JPS6230536B2 - - Google Patents

Description

Detailed Description of the Invention The present invention automatically sweeps the tuning frequency by changing the capacitance value of the variable capacitance element used in the antenna tuning circuit and local oscillation circuit in a receiver, especially in a motor drive or digital control system. This paper relates to an automatic tuning type AM receiver that uses automatic tuning.

Conventionally, this type of receiver generally has a built-in tuning detection circuit that determines whether or not it is in a tuned state.
Depending on the determination level of the tuning circuit, it is determined whether or not to stop sweeping the tuning frequency. In other words,
When the electric field strength of the received radio wave reaches a desired value (hereinafter, this value is referred to as the judgment limit electric field strength), the judgment level of the tuning circuit is inverted from low level to high level (or from high level to low level). ,
This stops the capacitance value change of the variable capacitor and allows the receiving operation to be performed.

Therefore, in a range where the electric field strength is smaller than the decision limit electric field strength, the tuning frequency sweep does not stop and the receiving state does not occur. On the other hand, in a range where the electric field strength is greater than the determination limit electric field strength, the tuning frequency sweep is stopped by the determination output of the tuning detection circuit, and the state is fixed in a receivable state.

In this way, the judgment limit electric field strength is determined by the judgment level and voltage gain settings of the tuning detection circuit, so it is possible to obtain an output with a sufficiently good signal-to-noise ratio (S/N ratio) and to be able to withstand external noise radio waves. However, if the determination limit strength is set to a sufficiently strong electric field strength of, for example, 40 to 50 dB/m, in order to eliminate erroneous operation of the tuning detection circuit, the determination operation of the tuning detection circuit will be hindered. This is because when the above-mentioned received signal with sufficiently high field strength is input, the input signal level of the tuning detection circuit is held almost constant by the action of the automatic gain control circuit (hereinafter referred to as the AGC circuit). Normally, a tuning detection circuit compares a certain reference voltage with an input signal level, and uses the comparison output as a frequency sweep stop signal. Therefore, if variations occur in the value of the reference voltage due to temperature characteristics or the like, variations will also occur in the determination operation for a substantially constant input signal level.

As shown in Figure 1, a conventional method proposed to solve this problem is to forcibly reduce the voltage gain of the receiver using an external switch, thereby preventing the input of a received signal with a strong electric field strength. Also provided is a so-called local distance switching section 12 that prevents the amplified output from reaching the output level determined by the AGC circuit. That is, depending on the resistance value of the variable resistor 14 connected to the local distance switching section 12, the selectivity Q of the antenna tuning section 2 is reduced in the case of FIG.
Even when the electric field strength is 50 dB/m, the input signal level of the tuning detection section 2 is made to change linearly, so that the apparent determination limit electric field strength is increased. As a result, when the signal input from the antenna 1 has a weak electric field strength, the control section 9 applies the signal to the variable capacitance diode of the antenna tuning section 2 and the local oscillation circuit section 5 by, for example, a high level output of the tuning detection section 8. The frequency sweep is continued by changing the DC voltage. On the other hand, in response to a strong electric field strength input, the output of the tuning detection section is inverted to a low level, thereby stopping the change in the voltage applied to the control section 9, and also stopping the frequency sweep to enter the receiving state.

The signal selectively tuned by the antenna tuning section 2 is amplified by the high frequency amplification section 3, and mixed with the oscillation output of the local oscillation circuit section 5 by the mixing section 4 to obtain an intermediate frequency signal. This signal is amplified by the intermediate frequency amplification section 6, detected by the detection section 7, and the detected output is obtained from the output terminal 13. Further, the detection output is input to the signal strength detection section 10 and converted into a DC voltage,
The voltage is input to the AGC circuit 11, which controls the gains of the antenna tuning section 2, high frequency amplification section 3, and intermediate frequency amplification section 6.

