JPH0145248B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a channel selection device that limits the receivable frequency range in a television receiver.

(Technical background) In general, television receivers are designed in advance to anticipate that the upper or lower limit of receivable frequencies will change significantly due to errors in parts used in the channel selection device, changes over time, changes in temperature, etc. The receivable frequency band (hereinafter referred to as "sweep range") is designed to be sufficiently wider than the actual broadcast frequency band (hereinafter referred to as "stationed range") with the sole focus of ensuring that television broadcasts can be received reliably.

A so-called "electronic tuning tuner" using a variable capacitance diode as a tuning element in the tuner section has conventionally been equipped with a tuning device as shown in FIG. The tuning section 4 includes a plurality of variable resistors 6 that divide a reference voltage Vz supplied from a power supply 3 equipped with a constant voltage diode 31 to form a tuning voltage for each reception channel, and the output terminal of each variable resistor are connected to each other via switching diodes 51, and the connection point is connected to the tuning voltage input terminal 18 of the tuner 1 via a transistor 71 for temperature compensation.

In the above channel selection device, the tuning voltage Vt can be adjusted, for example, by a sweep operation in which one or more variable resistors 6 are operated over the entire variable range.
It fluctuates in the range of 0.2V to 33±3V, and is designed so that the upper limit of the stationed range can be received when the tuning voltage Vt is, for example, 24V, and the lower limit can be received when it is several volts.

In Figure 6, the horizontal axis shows the tuning voltage Vt, the two vertical axes on the left show the VHF high band and VHF low band frequencies, the right vertical axis shows the UHF band frequency, and each vertical axis shows each band. VHF high band, VHF low band, and
This is a graph showing an example of the reception characteristics of a tuner in the UHF band. Here, the VHF high band station range is E5 to E12 channels,
The VHF low band coverage is E2 to E4 channels, and the UHF band coverage is E21 to E60 channels.

When one or more variable resistors 6 for presetting the tuning frequency shown in FIG. 7 are slid from one end to the other to perform a sweep operation over the entire range, the variable range of the tuning voltage is Even if the contact resistance is taken into account, it will be in a wide range of about 0.2 to 30V as mentioned above. Therefore, when the tuning voltage is changed to the upper and lower ends of the voltage range, an extra sweep operation is performed as described below.

That is, as is clear from the reception characteristics shown in Figure 6, in the VHF low band, the tuning voltage corresponding to the lower limit channel E2 of the station range is approximately 2.5V, and the tuning voltage corresponding to the upper limit channel E4 is approximately 10V. , the sweep operation goes beyond this region from 0.2V
Since it is carried out in the 30V range, there is a channel change equivalent to a change from 0.2V to 2.5V (from the reception frequency approximately 8MHz lower than the E2 channel to the E2 channel), and a channel change equivalent to a change from approximately 10V to 30V (from the receiving frequency approximately 8MHz lower than the E2 channel). (Equivalent to approximately 1.5 channels from E4 channel to slightly beyond E5 channel)
is an extra sweep operation.

Similarly, in the VHF high band, the tuning voltage corresponding to the lower limit channel E5 of the stationed range is approximately 4.5V,
The tuning voltage corresponding to upper limit channel E12 is approximately 18V
However, the sweep operation goes beyond this area.
Since it is carried out in the range of 0.2V to 30V, from 0.2V to
The channel change corresponding to a change of 4.5V (corresponding to several channels) and the channel change corresponding to a change from approximately 18V to 30V (corresponding to approximately 2 channels upward from the E12 channel) are extra sweep operations. becomes.

Furthermore, in the UHF band, the tuning voltage corresponding to the lower limit channel E21 of the station range is approximately 3V, and the tuning voltage corresponding to the upper limit channel E60 is approximately 19V.
Since the sweep operation is performed in the range from 0.2V to 30V beyond this region, the channel change corresponding to a change from 0.2V to 3V (from the receiving frequency approximately 10 channels lower than E21 to E21) and approximately 19V
The channel change corresponding to the change from to 30V (corresponding to approximately 13 channels upward from the E60 channel) is an extra sweep operation.

On the other hand, as the demand for radio waves as a means of communication increases, in order to make effective use of the available frequency bands, in recent years, frequencies have been allocated for private and public communications up to the very vicinity of the standard television broadcasting frequency band. As a result, it has become possible for ordinary television equipment to receive some private communications without any modification, and the question of how to maintain the confidentiality of communications has become a problem.

In order to deal with the above-mentioned problems, there is a movement in various countries to legally limit the reception range of television receivers to only commercial television broadcasts.

