JPH0227631Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an FM/AM electronically tuned receiver that uses a simple circuit configuration to switch between FM and AM _DX / _LO during automatic tuning. be.

In FM/AM electronically tuned receivers that incorporate a PLL frequency synthesizer function and are capable of automatic tuning,
A variable capacitance diode is used as a tuning circuit element in the FM/AM tuner circuit, and by applying a tuning control voltage corresponding to the receiving frequency of the desired broadcasting station, the desired broadcasting station is automatically selected. It is composed of The FM/AM electronically tuned receiver is also equipped with an AGC circuit, and is configured to adjust the reception sensitivity of the receiver according to the antenna input electric field strength.

When performing automatic tuning operation in such an FM/AM electronically tuned receiver, the received signal is extracted from an appropriate circuit stage of the receiver, such as an intermediate frequency amplification stage, according to the antenna input electric field, and then added to a controller such as a microcomputer. , set the automatic stop sensitivity level on the controller in advance, such as the _DX stop sensitivity level, and when the controller scans within a certain range of frequency bands, it will automatically select a station when it seeks a signal above the set level. It's starting to stop working.

By the way, the electric field strength input from the antenna fluctuates with time, and there is a considerable difference between day and night, and generally, at night, due to fading, beats, spurious, etc., it is difficult to receive more broadcast waves than during the day. becomes possible. For this reason, at night, the above setting level is set higher, for example, as the L _O stop sensitivity level, and the configuration is configured so that only signals with a higher input level than during the day can be received, so that only stronger received signals can be tuned. do. Note that the automatic channel selection operation is generally possible only when the antenna input level is medium or weak in the electric field, and becomes inoperable in the high electric field due to the saturation characteristics of the high frequency amplification circuit and the like.

The automatic stop sensitivity level switching from _DX to _LO is performed by controlling the gains of the FM and AM tuner circuits in accordance with each switching signal.

Figure 1 shows the tuner section of a conventional FM/AM electronic tuning receiver, where A is the FM tuner circuit, B is the AM tuner circuit, _Q1 to _Q5 are transistors, _D1 to _D6 are diodes, R _A , R _B , R _C , R ₁ ,
R ₂ is a resistance, C ₁ to C ₃ , C _A , C _B , C _T are capacitors,
L ₁ to L ₃ , L _X , and L _O are inductors, and _VR is a volume. Also, T ₁ is the antenna input terminal, T ₂ is _D
L _O switching signal input terminal, V _T is tuning control voltage, V _CC is power supply voltage, A ₁ is AM AGC amplifier, S ₁ and S ₂
indicate the downstream circuits below the mixer stage for FM and AM, respectively.

Transistor Q ₁ consists of a dual gate FET and operates as a high frequency amplifier circuit for FM. The FM input signal from the antenna is applied to the first gate G ₁ , and the AGC voltage is applied to the second gate G ₂ to adjust the gain. Control. Transistor Q ₂ consists of a FET
It operates as an AM high-frequency amplifier circuit, and an AM input signal is applied to the gate G. Transistor Q ₃ ~
_Q5 consists of an NPN type transistor, and both perform switching operations. Of these, Q ₃ is AGC for AM
It acts as a switching transistor for Q ₄ ,
_Q5 is a D _X /L _O switching transistor that performs switching operation under the control of each FM and AMD _X /L _O switching signal. Diodes D ₁ to D ₃ consist of variable capacitance diodes, and diode D ₁ constitutes an FM antenna tuning circuit together with inductor L ₁ .
Diode D ₂ constitutes an FM high frequency tuning circuit together with inductor L ₃ , and diode D ₃ constitutes an AM high frequency tuning circuit together with capacitor _CT and inductor L _X .

Diodes D ₄ and D ₅ are for AMAGC voltage rectification, resistors R ₁ and R ₂ and capacitors C ₁ and C ₂ constitute a smoothing circuit, and the DC voltage obtained from these is connected to the above switching circuit via diode D _6. transistor Q ₃
added to.

