JPS63206020A - Receiver - Google Patents

Abstract

PURPOSE:To prevent malfunction just after the changeover by attenuating a tuning voltage at each band from a normal voltage for a defeat period only in switching a reception channel so as to decrease the oscillation frequency of a local oscillator. CONSTITUTION:In depressing, e.g., a switch (SW) SA1 for channel changeover, an input terminal ki of a transmission station control circuit 4 goes to an H level and the oscillation circuit 4a is started. Then the output of the oscillation circuit 4a is counted (4b), decoded (4c) to retrieve transistors (TRs) Q1-Qn, and when a TR Q1 is turned on, the terminal ki goes to an L level and the oscillator 4a is stopped, but the on-state of the TR Q1 is held. A defeat pulse is generated (4e) during the oscillation continuity, a TR Qc is turned on, diodes Dl, Dh, Du are conductive depending on the L, H or U state of VHF of the reception band, thereby decreasing the supply voltage to a band voltage genera tion circuit 5 from the normal value. The supply voltage to an electronic TV tuner 1 is lowered to decrease the local oscillating frequency from the normal value. Thus, malfunction just after band changeover is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a receiving device equipped with an electronic television tuner, such as a television tuner device for a television receiver or a video tape recorder.

[Conventional technology]

Conventionally, this type of receiving device equipped with an electronic television tuner transmits the tuning voltage and band voltage of the reception channel selected by preset tuning from a tuning control circuit formed by a tuning integrated circuit or a microcomputer to the television. The voltage applied to the variable capacitance diode for channel selection provided in the tuner's local oscillation circuit is controlled by the tuning voltage and band voltage, and the local oscillation frequency of the local oscillation circuit is set to the video carrier frequency of the receiving channel. control and perform reception tuning.

Note that the band voltage is the low range of the VHF band (hereinafter referred to as VHF-L).
,! This is a voltage that indicates the difference between the VHF band (referred to as VHF-HF band), VHF-HF band (referred to as VHF-■), and UHF band, and the bias voltage of the variable capacitance diode is switched, for example, and the reception band of the TV tuner is switched by this voltage. .

In addition, this type of receiving device usually has an automatic frequency control (hereinafter referred to as AFC) function, for example, an AFC voltage with a figure-8 characteristic obtained by frequency discrimination of a video intermediate frequency signal of a video intermediate frequency amplification circuit. , supplies the TV tuner,
The local oscillation frequency is pulled to the tuning frequency, that is, the frequency at which the AFC voltage becomes O, and the tuning deviation is corrected.

By the way, based on the switching of the receiving channel, the tuning voltage and band voltage of the switched channel are supplied to the TV tuner in advance of the appropriate AFC voltage, and at this time, the audio carrier wave of the TV broadcast is approximately 45 MHz above the video carrier wave. exists, and AF is also performed by audio carrier waves.
Since the O voltage changes in a figure-8 characteristic, especially when switching from a low frequency channel to a high frequency channel, the receiving frequency of the TV tuner may be lower than the video carrier wave of the switched receiving channel based on the tuning voltage and band voltage. If the frequency is shifted to a high frequency, the receiving frequency of the television tuner will be pulled into the frequency of the audio carrier wave by the AFC voltage, and there is a risk of malfunction.

Therefore, for example, Japanese Patent Publication No. 54-25981 ([0
8B12O3), when switching to receive channel I,
It is described that the above-mentioned malfunction can be prevented by once setting the tuning voltage to 0 and then gradually increasing it to the voltage of the reception channel switched by the RC integration circuit, and generating it later than the AFC voltage.

Also, depending on the receiving device, when switching the reception channel, the default pulse is used for a preset default period, that is, a period slightly longer than the period from when the channel selection operation is performed until the operation of the TV tuner stabilizes. (Due to the operation of the AFC default circuit, AFO'l [
The pressure is cut off to prevent the above-mentioned malfunction.