For example, the FTZ standard in West Germany or the DOC standard in Canada both strictly regulate the upper and lower limits of the sweep range in television receivers. Taking the FTZ standard as an example, the 6th standard
The UHF band shown in the figure has an upper limit of 878MHz, and the VHF low band has a lower limit of 7MHz lower than the E2 channel.

A simple method to satisfy the above standards is to match the lower limit frequency of each band to the lowest value Vl (for example, 0.5V) of the tuning voltage variable range, and match the upper limit frequency at the highest value of the variable range (30V, for example). It is conceivable to adjust the tuning frequency of each tuner so as to do so. However, since the variable range of the tuning voltage Vt varies depending on the tuning section 4, even if the tuning frequency is adjusted by the tuner alone, a shift in the tuning frequency will occur due to the variation in the tuning voltage. . Therefore, in this case, it is necessary to adjust the receivable range after incorporating the tuner into the receiver, which is extremely troublesome in terms of production. Further, when the tuning voltage is around 0.5V, which is the lower limit of the variable range of the tuning voltage Vt, there are many problems such as the characteristics of the tuner deteriorate and it cannot be put to practical use.

(Summary of the Invention) The present invention utilizes a transistor 71 which has conventionally been interposed between a tuning voltage output terminal and a tuning voltage input terminal of a tuner for temperature compensation, and connects the collector terminal of the transistor 71 to By connecting to the power supply via a resistor for regulating the upper limit voltage and connecting the emitter end to the power supply via a resistor for regulating the lower limit voltage to set the maximum and minimum values of the tuning voltage, it is possible to adapt to the conventional circuit. The purpose of the present invention is to reveal a channel selection device that can easily and reliably regulate the sweep range without degrading performance by making only minor design changes.

(Example) The present invention will be specifically described below based on an example shown in the drawings.

Note that although the embodiment has been described assuming the FTZ standard in West Germany, it goes without saying that it can be implemented in the same way for other standards as well.

FIG. 5 shows an embodiment of the tuner 1, in which the received VHF and UHF signals are
After being amplified by the high frequency amplifier 13, the mixer 14
At , it is mixed with the signal input from the local oscillator 15 and converted into an intermediate frequency IF. This signal is further subjected to signal processing similar to conventional methods to reproduce an image. A variable capacitance diode 2 is used as a tuning element in the local oscillator 15, and a tuning voltage output from a tuning section 4, which will be described later, is applied to the diode 2.
By applying Vt, the oscillation frequency of the local oscillator 15 is changed and the reception frequency is changed.

As shown in the first diagram, the tuning section 4 selects the UHF band,
It includes a band switching unit 44 that selects between VHF high band and VHF low band, and a channel switching unit 5 that outputs a tuning voltage Vt corresponding to the selected channel. The upper and lower limits are regulated by the circuit 7 as described later.

The band switching unit 44 includes a number of changeover switches 45 corresponding to the number of selectable channels, and each fixed contact of the switch is connected to a band changeover terminal of the tuner 1, and the sliding contact is connected via a diode 46. Changeover switch 51 of channel changeover section 5
Connect to.

The channel switching section 5 connects one end of a plurality of sets of variable resistors 6, 6 in parallel, and then connects it to a power source 3 that stabilizes the input voltage Vi with a constant voltage diode 31, and the other end is connected to a channel switching switch, respectively. 51
Connect to. The switch 51 is a transistor switch that is turned on in conjunction with the pressing operation of a channel button (not shown), and is implemented as an IC in this embodiment. Further, the sliding electrodes of each variable resistor 6 are connected in parallel via a switching diode 61, and then connected to a tuning voltage regulating circuit 7 and to a power source ₃ via a bias voltage applying resistor R1.

The tuning voltage regulation circuit 7 connects the base end of the NPN type transistor 71 to the channel switching section 5, the emitter end is grounded via the resistor _R2 , and the collector end is connected to the power source 3 via the upper limit voltage regulation resistor section 8.
Connect to. Further, the emitter end of the NPN transistor 71 is connected to the base end via the diode D, and is connected to the power supply 3 via the resistor section 9 for lower limit voltage regulation, and after passing through the filter section C, to the tuner. Connect to the tuning voltage input terminal 18 of No. 1.

In this embodiment, fixed resistors R ₃ and R ₄ are used as the upper and lower limit voltage regulating resistors 8 and 9, but they may be changed to semi-fixed resistors.

However, when the channel switch 51 is in the OFF state as shown in FIG. state. At this time, if all other channel switches 51 are also off, the tuning voltage Vt is not output.

Next, as shown in FIG. 2b, when the channel changeover switch 51 is turned on, a forward voltage is applied to both ends of the diode 61, so the diode 61 is turned on.
The output voltage from variable resistor 6 is on the anode side of
The sum voltage of V ₀ and the forward voltage drop V of the diode 61 is output. When the sum voltage (V ₀ +V _D ) is applied to the base end of the transistor 71, a collector current according to the voltage value flows, and a voltage Vt is output across the resistor R ₂ . Here transistor 7
Letting the base-emitter voltage of 1 be V _BE , the following relational expression holds true.

