JP2962380B2 - Receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving apparatus used for receiving FM stereo broadcast waves and the like, and more particularly to a receiving apparatus which is hardly affected by interference such as intermodulation and capable of receiving signals with high sensitivity.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory diagram for explaining intermodulation interference in FM reception. As is well known, when there is a broadcast wave having a frequency of f1 and a frequency of f2, ｛(2 ×
f1) -f2}, an intermodulation interference wave of frequency f3 is generated. When the frequency f0 of the desired selected station is close to or the same as the frequency f3 of the intermodulation interference wave, intermodulation interference occurs. If the input level of the desired selected station of f0 to the tuner is high, the input of the desired selected station is prioritized by the capture ratio, but the received sound quality is still affected, and the input intensity of the intermodulation interference wave is reduced. If the input level is higher than the input level, a beat or the like occurs.

[0003]

As a countermeasure against the above-mentioned intermodulation interference, it is conceivable to provide selectivity to the input of the frequency mixer. However, by further controlling the gain at the front end, the RF stage can be controlled. It is conceivable to prevent the amplification gain from increasing. However, if the amplification gain of the front end is suppressed due to intermodulation interference, the reception device will have poor sensitivity as a whole, for example, when intermodulation interference does not occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and has as its object to provide a receiving apparatus which can always perform optimal reception, prevents the above-mentioned intermodulation interference, and has high sensitivity. And

[0005]

According to the present invention, there is provided a receiving apparatus for outputting a first intermediate frequency signal from a received signal.
Front end and the first front end
A first intermediate frequency signal having a high reception sensitivity from the reception signal;
Output a second intermediate frequency signal of greater intensity than
2 front ends and frequency based on intermod
When the deviation is larger than the frequency deviation during normal reception
A leo pilot signal is detected from the second intermediate frequency signal.
Intermodulation detector that detects intermodulation interference by emitting
Intermodulation interference is not detected by the intermodulation detection unit.
Output the second intermediate frequency signal to the stereo demodulation unit.
And when the intermodulation interference is detected,
Switching to output the intermediate frequency signal of 1 to the stereo demodulator
And means are provided.

In the above, for example, the first fluorocarbon
And the second front end amplifies the received signal.
And an RF amplifier according to the intermediate frequency signal.
An automatic gain control unit for controlling the amplification gain of the F-amplifier
And the automatic gain control unit in the first front end.
The intensity of the input signal subjected to automatic gain control by
Automatic gain by the automatic gain control unit at the front end
If the control is set lower than the input signal strength
It is.

[0007]

In the above means, the reception output is obtained while fixing the selection of the output from a specific front end during reception or selecting and switching the output from a plurality of front ends. Then, when, for example, intermodulation interference is detected by an output from a certain front end, a front end having characteristics that hardly cause this interference is selected.

[0008] Specifically, the reception output is usually obtained while selecting the reception output from the front end having high reception sensitivity or selecting the reception output from a plurality of front ends. When a pilot signal of an interfering wave is detected by the output detection unit based on the reception output from the front end having high reception sensitivity, the front end to be selected is fixed to the front end having low reception sensitivity, and the influence of intermodulation interference is obtained. Less. Then, when the interference signal pilot signal is no longer detected, the reception output from the front end with high reception sensitivity is selected, or the reception output from a plurality of front ends is switched to select the optimum reception output. .

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram showing an example of a receiving apparatus for receiving an FM stereo broadcast wave as an embodiment of the present invention.
Is a circuit block diagram of the front end (F / E) shown in FIG. 1, and FIG. 3 is a diagram showing output characteristics of each front end. The receiving apparatus shown in FIG. 1 is provided with a first front end (F / E) 1 and a second front end (F / E) 2 having different receiving characteristics. Each of the front ends 1 and 2 has an FM detection circuit 3 and 4
Is connected. The detection output from the FM detection circuit 3 or the detection output from the FM detection circuit 4 is supplied to a switching unit (SW) 5.
And demodulated by a first stereo demodulation circuit (multiplex (MPX) decoder) 7 through a noise removal circuit 6 such as a limiter, and demodulated outputs of L channel and R channel are obtained.

The detection output from the second FM detection circuit 4 is input to a second stereo demodulation circuit 8. Here, the first stereo demodulation circuit 7 performs normal stereo demodulation on the reception output switched by the switching unit 5, while the second stereo demodulation circuit 8 receives the reception output by the second front end 2. It functions as an output detection unit for detecting a pilot signal due to intermodulation interference from the detection output detected by the FM detection circuit 4. The detection operation by the second stereo demodulation circuit 8 as the output detection unit is monitored by a control unit 9 such as a microcomputer, and the switching unit 5 is switched by an instruction from the control unit 9.