[Problem that the invention seeks to solve]

By the way, as stated in the above publication, when switching the receiving channel, if the tuning voltage is set to -HO and then gradually raised, reception of the switched receiving channel is performed and the receiving screen of the channel is written. Number≠≠
It takes time for the screen to appear, that is, for the screen to rise.Especially, if an RC filter for ripple smoothing is inserted in the TV tuner's tuning voltage supply line, the screen will rise very slowly. There is a problem in that it is not possible to quickly select a receiving station.

Furthermore, since the time required for the tuning voltage to reach the prescribed voltage of the receiving channel from 0 is constant, there is also the problem that the time required for the screen to rise varies depending on the receiving band.

On the other hand, when the AFO voltage is cut off by the kFOf≠feet circuit, it is necessary to provide the receiver with a complicated circuit such as an AFC dekifeet circuit, and in this case, there is a problem that the configuration becomes complicated.

[Failure to solve the problem]

This invention was made with the above points in mind,
Supplying the tuning voltage and band voltage of the reception channel selected by preset tuning to an electronic television tuner, controlling the local oscillation frequency of the tuner to the set frequency of the reception channel, and responding to the tuning deviation of the tuner. In the receiving device, an automatic frequency control voltage that changes according to a figure-of-eight characteristic is supplied to the tuner, and the oscillation frequency is pulled into the tuning frequency by the control voltage. Defeat period setting means for setting a certain Defeat period that is slightly longer than the period until the tuner starts operating stably for each channel selection operation; This is a receiving device characterized by comprising: tuning voltage attenuation means for controlling attenuation by the amount of attenuation.

[For production]

Therefore, when the receiving channel is selected and the receiving channel is switched, the tuning voltage is attenuated by a certain amount set for each band only during the default period to prevent malfunction. It is possible to perform reception selection quickly in a shorter time than by gradually increasing the tuning voltage from 0 through integration, etc., and because it does not cut off the automatic frequency control voltage, that is, AFC [pressure].
The device is formed without providing a complicated circuit such as a C-defeat circuit.

〔Example〕

Next, the present invention will be explained in detail with reference to FIGS. 1 to 7 showing embodiments thereof.

(First Example) First, FIGS. 1 to 8 showing the first example will be described.

In Figure 1, (υ is an electronic TV tuner,
Tuning voltage input terminal (tu) and ■HF-L
IIF-HUHF input terminals (Jb), (hb), (ub) of respective hand voltages and video intermediate frequency signal (
(hereinafter referred to as VIP signal) output terminal (if) and A
It has an input terminal (af) for the FC voltage, and an input terminal (tu
) of f, :L-ning voltage and input terminal (hb),
Based on the band voltages of (l!b) and (ub), the capacitance of a variable capacitance diode for tuning provided in the internal local oscillation circuit is controlled, and the local oscillation frequency is controlled to the frequency of the receiving channel. In addition, the input terminal (af) A
The capacitance of the diode is finely corrected by FCl [pressure, the tuning deviation is corrected, and the VI of the receiving channel is
The P signal is output from the output terminal (a'').

(2) is a video intermediate frequency amplification circuit to which the VIP signal of the output terminal (af) is input, which amplifies the VIP signal and outputs it to the subsequent video processing circuit and audio processing circuit.

(3) is the AF to which the VIP signal of the amplifier circuit (2) is input.
This is a C voltage generation circuit, which discriminates the frequency of the VIP signal and outputs, for example, an AFC voltage having a figure-8 characteristic shown by the solid line a in FIG. 2 to the input terminal (af).

(4) is a tuning control circuit formed using a tuning integrated circuit (manufactured by NEC Corporation) with model number μPCl368C (manufactured by NEC Corporation), which outputs N tuning outputs corresponding to N reception channels that can be preset. Terminal (kt),...

(kn), has one key input terminal (ki) and a default terminal (df), and is internally connected to the input terminal (ki), including an oscillation circuit (4B), an up/down counter (4b), and a decoder circuit. (40), and N transistors for switching (Ql)
, ..., (Qn), a tuning output circuit (4d),
A default pulse generation circuit (4e) is provided.