V ₀ +V _D = Vt + V _BE ∴Vt = V ₀ + (V _D −V _BE ) ...(1) If the values and characteristics of V _D and V _BE are set to be the same in equation (1), both are canceled and the temperature Due to the change V _D ,
Even if the value of V _BE changes, Vt=V ₀ ...(2) and the value obtained by dividing the reference voltage Vz stabilized by the voltage regulator diode 31 by the variable resistor 6.
V ₀ is directly applied to the tuner 1 as the tuning voltage Vt.

Note that the filter capacitor C is for absorbing ripple voltage induced in the tuning voltage input terminal 18.
Furthermore, when the output voltage V ₀ from the variable resistor 6 suddenly changes from a low voltage to a low voltage, the diode D bypasses the charge stored in the capacitor C, thereby increasing the response speed.

Next, when the sliding electrode of the variable resistor 6 is slid toward the lower potential side, the output voltage decreases depending on the sliding position. Here, since the connection point of resistors R ₄ and R ₂ is connected to the emitter terminal of the transistor 71, if the value obtained by dividing the reference voltage Vz by the resistors R ₄ and R ₂ is Vl, then Vl=Vz/ R ₂ + R ₄ × R ₂ ≒ R ₂ / R ₄ × Vz ……(3) (However, R ₄ ≫ R ₂ ), and the voltage at the base end (V ₀ + V _D ) is shown in Figure 2c.
When the voltage falls below Vl, the transistor 71 is turned off and a constant voltage Vl is applied to the tuner 1.

In contrast to the above, as shown in FIG. 2d, the output voltage from the variable resistor 6 is increased, and the transistor 71
As the base current of the transistor 71 is increased, the transistor 71 eventually reaches a saturation region and the collector current Ic stops increasing. As a result, the upper limit of the voltage at the emitter terminal of the transistor 71 is regulated to a value Vh lower by the emitter-collector voltage VCE than the collector voltage _Vc at the time the transistor 71 reaches the saturated state. Here, the voltage at the emitter terminal is defined by the value of the resistor _R3 , as will be described later.

Therefore, depending on the value of resistor _R3 , transistor 7
The upper limit of the emitter voltage Vh of 1 can be regulated.

Adjustment of the receivable frequency range in the assembling process of the above-mentioned channel selection device is performed as follows.

When setting a lower limit for the sweep range in the VHF low band, first determine the lower limit frequency that can clear regulations such as the FTZ standard (in Figure 6, the frequency is 7MHz lower than the E2 channel), and then
From the VHF low band reception characteristics shown in the figure, a lower limit tuning voltage Vl that exceeds the lower limit frequency and makes it possible to receive the lower limit channel E2 is determined.

The lower limit tuning voltage Vl is determined by the resistance R ₄ and the resistance R 4 as shown in equation (3).
Since it is regulated by the ratio of R ₂ , design the resistor R ₄ to satisfy equation (3). As a result, when the variable resistor 6 is turned to its lower limit, the lower limit tuning voltage Vl is applied to the tuner 1.

Further, by adjusting the receiving range of the tuner 1 under the lower limit voltage Vl, the adjustment of the lower limit frequency is completed.

Next, when setting the upper limit of the receivable frequency in the UHF band, the upper limit tuning voltage Vh is determined from the reception characteristics shown in FIG. That is, the upper limit tuning voltage Vh
within the variation range shown by A in the figure (approximately 19V~
If the upper limit tuning voltage is determined to be within the range (approximately 27V), even if the upper limit tuning voltage is the minimum value within the range (approximately 19V), it is possible to receive the upper limit channel E60 of the stationed range,
However, the upper limit tuning voltage is the maximum value within the range (approximately 27V)
However, the regulated value according to the FTZ standard (878MHz)
It never exceeds.

Also, if the upper limit tuning voltage Vh is determined to fall within the variation range shown by B in the figure (approximately 24.5V to approximately 27V), the upper limit tuning voltage will be the minimum value within the range (approximately 24.5V). Also, channel E69 is the upper limit of the station coverage in European countries other than West Germany.
can be received, and there will be no problem in receiving television broadcasts.

Next, as shown in FIG. 2d, the collector current Ic and the collector-emitter voltage _VCE when the variable resistor 6 is turned to its upper limit are determined. The emitter voltage Vh at this time is Vh=Vz−V _CE −Ic×R ₃ ...(4), so the resistance value of the resistor section 8 for regulating the upper limit voltage is
Determine R ₃ from equation (4). As a result, when the variable resistor 6 is turned to the full upper limit, the upper limit tuning voltage Vh is applied to the tuner 1.

