JPS6138281Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention aims to improve the characteristics of low receiving frequencies in an electronically tuned receiver that uses a variable resistor to supply a bias voltage to the voltage variable capacitance element of the tuning circuit. This is the purpose.

Prior to explaining the present invention, a conventional preset electronic tuning receiver using a voltage variable capacitance element such as a voltage variable capacitance diode and a variable resistor for supplying a bias voltage to the voltage variable capacitance diode will be described in FIG. This will be explained with reference to the conventional example shown in .

In Figure 1, 1 is the preset setting circuit for the first channel _CH1 to the nth channel CHn, Eb is the bias power supply for the voltage variable capacitance diode, and VR ₁ to _{VR o} are the fine adjustment variable resistors for presetting each channel. , R ₁ is a resistance for supplying the minimum operating voltage Vb to the voltage variable capacitance diode, S ₁ ~ _{S o}
are interlocking push switches for changing channels; contacts b and c are connected only to the switch corresponding to the pushed channel, and contacts a and b are connected to all other switches.

ANT is an antenna, 2 is an antenna circuit, _D1 is a voltage variable capacitance diode that constitutes a tuning circuit of the antenna circuit, 3 is a high frequency amplification circuit, and _D2 is a voltage variable capacitance diode that constitutes a tuning circuit of the high frequency amplification circuit. be. 4 is a mixing circuit, 5 is a local oscillation circuit, ^D3 is a voltage variable capacitance diode that constitutes the oscillation tuning circuit of the local oscillation circuit, C is a high-pass capacitor provided between the bias voltage transmission line L and earth 10, R _B , R _B and R _B are alternating current blocking resistors connected between the bias voltage transmission line L and each of the voltage variable capacitance diodes D ₁ , D ₂ , and D ₃ . 6 is an intermediate frequency amplification circuit, and 7 is a detection circuit.

In the circuit shown in Figure 1, a variable resistor is used to finely adjust the bias voltage of the voltage variable capacitance diodes D ₁ , D ₂ , and D _3.
By storing VR ₁ to _{VR o} and electrically switching these, a frequency set in advance for each channel is received.

As shown in Figure 2, the fine adjustment variable resistors VR ₁ to VR _o are based on the structure of a conventional slide volume, and the resistance value is adjusted by rotating the knob 8. In order to indicate the amount of movement of a slider (not shown), a pointer 9 is directly connected to the slider of the variable resistor. In addition, the linear B curve is adopted for the variable resistor's change characteristics, which is advantageous for ease of manufacture, variation in resistance change characteristics, and environmental change characteristics. Discontinuities sometimes occurred at the beginning and end. The discontinuous characteristic of this variable resistor is
This results in discontinuous characteristics of the bias voltage applied to the voltage variable capacitance diode, that is, a phenomenon in which the receiving frequency jumps.
In particular, since the voltage-capacitance change characteristic of a voltage variable capacitance diode is large when the bias voltage is low, it becomes a time problem in setting a frequency that covers the low range of the receiving frequency. For example, in the case of an FM band receiver for Europe, when the resistance change is △Rl = △Rh = △1/60RO for the receiving frequency setting of 88.5 to 108.0MHz, [however, △Rl and △Rh are variable resistors respectively. The resistance values corresponding to the discontinuous parts at the beginning and end of rotation, RO is the maximum value of the variable resistor. ] Frequency jump in low range is approximately 1M
Hz, the frequency jump in the high range is approximately 150KHz, which indicates that there is a problem with the frequency settings that cover the low range in particular.

Figure 4 shows the reception frequency characteristics when the circuit of Figure 1 is used, and each variable resistor VR ₁ ,
This shows that discontinuities occur in △Fl ₁ in the first channel, △Fl ₂ in the second channel, and △Fl ₃ in the third channel due to variations in VR ₂ and VR ₃ . Since the discontinuity is very small, it does not pose a particular problem.

In this way, in conventional preset electronic tuning receivers,
Frequency skipping phenomenon sometimes occurred near the lowest receiving frequency and near the highest receiving frequency that can be set with the variable resistor due to discontinuous portions of the variable resistor. In the case of commonly used linear variable type (JIS B characteristics) variable resistors, the range of frequency jumps is wide, especially near the lowest receiving frequency, so the nominal lowest receiving frequency and the actual lowest receiving frequency of the set are different. It was necessary to make a very large difference from the frequency.

However, in Europe, there is a police radio band just below the commercial FM band, and the minimum reception frequency of the FM band is strictly regulated by law.
The conventional circuit system shown in the figure was not able to cope with this problem.

In view of this point, the present invention is designed to electrically improve the frequency jump caused by the discontinuous portion of the variable resistor.One embodiment of the present invention will be described below with reference to Figs. 5 and 6. .