In the above configuration, when performing the automatic tuning operation of the receiver, if the controller is operated to first operate the FM tuner circuit and set the automatic stop sensitivity level to the L _O position, then the terminal T ₂ is connected to the H signal from the controller. A level signal is added. This turns on transistor _Q4 , and the second gate _G2 of _FETQ1 is grounded via resistor R _A.
Until then, this G ₂ is transmitted from the mixer stage of the subsequent circuit S ₁ , etc.
The AGC voltage (gate bias voltage) that had been applied to the gate is now applied only as it is divided by this resistor _RA . As a result, the AGC voltage decreases, so the gain of FETQ ₁ decreases, and the FM input signal applied to the first gate G ₁ becomes −
It is controlled to be attenuated by α (dB). Therefore, such attenuation of the gain for the FM input signal during L _O mode apparently corresponds to an increase in the automatic stop sensitivity level. In other words, even if the auto-stop sensitivity level is set _{to D}
As a result of switching to AGC and attenuating the gain, effectively only signals stronger than the L _O automatic stop sensitivity level are received.

At this time, transistor _Q5 is also turned on, but the base resistance R _C is selected to be high (20 to 30 kΩ), so
It has no effect on the AM side at all.

Next, if we operate the AM tuner circuit and operate the controller to set the automatic stop sensitivity level in the L _O position, an H level signal is applied from the controller to terminal _T2 . This turns on the transistor _Q5 , so that the signal line at point _XB of the AM high frequency tuning circuit is grounded via the capacitor _C3 , the volume _VR , and C-E of _Q5 , and the signal voltage is attenuated. As a result, the gain of FETQ ₂ is reduced, so that the automatic stop sensitivity level appears to be increased as in the case of the FM tuner circuit described above. At this time, transistor _Q4 is also turned on, but since the base resistance R _B is selected to be high (20 to 30 kΩ), it does not affect the FM side at all.

During this automatic tuning operation, at weak electric field levels,
Since the voltage level obtained from the AM AGC amplifier _A1 and the smoothing circuit connected thereto is small, the transistor _Q3 is turned off. On the other hand, at high electric field levels, the voltage level becomes high and transistor Q ₃ turns on, grounding and attenuating the AM input signal, so the gain of FET Q ₂ is significantly reduced. Particularly in the case of AM, a large antenna input is applied at high electric field levels, so this transistor _Q3 is specifically provided to handle the large input.

By the way, in the conventional FM/AM electronically tuned receiver as described above, the FM and AM tuner circuits are provided with separate _DX / _LO switching transistors, and in addition to these, resistors and capacitors are required. As a result, the number of circuit components increases, resulting in an unavoidable increase in costs. For this reason, an attempt was made to make the transistors Q ₄ and Q ₅ common in FIG. 1, but there was a problem that the FM and AM tuner circuits inevitably influenced each other due to impedance.

This invention was developed in response to the above problems, and it uses a common D _X /L _O switching transistor for FM and AM, and also
FM/
The purpose is to provide an AM electronically tuned receiver.

Embodiments of the present invention will be described below with reference to the drawings.

FIG _. 3 is a circuit diagram showing an FM/AM electronic tuning receiver according to an embodiment of the present invention. _The same parts as in _FIG . _Q7 is an NPN transistor
Controls the drain voltage of FETQ ₂ , which functions as a high-frequency amplifier circuit for AM. D ₇ and D ₈ are diodes R _d ,
R _E , R _k , R _R , R _S , R _X , and R _y are resistors, C _Y is a capacitor, and L _S is an inductor.

The base of the transistor Q ₆ above is the diode D ₇
and D _X / L _O switching signal input terminal via resistor R _d
T ₂ and its collector output point Y ₀ is connected to the resistor _R
is connected to the drain of the transistor Q ₂ of the AM tuner circuit through the resistor R _k and the transistor of the FM tuner circuit through the inductor L _S
Connected to the second gate _G2 of _Q1 . In addition, the drain output point _Y1 of the transistor _Q2 above is a transistor
Connected to the emitter of Q ₇ . Further, resistors R _S and R _R are connected to the second gate G ₂ of the transistor Q ₁ .

On the other hand, the AGC voltage obtained from, for example, the mixer stage of the downstream circuit _S1 of the FM tuner circuit is connected to the base of the transistor _Q6 via the connection point P, the resistor _RE , and the diode _D8 .

Note that this AGC circuit is of the type that operates for the first time and generates the AGC voltage V _A when the input level exceeds a predetermined level V _X as shown in Figure 4. It is set to operate only when the input level becomes high and not to operate in weak or medium electric fields.

When the antenna input level is weak and the electric field is medium, the transistor Q ₁ supplies its second gate G ₂ with the power supply voltage V _CC divided by the resistors R _R and R _S , and the voltage dropped by the resistor R _S as the bias voltage. It is working because it has been added.