Further, detection outputs from the respective FM detection circuits 3 and 4 are input to a diversity switching unit 15.
In the diversity switching unit 15, the reception intensity of the reception output from the first or second front end 1 or 2 is detected, and the switching unit 5 is controlled based on this detection operation. Alternatively, the reception output from 2 is selected. Further, a pair of antennas 11 and 12
Are switched by switches 13 and 14, respectively, and distributed to first and second front ends 1 and 2, respectively. The switches 13 and 14 are also switched by the diversity switching unit 15.

FIG. 2 shows the first and second front ends 1.
2 and 2 show a basic configuration. An input signal from the antenna 11 or 12 is tuned by the antenna tuning unit 21, and is amplified by the RF amplifier 23 via the attenuator 22. The output from the RF amplifier 23 is tuned by the tuning section 24 of the RF stage, mixed with the local oscillation frequency from the local oscillator 26 by the frequency mixer 25, and becomes an intermediate frequency signal, which is amplified by the IF amplifier 27 and To the FM detection circuit 3 or 4. The signal taken out of the IF stage is smoothed by an automatic gain control unit (AGC) 28 to generate AGC powers 29a and 29b. The AGC power 29a controls the attenuator 22. The gain of the FET 23 is controlled, and the strong input of the antenna is suppressed by the bypass function of the attenuator 22 and the gain control of the RF amplifier 23.

Here, the difference in reception characteristics between the first front end 1 and the second front end 2 will be described based on the diagram of FIG. In FIG. 3, a indicates the intensity (horizontal axis) of the input signal to the front end 2 when there is a reception input of the desired selected station (reception input of the frequency f0 in FIG. 4) at the second front end 2. , And changes in the intensity of the IF output (vertical axis) from the front end 2. Similarly, FIG. 3B shows a change in the strength of the input signal and the strength of the IF output when there is a reception input of the desired selected station on the first front end 1.

FIG. 3C shows the intensity of the input signal to the front end 2 and the IF output when an interfering wave (interference wave of frequency f3 in FIG. 4) is input to the second front end 2; In the same figure, d in the figure indicates a change in the input signal intensity and the IF output intensity when an interfering wave is input to the first front end 1.

The second front end 2 has excellent reception sensitivity.
The first front end 1 has the receiving sensitivity
That prioritizes the response characteristics to intermodulation interference
It has become. That is, the first front end 1 and the second
Front end 2 and each attenuator 2
2 and the amplification characteristics of the RF amplifier 23
The amplification gain up to the frequency mixer 25 is different.
As shown in FIG. 3, the gain of the second front end 2 and the
Gain difference A is set between the gain of the front end 1 and the gain of the front end 1
Automatic gain control in the first front end 1
Automatic gain control is applied by the control unit 28Input signal strength
However, automatic gain control is not performed in the second front end 2.
KaruruInput signal strengthOnly B thanLowHas become. this
Automatic gain control is appliedInput signal strengthThe difference is
For example, the automatic gain control shown in FIG.
Set by changing the capacitance Ca of the input unit to the control unit 28
it can.

Due to the gain difference A and the difference B at the time when the automatic gain control is performed, the reception sensitivity by the second front end 2 is higher than the reception sensitivity by the first front end 1. Due to this difference in sensitivity, the second front end 2 has priority on the reception sensitivity, and the first front end 1 has priority on the response to intermodulation interference. As shown in FIG. 4, the intermodulation interference wave (f3) caused by the broadcast waves of the two frequencies f1 and f2 is divided into the respective frequencies f1 and f2.
And the interference with their higher harmonic components, the intensity change between the input of this intermodulation interference wave (f3) and the IF output becomes
As shown by c and d in FIG. 3, the desired selected station (f0)
Is three times the slope of the input-IF output curve. Therefore, the IF output based on the intermodulation interference wave (f3) in the first front end 1 is changed to the second front end 2 by the gain difference A and the difference B between the start points of the automatic gain control.
Is very low compared to the IF output from

In this manner, the second front end 2
Is the reception sensitivity priority, and the first front end 1 is the response priority to intermodulation interference. In addition, for example, by providing the input of the frequency mixer 25 with selectivity in the first front end 1 or forming a front end with an element having good linearity, the characteristic of the first front end 1 against intermodulation interference is provided. May be made higher than the characteristic of the intermodulation interference in the second front end 2.

Next, it is assumed that the second stereo demodulation circuit 8 which functions as an output detector for detecting the reception output from the second front end 2 has a low pilot sensitivity. FM
Frequency shift of pilot signal in stereo reception is 7.5
kHz. In the interfering wave (f3) due to the intermodulation, the frequency shift of the pilot signal is doubled or tripled due to interference with a harmonic component. Therefore, the second stereo demodulation circuit 8 functioning as an output detection unit detects that the pilot signal is 7.5 kHz or more, for example, 15 kHz or more, thereby detecting that interference due to intermodulation has occurred. Further, since the first stereo demodulation circuit 7 demodulates a normal stereo signal, the reception of the stereo signal is detected by detecting that the pilot signal is 7.5 kHz or less. .