(8Al), ..., (SAn) are N tuning switches provided for each receiving channel, and each switch (
One end of 8A+) to (SAn) is the output terminal (kt) to (
kn), and each switch (8
The other ends of A+) to (SAn) are connected to the input terminal (ki).

(VRt), ..., (VRn) are N variable resistors for presetting the tuning voltage of each receiving channel, and one end of each resistor (VBa) to (VRn) is connected to the power supply terminal (+Ba) of aOV. and each resistance (VRt) ~(
The other end of VILn) is connected to each switch (8A+) to (8An
) connected to one end of each.

(Qa) is a transistor for outputting the tuning voltage, and the base is connected to N diodes (DA+
), -..., (DAn) are connected to the sliding pieces of each of the resistors (VRl) to (VRn) via their respective terminals and cathodes, and their collectors are connected to the power supply terminal (+Ba), The emitter is grounded via a resistor (Ra).

(几b) is the power supply terminal (+Ba) and the transistor (QB)
), a bias resistor provided between the base of (R
e) is the emitter of the transistor (Qa) and the input terminal (
tu).

(8Bt), ..., (SBn) are N changeover switches for band setting of each reception channel, and each
fiF-L Vl-IF-f-I UHF contact (
1), (h), and (u). (Lt),・
-, (Ln) are N light emitting diodes for displaying the selection of each reception channel, and each of the diodes (Ll) to (Ln
) is connected to each sliding piece of each resistor (SB+) to (8Bn), and each diode (L
Each cathode switch (SAD) to (Ln) from l) to (Ln)
sArl).

(5) is a band voltage generation circuit that generates the band voltage of each reception channel, the input terminal <ie> is connected to the contact 1') of each switch (8B+) to (8Bn), and the input terminal (ih) is The input terminal (iu) is connected to the contact (h) of each switch + (SB+) to (SBn), and the input terminal (iu)
(8B+) is connected to the contact point (u) of (SBn) and output terminals (ol) and (oh).

The band voltages of VHF-L, VHF-f(, and UHF) are output from (Ou) to input terminals (Jb), (hb), and (ub), respectively.

(QC1j is a transistor for tuning voltage attenuation, the pace is connected to the default terminal (df), and the emitter is grounded.

(fLJ), (Rh), (几U) are three resistors for setting the attenuation amount, and each resistor (f'LJ), (Rh),
One end of (Ru) is connected to the 12VC1 power supply terminal (+Bb), and the other end of the resistor (几l) is connected to each switch (
The other end of the resistor (ah) is connected to each switch (SBl) to (SBn).
The other end of the resistor (Ru) is connected to the contact (u) of each switch (8B+) to (SBn).

(1)II), (Dh), and (1)u) have 7/- nodes as their respective resistances (Re) and (Rh).

There are three diodes for backflow prevention connected to the other end of (Ru), and each diode (DJ'), (Dh
).

The cathode of (Du) is connected to the collector of transistor (QC).

Note that the generation circuit (4e) forms a default period setting means, and resistors (R#), (Rh),
(Ru), diode (DJ), (Dh), (Du
) and the transistor (Qc) form the tuning voltage attenuation means.

Also, depending on the preset settings for each reception channel, each switch (SB+) to (SBn) is set to reception channel I, and contacts (4'), (h),
(u), each resistance (Was) to (Vf
The sliding piece Ln) is set to move to the tuning voltage position of each receiving channel.

On the other hand, in the control circuit (4), while the input terminal (ki) is at a high level, the oscillation circuit (4a) oscillates and the counter (4b) consisting of a ring counter counts the oscillation signal of the oscillation circuit (4a). , the output circuit (4d) is output by the decoder circuit (4C) based on the counting data of the counter (4b).
Each of the transistors (Ql) to (Qn) is turned on in turn.

Then, each transistor (Ql) to (Qn) corresponds to an open transistor (Ql) to (8An).
Qn) is turned on, the input terminal (ki) is inverted to the low level of the ground level, and the oscillation circuit (4a) stops oscillating. At this time, based on the output of the decoder circuit (4C), Switch (SAD) ~ (8An
) corresponding to transistors (Ql) to (Qn) are kept on.