As described above, according to the receiver shown in FIG. 1, even if the electric field strength is sufficiently strong, the variable resistor 14 of the local distance switching section 12 allows the tuning detection section 8 to perform the determination operation reliably and accurately.

However, in such a receiver, even if the frequency sweep is stopped by the tuning detection section 8, the voltage gain of the antenna tuning section 2 is
and remains lowered by the variable resistor 14.

Generally, it is known that when multiple amplification stages are directly connected, the S/N ratio of the output signal will be better if the gain of the amplifier in the previous stage is set larger. However, in the case of FIG. 1, the gain of the antenna tuning section remains reduced as described above, and as a result, the S/N ratio of the detected output obtained at the output terminal 13 deteriorates.

In order to avoid this, if the local distance switching section 12 is configured to reduce the gain of the intermediate frequency amplification section 6, the judgment operation of the tuning detection section 8 can be performed reliably and accurately as described above.
Furthermore, deterioration of the S/N ratio of the output signal during reception can also be avoided. However, in such a configuration, when a received signal with a sufficiently strong electric field strength is input, the antenna tuning section 2 and the high frequency amplification section 3 become saturated, and the obtained detected signal becomes highly distorted.

In this way, in order to make the judgment operation of the tuning detection section 2 reliable and accurate, in the conventional receiver, the gain of the antenna tuning section 2 and the high frequency amplification stage 3 is configured to be lowered, so that the S of the detection output obtained is reduced. The /N ratio becomes extremely degraded, and if the gain of the intermediate frequency amplification section 6 is lowered in order to eliminate this, the obtained detection output will have a lot of distortion.

SUMMARY OF THE INVENTION An object of the present invention is to provide a receiver that has a simple configuration and implements means for reliably performing a tuning detection operation while preventing deterioration of the S/N ratio and increase of distortion rate.

The present invention combines a transistor in parallel with a tuning coil of an antenna tuning section, and provides a signal indicating a sweep condition to the transistor, and also provides an automatic gain control signal, thereby controlling the tuning coil of the antenna tuning section. The present invention is characterized in that the transistor performs both gain control in the tuned frequency sweep state and gain control in the sweep stop state.

That is, in the present invention, a signal indicating the sweep state is supplied to the transistor to lower the gain of the antenna tuning section, thereby performing a tuning detection operation without increasing the distortion factor. provides an automatic gain control signal to
This prevents deterioration of the S/N ratio, and since one transistor is shared, the configuration for this purpose is simplified.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a block diagram showing the operating principle of the present invention, and the same functions as those in FIG. 1 are designated by the same numbers and their explanations will be omitted. In FIG. 2, the electric field strength of the received signal is determined by converting the signal of the local distance section 12 to the output signal of the tuning detection section 8, that is, the apparent judgment limit electric field strength due to the local distance section 12 and the variable resistance value 14. It is input to the antenna tuning section 2 via a gate circuit section 15 that operates based on a signal for stopping the frequency sweep when the frequency is reached.

Therefore, when synchronization is not achieved and the electric field strength is weak, the gate circuit section 15 opens its gate in response to a high level signal from the synchronization detection section 8, and the judgment limit electric field strength is determined by the local distance section 12 and the variable resistor. It is determined by the gain of the amplifier 14 and the amplification stage of the receiving section and the judgment level of the tuning detection section 8. Therefore, even if the electric field strength is strong, by lowering the gain of the antenna tuning section 2, the determination operation of the tuning detection section 8 can be performed reliably and accurately.

On the other hand, when the input electric field strength becomes larger than the apparent judgment limit strength, the gate of the gate circuit section 15 is closed by the low level output signal which becomes the frequency sweep stop signal of the tuning detection section 8, and the gain of the antenna tuning section 2 is changed by the variable resistance. It is controlled by the AGC circuit section 11 regardless of the resistance value of the device 14. As a result, the gain of the antenna tuning section 2 becomes large, and the V/N ratio of the obtained detection output also becomes good.