Next, the receiving operation of the receiving apparatus according to the above embodiment will be described. When the receiving operation is started, the switching unit 5 is controlled by a command from the control unit 9 to give priority to the reception output from any front end. For example, the second
Priority is given to the reception output from the front end 2 and sensitivity-priority reception is performed. However, at this time, the diversity switching unit 15 outputs the reception output from the second front end 2 to F
Monitoring is performed via the M detection circuit 4, the switches 13 and 14 of the antenna input unit are switched as needed, and the antenna 11 or 12 having a high reception strength is selected. Further, the reception output from the first front end 1 and the reception output from the second front end 2 are monitored via the respective FM detection circuits 3 and 4, and a switching unit 5 is provided so as to obtain a detection output with high reception intensity. Is switched, and the reception output from the first front end 1 or the reception output from the second front end 2 is selected.

Here, the reception output from the second front end 2 is always input to the second stereo demodulation circuit 8 via the FM detection circuit 4. When interference due to intermodulation occurs, the pilot signal of the intermodulation interference wave is detected by the stereo demodulation circuit 8 with a frequency shift of, for example, 15 kHz or more. When there is this detection output, the controller 9
The switching unit 5 is switched in response to the command (1), and the received output from the first front end 1 is fixed. In the first front end 1, as shown in FIG. 3, the response to the intermodulation interference is prioritized, so that it is possible to obtain a reception output less affected by the intermodulation interference. However, even when the reception path is fixed to the first front end 1, the reception paths from the antennas 11 and 12 are switched by the diversity switching unit 15 as needed by the switch units 13 and 14.

When the reception output of the pilot signal of the intermodulation interference wave by the stereo demodulation circuit 8 is lost, the reception mode in which the second front end 2 is given priority again, or the reception from the first and second front ends is performed. It returns to the normal mode in which the output is switched at any time.

In the above embodiment, the switch sections 13 and 14 are provided in the antenna input section, and the diversity switch section 1 is provided.
5, the antenna input is selected, but the antenna input may not be switched.

[0023]

[0024]

[0025]

As described above, according to the present invention, the phase of the receiving sensitivity is improved.
Equipped with two different front ends, receiving when normal reception
Enables high-sensitivity reception using a highly sensitive front end
When receiving intermodulation interference,
The use of the
Can be reduced. It also checks whether or not there is intermodulation interference.
Detect based on the frequency shift of the teleo pilot signal
Detection accuracy
Can be higher.

Further, the first front engine having low reception sensitivity
The input signal strength for which automatic gain control is
At the end of the input signal, which is subject to automatic gain control.
Also lower, when switching to the first front end
The intensity of the intermodulation component in the intermediate frequency signal is extremely low.
And minimize the effects of intermodulation interference.
You.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram illustrating a receiving device according to an embodiment of the present invention;

FIG. 2 is a circuit block diagram showing a basic configuration of a front end;

FIG. 3 is a diagram showing reception characteristics of each front end;

FIG. 4 is a diagram illustrating intermodulation interference;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 first front end 2 second front end 3, 4 FM detection circuit 5 switching unit 7 stereo demodulation circuit 8 stereo demodulation circuit as output detection unit 15 diversity switching unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04B 1/10-1/14 H04B 7/00 H04B 7/02-7/12 H04B 15/00-15 / 06 H04L 1/02-1/06

Claims (2)

(57) [Claims] A first intermediate frequency signal is output from a received signal.
A first front end for powering said first front end;
Receiving sensitivity is higher than that of the
A second intermediate frequency signal having a greater intensity than the frequency signal.
Output second front end and intermodulation
Frequency deviation is greater than the frequency deviation during normal reception
The converted stereo pilot signal to the second intermediate frequency.
Intermodulation to detect intermod interference by detecting from the signal
Intermod interference is detected by the tone detection unit and the intermodulation detection unit.
If not, the second intermediate frequency signal is restored in stereo.
When the intermodulation interference is detected
Outputs the first intermediate frequency signal to the stereo demodulation unit.
And a switching means for causing the receiving device to be provided. 2. The first front end and a second flow.
The end is an RF amplifier that amplifies the received signal,
The amplification gain of the RF amplifier is adjusted according to the strength of the frequency signal.
An automatic gain control unit for controlling the first front
Automatic gain control by the automatic gain control unit at the end
The strength of the input signal is at the second front end
Automatic gain control by the automatic gain controller
The receiving device according to claim 1, wherein the setting is lower than the intensity .