Further, by adjusting the reception range of the tuner 1 under the upper limit voltage Vh, the adjustment of the upper limit frequency is completed.

FIGS. 3 and 4 show other embodiments of the present invention, and in the example shown in FIG. 3, the collector end of the transistor 71 is grounded through a resistor _R5 . In this case, the collector voltage Vc is the value obtained by subtracting the voltage drop due to the resistor _R3 from the reference voltage Vz, and the current flowing through the resistor _R3 is the collector current Ic and the resistor _R5.
The _following equation holds true.

Vc=Vz−R _{3 ( Ic} + _Vc / _{R 5Vc} is calculated _{from the} above _{formula . 5} Since there is a relationship of <1, when both sides are multiplied by Ic, the second term in the parentheses on the right side of the above equation becomes Ic・R ₃ /R ₃ +V ₅ <Ic.

Here, if the values of R ₃ , R ₅ , Vz, and Ic are determined in advance so that Vz/R ₃ +R ₅ ≫Ic, then the value of the second term in the parentheses on the right side of the above equation is the first
It is very small compared to the value of the term.

Therefore, Vc≈VzR ₅ /R ₃ +R ₅ (5), and the value of Vc remains constant regardless of the value of Ic, making it easy to set Vc.

In the embodiment shown in FIG. 4, a semi-fixed resistor _R6 is further connected to both ends of the resistor _R3 , thus making it possible to finely adjust the upper limit voltage.

As described above, the present invention includes a resistor at the emitter terminal of the transistor 71 installed in the tuning voltage regulating circuit 7.
By interposing R ₄ to regulate the emitter voltage, the lower limit of the tuning voltage is regulated, and by interposing resistor R ₃ on the collector side to regulate the collector voltage, the upper limit of the tuning voltage is regulated. So,
It can be easily manufactured with only minor design changes to conventional circuits and almost no changes to the production line, and the receivable frequency band can be reliably and easily restricted without any deterioration in performance. , has excellent effects.

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram showing an example of a channel selection device according to the present invention, Fig. 2a is when the channel switch is off, Fig. 2b is when the channel switch is on, and Fig. 2c is the lower limit. Figure 2d is an explanatory diagram showing the voltage regulation situation, and Fig. 2d is an explanatory diagram showing the upper limit voltage regulation situation, respectively.
3 and 4 are electric circuit diagrams showing other embodiments, and FIG. 5 is a block diagram showing an outline of the tuner.
FIG. 6 is a graph showing an example of reception characteristics of a tuner, and FIG. 7 is an electric circuit diagram showing a conventional device. 1... tuner, 2... variable capacitance diode,
5...Channel switching unit, 6...Variable resistor, 6
1... Switching diode, 7... Tuning voltage regulation circuit, 8, 9... Resistance section.

Claims (1)

[Claims] 1 Equipped with a tuner 1 equipped with a variable capacitance diode as a tuning element, and a tuning section 4 that outputs a tuning voltage to be supplied to the variable capacitance diode, the tuning section 4 It is equipped with a plurality of variable resistors 6 that divide the voltage Vz to form a tuning voltage for each reception channel, and the output terminals of each variable resistor are connected to each other via switching diodes 61, respectively.
In the tuning device in which the tuning voltage output terminal of the tuning section 4 is provided at the connection point, a tuning voltage regulating circuit 7 is interposed between the tuning section 4 and the tuner 1, and the tuning voltage regulating circuit 7 is Equipped with an NPN type transistor 71,
The base end of the transistor 71 is connected to the tuning voltage output terminal of the tuning section 4, the emitter end is connected to the tuning voltage input terminal of the tuner 1 and grounded via a resistor, and the emitter end of the transistor is used for lower limit voltage regulation. The collector end of the transistor 71 is connected to the power supply via the first resistor section 9 for regulating the upper limit voltage, and the collector end of the transistor 71 is connected to the power supply via the second resistor section 8 for regulating the upper limit voltage. A tuning device characterized in that an upper limit is regulated, and a lower limit and an upper limit of an output tuning voltage are regulated. 2. The channel selection device according to claim 1, wherein the first resistance section 9 and the second resistance section 8 are fixed or variable resistors. 3. The second resistor section 8 includes a plurality of resistors that divide the reference voltage, and the voltage divided by the resistors is applied to the collector end of the transistor 71. Channel selection device. 4. The second resistor section 8 has a first fixed resistor and a variable resistor interposed in parallel between the collector end of the transistor 71 and the reference voltage point, and
The collector end of the transistor 71 is grounded via a second fixed resistor.
The channel selection device described in section.