FIG. 5 is a circuit diagram of the main parts of the electronic tuning receiver of the present invention. Figure 5 shows each variable resistor VR ₁ for preset setting in the preset setting circuit 1'.
~ In parallel with VR _o , a fixed resistor R ₂ and a semi-fixed resistor for bias voltage adjustment covering the low reception frequency
R ₃ are connected in series, and the slider 11 of the semi-fixed resistor R ₃
and the bias voltage transmission line L, and between the cathode of the first backflow prevention diode and the contact C of _each channel switching button switch _S1 to _S0 . A second backflow prevention diode _D5 is connected to the terminal. A preliminary bias voltage is applied to the voltage variable capacitance diodes D ₁ , D ₂ , and D ₃ in addition to the bias voltages from the variable resistors VR ₁ to _{VR o} .
The rest of the configuration is the same as the circuit shown in FIG.

In the electronically tuned receiver configured in this way,
The voltage of the discontinuous part near the lowest value of the preset variable resistor VR ₁ to _{VR o} is △V _R , and the semi-fixed resistor R ₃
The voltage regulated by △Vb, diode D ₄
If the voltage between the terminals of is Vd, △Vb−Vd＞△V
By setting the fixed resistor R ₂ and semi-fixed resistor R ₃ so that _R , it is possible to eliminate frequency jumps at low reception frequencies. That is, the variable resistor VR ₁ ~
The bias voltage from VR _o is connected to resistor R ₂ and semi-fixed resistor
When the voltage applied to the voltage variable capacitance diode is lower than the voltage applied to the voltage variable capacitance diode set by the preliminary bias setting means consisting of R ₃ , the reverse current prevention diode D ₅
is cut off because it is in a reverse bias state, and when the bias voltage becomes higher than the applied voltage (preliminary bias voltage), the reverse current prevention diode _D5 is forward biased and turned on, and the bias voltage from the variable resistor is reduced. The voltage is now applied to the variable capacitance diode. At this time, the reverse current prevention diode _D4 becomes reverse biased and is cut off, so that the supply of the preliminary bias voltage is blocked.

FIG. 6 is a diagram showing reception frequency characteristics when the circuit of FIG. 5 is used.

In addition, in order to improve the frequency jump caused by discontinuous parts of the variable resistors, the variable range of each preset variable resistor is mechanically limited with screws, etc., so that each variable resistor is not used in discontinuous parts. However, this method has the disadvantage that adjustment is required for each variable resistor, requiring many adjustment points and requiring a large amount of space.

On the other hand, if the frequency jump is electrically improved by the discontinuous portion of the variable resistor as in the embodiment shown in Fig. 5, only the semi-fixed resistor _R3 is required to improve the frequency jump. All you have to do is adjust it.
There are few adjustment points and it is easy to adjust. Moreover, it does not take up much space and is inexpensive. There are advantages such as

As described above, the present invention provides an electronic tuning receiver equipped with a variable resistor that supplies a bias voltage for setting a capacitance value to a voltage variable capacitance element of a tuning circuit. preliminary bias setting means for setting different preliminary bias voltages, and applying a preliminary bias voltage from the preliminary bias setting means to the voltage variable capacitance element when the bias voltage from the variable resistor is below a predetermined level; means for applying the bias voltage from the variable resistor to the voltage variable capacitance element when the variable resistor is at a predetermined level or higher, the frequency jump caused by the discontinuous portion of the variable resistor can be improved with a simple configuration. You can.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of the main parts of a conventional electronic tuning receiver, Figure 2 is a perspective view showing the structure of a variable resistor for presetting used in an electronic tuning receiver, and Figure 3 is a variable resistor for presetting. Fig. 4 is a diagram showing the reception frequency characteristics when the circuit shown in Fig. 1 is used, and Fig. 5 shows the main points of the electronically tuned receiver according to the present invention. Part circuit diagram, 6th
The figure is a receiving frequency characteristic diagram when the circuit of FIG. 5 is used. 2...Antenna circuit, 3...High frequency amplifier circuit, 5...Local oscillation circuit, _D1 , _D2 , _D3 ...Voltage variable capacitance diode, _VR1 to VR _o ...Variable resistor, _R2 ... ... Fixed resistance, R ₃ ... Semi-fixed resistance, D ₄ ,
D ₅ ... Diode for backflow prevention.

Claims (1)

[Claims for Utility Model Registration] (1) In an electronic tuning receiver equipped with a variable resistor that supplies a bias voltage for setting a capacitance value to a voltage variable capacitance element of a tuning circuit, preliminary bias setting means for setting a preliminary bias voltage different from the bias voltage;
When the bias voltage from the variable resistor is below a predetermined level, a pre-bias voltage from the pre-bias setting means is applied to the voltage variable capacitance element, and when the bias voltage is above a predetermined level, the pre-bias voltage from the variable resistor is applied. and means for applying a bias voltage of 1 to the voltage variable capacitance element. (2) The electronic tuning receiver according to claim 1, wherein the voltage variable capacitance element is a voltage variable capacitance diode. (3) The electronic tuning receiver according to claim 1, wherein the variable resistor is a variable resistor for presetting. (4) The preliminary bias setting means is composed of a series circuit of a fixed resistor and a semi-fixed resistor connected in parallel to a variable resistor, and the set voltage can be adjusted by the semi-fixed resistor. An electronic tuning receiver according to claim 1, characterized in that it is a utility model.