies an AGC to a high frequency stage based on a composite signal of the high frequency signal and the first intermediate frequency signal via 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 up-conversion receiver according to a first embodiment of the present invention. 4 is different from FIG. 4 in that the output of the second mixer 6 is connected to the wideband AGC circuit 13 and an RC type low-pass filter is provided between the second mixer 6 and the wideband AGC circuit 13. (LPF) 17 is provided. Here, broadband A
The GC circuit 13 has a wide-band AGC sensitivity for varying the gain of the high-frequency amplifier 2 based on a composite 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 broadcast station (for example, 9 kHz
z away), the narrowband AGC
Since the circuit 16 does not operate, the input signal to the second mixer 6 increases, but this signal is added to the wideband AGC circuit 13 to suppress the gain of the high-frequency amplifier 2, resulting in the second signal.
The change in the level after the mixer 6 can be suppressed to prevent distortion and erroneous stop of the search. At the time of ordinary 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 deterioration of S / N is reduced. Does not happen. In this way, search error stop prevention and S /
N can be ensured at the same time.

In this case, the low-pass filter 17 makes it possible to prevent the wide band AGC circuit 13 from malfunctioning due to other 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,
Further, the middle band AGC circuit 14 includes the first intermediate filter 4.
And a middle band A for varying the gain of the high-frequency amplifier 2 based on the output signal of the second mixer 6 and the composite signal of 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 the level after the second mixer 6 is further suppressed more than in the first embodiment, so that the occurrence of distortion and the erroneous stop of the search are prevented. Can be prevented.

FIG. 3 is a diagram showing an AGC circuit of an up-conversion receiver according to a second embodiment of the present invention. 5 is different from FIG. 5 in that the output of the amplifier 5 is connected to the wideband AGC circuit 13 and the amplifier 5 and the wideband AGC
An RC type low-pass filter 17 is provided between the circuit 13 and the circuit 13. Here, the wideband AGC circuit 13 has a wideband AGC sensitivity for varying the gain of the high frequency amplifier 2 based on a composite signal of the output signal of the high frequency amplifier 2 and the output signal of the amplifier 5. In this way, when there is a signal from an adjacent broadcast station at the time of search, the narrow band AGC
Since the circuit 16 does not operate, the input signal to the second mixer 6 increases, but this signal is added to the wideband AGC circuit 13 to suppress the gain of the high-frequency amplifier 2, and as a result, the second
The change in the level after the mixer 6 can be suppressed to prevent distortion and erroneous stop of the search. At the time of ordinary 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 even in this embodiment, the wide-band AGC circuit 13 does not operate, and the S / N deteriorates. Does not happen. In this way, it is possible to achieve both prevention of erroneous search stoppage and securing of S / N.

Also in this case, the low-pass filter 17
This makes it possible to prevent the wide band AGC circuit 13 from malfunctioning due to other 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 wideband AGC
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, so that it is possible to prevent an erroneous stop from interference by an adjacent broadcast station 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 a composite signal of the first intermediate frequency signal and the second intermediate frequency signal obtained by up-converting the high frequency. effective. The wideband AGC circuit is used for the high frequency signal and the first signal.
AGC is applied to the high-frequency stage based on the composite signal with the intermediate frequency signal, so that an erroneous stop can be prevented and an S / N ratio can be secured in the same manner with respect to interference of an adjacent broadcasting station during a search. The wide band AGC circuit applies AGC to the high frequency stage based on a composite signal of the high frequency signal and the second intermediate frequency signal passed through the low pass filter, thereby preventing AGC malfunction due to unnecessary signals. The wideband AGC circuit applies AGC to the high frequency stage based on a composite signal of the high frequency signal and the first intermediate frequency signal passed through the low pass filter, thereby preventing AGC malfunction due to unnecessary signals.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an AGC circuit of an up-conversion 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 illustrating an AGC circuit of an up-conversion 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 broadband AGC 14 middle band AGC 16 narrow band AGC 17 low-pass filter

Claims (5)

(57) [Claims] An AGC circuit of an up-conversion receiver for up-converting a received high-frequency signal, comprising: a wide-band AGC circuit (13) for applying AGC to a high-frequency stage based on the high-frequency signal; A middle band AGC circuit (14) for applying AGC to a high frequency stage together with the wide band AGC circuit (13) based on an intermediate frequency signal; and a second intermediate frequency signal obtained by down-converting the frequency of the first intermediate frequency signal. A narrow-band AGC circuit (16) for applying AGC before and after down-conversion, and the wide-band AGC circuit (13) is connected to 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) based on a composite signal of the first intermediate frequency signal and the second intermediate frequency signal obtained by up-converting the high frequency. The AGC circuit of an up-conversion receiver according to claim 1, wherein the stage is subjected to AGC. 3. An AGC circuit of an up-conversion receiver for up-converting a received high-frequency signal, comprising: a wide-band AGC circuit (13) for applying AGC to a high-frequency stage based on the high-frequency signal; A middle band AGC circuit (14) for applying AGC to a high frequency stage together with the wide band AGC circuit (13) based on an intermediate frequency signal; and a second intermediate frequency signal obtained by down-converting the frequency of the first intermediate frequency signal. A narrow-band AGC circuit (16) for applying AGC before and after down-conversion, and the wide-band AGC circuit (13) is connected to a high-frequency stage based on a composite 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 wideband AGC circuit (13) performs an AGC on a high frequency stage based on a composite signal of the high frequency signal and the second intermediate frequency signal via a low pass filter (17).
The AGC circuit of the up-conversion receiver according to claim 1, wherein the AGC circuit is applied. 5. The wideband AGC circuit (13) performs AGC on a high frequency stage based on a composite signal of the high frequency signal and the first intermediate frequency signal via a low pass filter (17).
The AGC circuit of the up-conversion receiver according to claim 3, wherein the AGC circuit is applied.