Based on the above-mentioned operating principle, the present invention provides means for realizing gain control during tuning frequency sweep of the antenna tuning section 2 and gain control in the tuned state with a simple configuration. Shown in Figure 3.
Note that, in FIG. 3, the tuning detection section 8, local distance section 12, gate circuit section 15, and antenna tuning section 2 are shown for the sake of simplification of explanation.

That is, the output of the intermediate frequency amplifying section 6 inputted from the terminal 30 is rectified by an AM detector consisting of a transistor Q ₁ , a resistor R ₁ and a capacitor C ₁ via a ceramic filter 31, and is then sent to one input terminal of the differential amplifier. is applied to the base of transistor _Q2 . The base of the transistor Q ₃ , which is the other input terminal, is connected to the voltage drop generated in the diode D ₂ of the bias circuit consisting of the diodes D ₁ and D ₂ and the resistor R ₂ , which is divided by the resistors R ₃ and R ₄ . is supplied as a reference voltage. At this time, the resistance R ₃ and
Depending on the setting of R ₄ , the base potential of transistor Q ₃ is
It is set higher than the base potential of transistor _Q2 by 0.1-0.2V. Thus, at low field strengths, transistors Q ₂ and Q ₃ are in a cut-off and conduction state, respectively. Note that the diode D ₃ and the transistor Q ₄ are the load of the differential amplifier, and the resistor R ₅ constitutes a current source.

Transistor Q ₅ due to the interruption of transistor Q ₂
A high level potential is applied to the bases of the transistors Q ₅ and Q 6 , thereby making the transistors Q 5 and Q ₆ conductive, and their collector potentials become low level. If it is desired to comply with the description of FIGS. 1 and 2, an inverting amplifier may be further connected to each collector output, or transistors Q ₅ and Q ₆ may be removed. moreover,
The subsequent circuit operation may also be configured to be reversed.

The collector of transistor Q ₅ is gate circuit section 1
As a signal to 5, the collector of transistor Q ₆ is used as a signal to control 9 via terminal 33. Due to the conduction of the transistor _Q5 in this weak electric field, the current of the constant current source 32 is drawn in, so that the base of the transistor _Q7 via the diodes _D4 and _D5 becomes low level. Therefore, transistor Q ₇ is cut off, which means that gate circuit 1
5 is opened, and the gain of the antenna tuning section 2 is lowered by the local distance switching section 12 and the variable resistor 14.

That is, a bias voltage is generated in the diodes D ₆ and D ₇ due to the current from the constant current source 34 due to the cutoff of the transistor Q ₇ , which causes the transistor Q 7 to be cut off.
Q ₈ is conductive. A constant current source 34 supplies a predetermined current to the base of the transistor Q ₈ , and the collector current can be arbitrarily set by the resistance value of the variable resistor 14 connected to the terminal 35 . Due to the voltage drop across resistor R ₆ and diode D ₈ due to the collector current of transistor Q 8, transistor _{Q 9} becomes conductive.
Q ₁₀ and Q ₁₂ are conductive. The collector of transistor Q ₁₂ is connected to terminal 36 and is further connected to capacitor C ₂
It is connected to the antenna tuning section 2 via.

The antenna tuning unit 2 has a terminal 41 applied with a signal voltage for tuning frequency sweep from the control unit 9,
It is composed of a variable capacitance diode 39 whose capacitance value changes accordingly, and a tuning coil 40, and the collector of the transistor _Q12 is connected to the variable capacitance diode 3.
9 and the coil 40.

Therefore, the current of the transistor _Q8 determined by the resistance value of the variable resistor 14 causes the transistor
_Q12 's collector-emitter conduction impedance changes. As a result, the impedance at the connection point between the coil 40 and the variable capacitance diode 39 changes, thereby reducing the selectivity Q of the antenna tuning section 2 and ensuring determination operation for stronger electric field strengths. It is assumed to be accurate.