In addition, in synchronization with the start of oscillation of the oscillation circuit (4a), the generator circuit (4e) is connected to the transistor (QC) via the default terminal (d'') for a preset fixed deficit period, that is, as shown in FIG. A high-level default pulse is output for a period T shown in (a).

Then, in order to switch the reception channel, for example, when a switch (SAD) is pressed and turned on, the transistor (Ql) corresponding to the switch (8A+) is turned on.
) is not on, the input terminal (ki) is inverted to high level, the oscillation circuit (4a) is started to oscillate, and each transistor (Q
l ) to (Qn) are turned on in order to search for a reception channel, and when the transistor (Ql) is turned on, the input terminal (ki) becomes low level and the oscillation circuit (4a)
oscillation is stopped and the transistor (Ql) is kept on.

On the other hand, when the oscillation circuit (0) starts oscillating, the generation circuit (0) starts oscillating.
A default pulse is output from 4e) to the base of the transistor (QC) via the default terminal (df), and the transistor (QC) is turned on.

By the way, if only the transistor (Ql'') is turned on by turning on the switch (SAD), then at this time,
Since the switch (8Bl) is switched to the contact (h) as shown, current flows from the power supply terminal (+Ba) to the transistor (Ql) via the resistor (VR+) based on the transistor (Ql) being turned on. In addition, from the power supply terminal (+Bb) to the resistor (Rh) and switch (8B+)
contact point (h).

Current flows into the transistor (Ql) via the diode (L+) and (DBt).

Then, the voltage of the sliding piece of the resistor (VRI) becomes the base voltage of the transistor (Qa), and a tuning voltage corresponding to the voltage of the sliding piece of the resistor (VR+) is generated at the emitter of the transistor (Qa). A tuning voltage is input to the input terminal (tu) via a resistor (Re).

In addition, the diode (L+) lights up to display the selected receiving channel, and the diode (Ll) lights up to display the selected reception channel.
The generation circuit (
The input terminal (ih) of 5) becomes low level, and a preset band voltage of V) IF-H is output from the output terminal (Oh) of the generating circuit (5) to the input terminal (hb).

Then, based on the tuning voltage of the input terminal (tu) and the band voltage of the input terminal (hb), reception of the reception channel of the switch (8A+) is performed by the tuner (υ).

However, as described above, when the switch (SAD) is turned on, the transistor (QC) is also turned on for the period T of the default pulse.

Then, when the transistor (QC) turns on, the current flows through the resistor (fat) to the diode (Dh) and l-transistor (Qe) circuit, and at this time, the voltage at the anode of the diode (Ll) becomes The voltage in one direction of the diode (Dh) decreases to the saturation voltage between the collector and emitter of the transistor (QC), and the tuning voltage output from the emitter of the transistor (Qa) is attenuated compared to when the transistor (QC) is off. As well as decreasing
The diode (Ll) is kept off.

Note that the band voltage output from the generation circuit (5) does not change when the transistor (QC) is turned on.

Since the tuning voltage of each receiving channel is set to be the normal tuning voltage when the transistor (QC) is turned off, the period T in Fig. 8(a) when the default pulse is output is By turning on the transistor (QC), the tuning voltage changes from the normal voltage to the resistance (R1), (
Attenuation control is performed by a voltage set by the resistance value of each of Rh) and (Ru), that is, a certain amount of voltage set for each band.

In addition, FIG. 3(b) shows the case where the tuning voltage is switched from a high channel to a low channel, and the solid lines α, β, γll1VHF-L, VHF-EI, σHF in the figure
The cases of each band are shown below.

Incidentally, the period T is set to be a little longer than the period from when the tuning voltage and the band voltage are applied until the tuner (1) starts operating stably.

Also, since the amount of change in the local oscillation frequency with respect to the tuning voltage differs for each band, the resistance CB, l).