Considering the automatic tuning operation when receiving FM, an L level is applied to the terminal T ₂ during D _X , so the transistor Q ₆ is turned off. Also at this time, the transistor Q ₂ ,
_Q7 is also turned off, and the drain output point _Y1 is kept at high impedance due to the presence of the resistor _Rk , inductor _Ls, etc., so there is no mutual influence between the FM side and the AM side.

Next, since the H level is applied to the terminal T ₂ during _LO , the transistor Q ₆ is turned on, and the second gate G ₂ of the transistor Q ₁ is connected to the inductor L _S , the resistors R _k , _YO , and the C-E of the transistor Q ₆ . grounded via. As a result, the bias voltage for the second gate _G2 decreases, so the gain of the transistor _Q1 decreases, and the automatic stop sensitivity level apparently increases.

Next _, during _AM reception _{and D} .

Next, since an H level is applied to the terminal T ₂ during _LO , the transistor Q ₆ is turned on, and the drain output point Y ₁ is grounded through the resistors R _X , Y _O and C-E of the transistor Q ₆ . As a result, the signal voltage at the output point _Y1 of transistor _Q2 is attenuated, so the above FM
As in the case of , the automatic stop sensitivity level increases.

Therefore, transistor Q ₆ is FM, AM each _D
Can be shared as a L _O switching transistor.

Furthermore, when the antenna input is in a high electric field, the AM high frequency signal picked up by the collector output point _Y2 of the transistor _Q7 is transferred to the capacitor _Cy , the resistor
It is added to the AGC amplifier A ₁ via _Ry , and after being sufficiently amplified as an AGC signal, it is rectified by diodes D ₄ and D ₅ , and further consists of capacitors C ₁ and C ₂ and resistors R ₁ and R _2. After being made into a DC voltage by a smoothing circuit, it is applied to the base of transistor _Q6 via diode _D6 . This turns on transistor _Q6 and attenuates the AM input signal to _FETQ2 , which functions as an AM high-frequency amplifier circuit, so that the gain of _FETQ2 is reduced.

On the other hand, in the case of FM high-frequency signals, as is clear from Figure 4, when the antenna input becomes a high electric field, an AGC voltage is generated at the connection point P and is applied to the base of _{transistor Q6 via} diode D8. ₆ turns on. Yotsute transistor Q ₁
The gain of is reduced and AGC operation is performed.

Therefore, both FM and AM can be adequately supported even in high electric fields where automatic channel selection is impossible.

Also, by providing diodes D ₆ , D ₇ , and D ₈ , AM AGC signal, D _X /L _O switching signal and
Mutual influence of each FM AGC signal can be avoided.

As stated above, according to the present invention,
Since _{the D} be able to. Moreover, the purpose can be achieved without mutual influence between FM and AM.

[Brief explanation of the drawing]

1 and 3 are circuit diagrams showing conventional and embodiments of the present invention, and FIGS. 2 and 4 are graphs for explaining the present invention. A...FM tuner circuit, B...AM tuner circuit,
_Q1 to _Q7 ...transistor, _D1 to _D7 ...diode,
P... Connection point, T ₁ ... Antenna input terminal, T ₂ ... D _X /
L _O switching signal input terminal.

Claims (1)

[Claims _{for Utility Model Registration] 1. A switching element for DX/LO switching to which FM and AM DX / LO switching} signals are applied, and a high-frequency amplifier circuit for FM connected to the output side of this switching element, respectively. and an AM high-frequency amplifier circuit connected between the input side of the switching element and the output side of the FM high-frequency amplifier circuit.
AGC signal generation circuit for FM, and AM circuit connected between the input side of the above switching element and the above high frequency amplifier circuit for AM.
and an AGC signal generation circuit, and when the antenna input level is low during automatic channel selection operation, _{the D}
The switching element controls the FM high-frequency amplification circuit or the AM high-frequency amplification circuit, so that the antenna input level in high conditions
By AGC signal for FM or AGC signal for AM
An FM/AM electronic tuning receiver, characterized in that the switching element is configured to control the FM high frequency amplification circuit or the AM high frequency amplification circuit so that an AGC operation is performed. 2 The above AGC signal generation circuit for FM and for AM
2. The FM/AM electronic tuning receiver according to claim 1, wherein the AGC signal generating circuits are each connected to the _DX / _LO switching switching element via a diode.