Note that the other end of the tuning coil 40 is connected to a terminal 42 which is an input to the high frequency amplification section ₃ via a capacitor C3. Further, a terminal 43 is connected to the base of the transistor _Q10 , and the AGC
AGC voltage by circuit 11 is supplied.

Next, when the electric field strength of the received signal becomes 40 to 50 dB/m or more and the emitter potential of transistor Q ₁ , that is, the base potential of transistor Q ₂ becomes larger than the input difference of the differential amplifier, about 0.2 V, transistor Q ₂ conducts. This allows the transistor
Q ₅ and Q ₆ are blocked. By blocking transistor Q ₆ , the signal level available at terminal 33 is reversed,
At that point, the voltage change in the control section 9 stops and the tuning frequency sweep stops.

At the same time, the current of the constant current source 32 is supplied to the base of the transistor Q 7 by cutting off the transistor Q ₅ , and _{the transistor Q 7 becomes} conductive. When transistor Q ₇ becomes conductive, it draws current from constant current source 34, so transistor Q ₈ is cut off. Therefore, transistor _Q9 is also cut off, and transistor
Current supply from the variable resistor 14 to Q ₁₀ and Q ₁₂ is eliminated. Therefore, the antenna tuner 2 is connected to the terminal 4.
It operates with a voltage gain determined by the AGC voltage input from 3, and there is no problem of deterioration of the S/N ratio of the obtained detection output.

As described above, according to the present invention, with a simple configuration, tuning detection judgment can be performed reliably and accurately under strong electric field strength, and the S/N ratio of the detection output is sufficiently good as well as the distortion rate is also good. becomes. Furthermore, since the gain when out-of-tuning is small, it is possible to reduce the unpleasant noise that occurs when receiving in a place where there is no broadcast radio wave.

It goes without saying that the present invention is not limited to the above embodiments. That is, the state of change in the output signal level of the tuning detection section 8 can be set arbitrarily, and the operating state of the gate circuit section 15 can be changed accordingly. or,
In the specific circuit configuration shown in FIG. 3, an inverting amplifier or circuit element may be inserted as appropriate. Furthermore, the control of the variable capacitance diode by the control section 9 may also be applied to the high frequency amplification section 3, and the variable resistor 14 may also be a fixed resistor with an appropriate value in advance.
Furthermore, the input to the tuning detection section 8 may be taken from the detection section 7, and the input to the signal strength detection section 10 may also be taken from the intermediate frequency amplification section 6.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional automatic tuning type AM receiver, FIG. 2 is a block diagram showing the operating principle of the present invention, and FIG. 3 is a circuit diagram showing an embodiment of the present invention. 1...Antenna, 2...Antenna tuning section, 3...
... High frequency amplification section, 4 ... Mixing section, 5 ... Local oscillation circuit section, 6 ... Intermediate frequency amplification section, 7 ... Detection section,
8... Tuning detection section, 9... Control section, 10... Signal strength detection section, 11... AGC circuit section, 12... Local distance switching section, 13... Output terminal, 14... Variable resistor , 15...gate circuit section, _Q1 - _Q12 ...transistor, _R1 - _R6 ...resistor, _C1 - _C3 ...capacitor, 31...ceramic filter, 39...variable capacitance diode, 40
...tuning coil.

Claims (1)

[Claims] 1 In response to a signal indicating that the tuning frequency is in the sweep state, the gain of the antenna tuning section is lowered, the tuning frequency is swept in this state, and when the signal level of the tuning frequency reaches a predetermined value, the tuning frequency is changed. In the receiver, the sweep is stopped, and the generation of the signal indicating the sweep state is stopped, and the gain of the antenna tuning section is set to a state determined by the automatic gain control signal in the tuning state. The antenna tuning section has a tuning coil and a transistor coupled substantially in parallel to the coil, and provides the transistor with a signal indicating the sweep condition and provides the automatic gain control signal; Accordingly, the receiver is characterized in that the transistor is used in common to perform gain control in the tuned frequency sweep state of the antenna tuning section and gain control in the sweep stop state.