Based on the selection of the resistance values of (Rh) and (Ru), the amount of attenuation of the tuning voltage during period T is such that the local oscillation frequency is reduced from the normal frequency of the receiving channel by a very small amount that is almost the same, regardless of the receiving band. , AF (, is set so that malfunction due to voltage, for example, pulling to point A in FIG. 3(a) does not occur).

Therefore, when each switch (SAI) to (SAn) is pressed to switch the reception channel, the tuner (1) starts to operate stably from the operation settings of the reception channel based on the default pulse output from the generation circuit (4e). The transistor (Q
C) is turned on, and during the period T, the tuning voltage supplied to the tuner (1) is attenuated from the normal voltage by a certain amount set for each band, and at this time the local oscillation frequency is changed to, for example, The voltage changes from a voltage lower than point B in b) toward point B, and the local oscillation frequency of the tuner (IJ) is not pulled into the frequency at point A, thereby preventing malfunction.

Furthermore, after the period T has elapsed, the transistor (QC) is turned on, a regular tuning voltage is applied to the tuner (υ), and one of the diodes (Ll) to (Ln) is turned on to light up the receiving channel. Is displayed.

When switching the receiving channel, the tuning voltage is attenuated by a certain amount set for each band for a period T to prevent malfunctions, so for example, the tuning voltage is set to 0 once and then gradually increased by C-integration. It is possible to quickly select a reception station regardless of the reception band in a shorter time than by setting the AFC voltage, and there is no need to defeat the AFC voltage. ?)
, (fLh).

(mu), diode (DI), (Dh), (Du)
It can be formed by providing a d-radial simple circuit.

In addition, since the diodes (Ll) to (Ln) corresponding to the receiving channel turn on and off by turning on and off the transistor (Qe), the period T from the switching of the receiving channel
When the receiving channel starts normal reception after
~(Ln) lights up, and due to the attenuation control of the tuning voltage, the diode (L+) ~(Ln) point.

You can also control the lights to turn off at the same time for accurate display.

(Second Embodiment) Next, FIG. 4 showing a second embodiment will be described.

In Fig. 4, the same symbols as in Fig. 1 indicate the same or equivalent parts, and the difference is that each diode (LB,
In order to keep the light amount of ~(LBn) constant, a current limiting resistor (Rz) and a backflow prevention diode (Dz) are added.

A series circuit of a resistor (Lz) and a diode (Dz) is provided between the power supply terminal (+Bb) and the collector of the transistor (QC), and each diode (LBz) ~
(LBn) (D 7 /- is the resistance (Rz), die,
t -1' (DZ) 17) connection point, and the switching pieces of each switch (8B+) to (SBn) are connected to the NOR node of diodes (DBt) to (DBn).

Therefore, during the period T when the transistor (QC) is on, the tuning voltage is equal to the resistance (fLl), (Rh
).

The attenuation is controlled by a certain amount for each band set by each resistance value of (Ru), and after the period T has elapsed, the tuning voltage returns to the normal voltage.

In addition, after the period T in which the transistor (QC) is turned off, the diode (LBz) corresponding to the receiving channel
A current flows through the resistor (Rz) through the diodes (LBz) to (LBn), and the diodes (LBz) to (LBn) light up with a constant amount of light regardless of the reception band.

That is, in the case of FIG. 4, the same effect as in the case of FIG. 1 can be obtained, and the diodes (LB,) to (LBn
) has the advantage that it lights up with a constant amount of light regardless of the reception band.

In addition, in the above embodiment, each of the diodes (LB,) to (L
Although a dedicated resistor (RZ) is provided to turn on the resistor (Rz), any one of the resistors (RN), (Rh), and (Ru) can be used instead of the resistor (Rz).

(Third Embodiment) Next, FIGS. 5 to 7 showing an eighth embodiment will be described.

In FIG. 5, (6) is an electronic television tuner that performs reception selection by voltage synthesizer type tuning control using a microcomputer, and the input terminals (tu) and (l) shown in FIGS. !b), (hb), (ub)
, (af).

Input terminal <tu>', (g
b)', (hb)', (ub/.

(af)', an output terminal (if)', and an input terminal (t
The tuning voltage output from the low-pass filter (7) is applied to the input terminals (11b)', (ht
)) The band voltages of the output terminals (Oe)', (Oh)', and (Ou)' of the band voltage generation circuit (8) are applied to ', (ub)', and the output terminal (ifj' is applied to the amplifier circuit). The tuning voltage of the reception channel is output to (2), and the A of the generation circuit (3) is output to the input terminal (af)'.
FCN pressure can be applied.

(9) is a microcomputer for channel selection control, and is a tuning voltage that is input during presetting.

Band voltage data is input to the input terminals (pt) and (pb), respectively, and based on the memory control signal of the control terminal (cd), it is stored in the memory aQ via the address and data terminals (ad). In addition to writing tuning voltage and band voltage data, the pulse width modulation signal and band of the tuning voltage of the receiving channel are written based on the receiving channel number data or up/down data input to the channel control terminal (CHD) during preset reception. Voltage command data is output from the tuning data terminal (td) and bunt data terminal (lxi) to the generation circuit (3) and filter (7), respectively.

The microcomputer (9) has built-in defeat period setting means and tuning voltage attenuation means, and when switching channels, the preset defeat period,
That is, for the period T, the tuning voltage data output from the data terminal (td) is attenuated by a certain amount set for each band.

By the way, the tuning voltage data consists of 14-bit digital data, and based on this data, ao/2
A pulse width modulation signal (hereinafter referred to as PWM signal) with a tuning voltage of 30 to Ov varying in units of v/l sterano is transmitted from the data terminal (td) to the filter (7).
is output to.

Furthermore, the band voltage data consists of 2-bit digital data, and this data is output from the data terminal (bd) to the generation circuit (8) as band voltage command data, and at this time, the generation circuit (8) VHF-L, VHF-H based on the command data code.

The terminal (06)', (oh)', (Ou) corresponding to the identified band is identified.
)' to output the band voltage.

At the time of presetting, the microcomputer (9) filters (7) the PWM signal of the tuning voltage and command data of the band voltage based on the data input to the input terminals (pt) and (Pu). ), and input the reception frequency of tuner (67) to the input terminal (pt).

(1) In addition to controlling the frequency based on the data of u), automatic control or manual control based on AFC voltage etc. is performed when the tuning point is reached according to changes in the data of input terminals (T), t), and (4). Writes the tuning voltage and band voltage data at that time to the specified address of the memory OG, that is, the address of the specified receiving channel, and presets the tuning voltage and band voltage data of each receiving channel to the memory QQ. .

Next, in order to perform preset tuning, operate the channel key or up/down key of each receiving channel and input the number data of the desired receiving channel or up/down data of the receiving channel to the control terminal (CHD). The microcomputer operates as shown in FIG.

That is, by inputting data to the control terminal (chd),
Detects the switching of the reception channel and connects the control terminal (CBD)
Based on the control signal, the address of the switched reception channel is output to the memory α0 to access the address, and the tuning voltage and band voltage written to the address are read from the memory α0.

Then, the read band voltage data is transferred to the data terminal (
bd), and the receiving channel band is VHF-L, VH based on the data of the band voltage.
F-H, UHF (7) Izure-t' 6.6 color it
Separately, only during a period T of several m5ec or several tens of m5ec, if the band is V) IF-L, the read tuning voltage data is attenuated by a step and PWM
If it is converted to a signal and is in the VHF-H or UHF band,
The data of the tuning voltage that has been read out is attenuated by c steps and converted into a PWM signal, and the PWM signal of the tuning voltage that is attenuated by a certain amount set for each band from the regular tuning voltage is sent to the data terminal (t
Output from d).

Furthermore, when the period T has elapsed, the tuning voltage read from the memory GO is directly converted into a PWM signal, and the PWM signal of the regular tuning voltage is transmitted to the data terminal (td
).

Then, the PWM signal of the data terminal (td) is filtered (
7) into a tuning voltage, and the tuning voltage is applied to the input terminal (tu)';
Based on the command data of the data terminal (bd), the terminal (04) corresponding to the band of the receiving channel of the generating circuit (8)
')', (Oh)', (Ou)' No band voltage is input terminal (4?b)'.

(hb)', (ub)', and at this time, the tuner (6I) is applied to input terminals (lb)', (hb)', (u
The reception band is set to the band voltage of b)', and the local oscillation frequency is controlled by the tuning voltage of the input terminal (tu)'.

Therefore, in the case of FIG. 5 as well, when switching the reception channel, the tuning voltage applied to the tuner (61) is changed from the normal voltage by a fixed amount set for each band for a period T, as shown in FIG. , and the local oscillation frequency is controlled slightly lower than the normal frequency, so that the AFC voltage rises from a voltage lower than point B in Figure 2, for example, and becomes equivalent to the AFCl [pressure being defeated]. , the pull-in to the frequency of point A is prevented, and malfunctions are prevented.

Incidentally, FIG. 7 shows the case of switching from a high frequency channel to a low frequency channel, with solid lines α' and β'.

γ' corresponds to the solid lines α, β, and γ in FIG. 8(b).

Further, Y and N in FIG. 6 indicate affirmation and negation, respectively.

Furthermore, steps a, b, and c are independent of the reception band.
The local oscillation frequency is set to be lower than the normal frequency of the receiving channel by almost the same minute amount, and in the case of FIG. 5, as is clearly small from FIG.
is set to .

Therefore, in the case of Figure 5, the microcomputer (
With the software processing in 9), as in the case of Fig. 1 and the 4th tooth, the tuning voltage at the time of channel switching can be attenuated by the period T to prevent malfunction. There is no need to provide a circuit and an AFC default circuit, and the configuration is simplified.

〔Effect of the invention〕

As described above, according to the receiving device of the present invention, when switching the receiving channel, the tuning voltage is attenuated from the normal voltage by the voltage set for each band during the default period, and the local oscillation frequency is lower than the normal frequency. At the same time, the tuning voltage becomes the normal voltage immediately after the defeat period has elapsed, and the local oscillation frequency is controlled to the normal frequency, preventing malfunctions immediately after switching based on the automatic frequency control voltage and ensuring prompt reception. In addition, the configuration can be simplified by omitting complicated circuits such as a conventional automatic frequency control default circuit.

[Brief explanation of the drawing]

1 to 7 show embodiments of the receiving device of the present invention, FIG. 1 is a wiring diagram of the first embodiment, FIG. 2 is a characteristic diagram of the automatic frequency control voltage in FIG. 1, and FIG. Figure (a), (
b) is a waveform diagram of the default pulse and tuning voltage in Figure 1, Figure 4 is a wiring diagram of the second embodiment, and Figure 5 is a diagram of the third embodiment.
6 is a flowchart for explaining the operation of FIG. 5, and FIG. 7 is a waveform diagram of the tuning voltage of FIG. 5. (υ, (6I...electronic TV tuner, (4)...
・Tuition selection control circuit, (4e)...defeat pulse generation circuit, (9)...microcomputer, (QC)・
・Transistor for reducing tuning, (Re
), (几h), (Ru)...Resistance for setting the attenuation amount.

Claims (1)

[Claims] (1) Supplying the tuning voltage and band voltage of the reception channel selected by preset tuning to an electronic television tuner, controlling the local oscillation frequency of the tuner to the set frequency of the reception channel, and In the receiving device, an automatic frequency control voltage that changes in an S-shaped characteristic according to the tuning deviation of the tuner is supplied to the tuner, and the oscillation frequency is pulled into the tuned frequency by the control voltage. Defeat period setting means for setting a certain Defeat period for each channel selection operation, which is slightly longer than the period until the tuner starts to operate stably with the band voltage; A receiving device comprising: tuning voltage attenuation means for attenuating the voltage by a fixed amount set for each band.