JPS587916A - Channel selecting circuit - Google Patents

Abstract

PURPOSE:To suitably take out a signal for driving an AFT (automatic frequency tuning) defeating circuit by mounting a means for obtaining said signal by using the change of voltage generated between both the ends of any one of resistors at the time of the replacement of contents to be preset. CONSTITUTION:When the 1st channel selecting switch SW1 is completely turned on, current flows from a resistor R3 to the earth through a preset switch BS1, a light emitting diode D1 and the 2nd switch (b) and the potential of a line l3 is turned to its low level, so that a switching diode d3 is turned on and the voltage of a point (x) drops down to 2.5V. Consequently a positive pulse like A is generated from a means 10 at the switching of channels and an AFT defeating circuit 5 is actuated during the positive pulse period or a fixed period corresponding to said period to stop applying the AFT voltage formed by an AFT circuit 2 to a tuner 1. By said procedure, a signal for driving the AFT defeating circuit can be suitably taken out at the switching of channels.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a channel selection circuit for a television receiver or the like.

The new type of tuning circuit disables AFT (automatic fine tuning) when switching channels! A signal for driving a defeat circuit is obtained in response to channel switching, and the present invention proposes a channel selection circuit that can extract such a signal very suitably.

The following will explain the embodiments shown in the drawings.

In the figure, (1) is a tuner with a tuning voltage input terminal (Tu) and a VHF band switching voltage input terminal (8).
, UHF operating voltage input terminal (U), and VHF operating voltage input terminal (V). ) and generates an output according to the frequency shift of the video IP carrier, for example, and automatically controls the local oscillation frequency of the tuner using this output.The output of the four-set AFT circuit (2) is output from terminal f31 (4). Disables when shorted.

(5) acts to short-circuit the terminal F3J (4) when no voltage is applied to the input terminal f(6) (AP
'T Defeat circuit.

(811) (81su...(sWri) is a tuning switch provided for each channel, and the first
It consists of a switch f (a) and a second switch f (b).

It is assumed that the configuration is such that when the tuning switch for one channel is turned on, the tuning switch t for other channels is turned off. The first suite of each channel (one part of the trend is the Botenchonota (Pl) for setting the tuning city LE) (
The other end is connected to the variable terminal of the tuner (!U) of the tuner (11). is connected between the +1 sOV power supply and ground.One end of the second switch (b) is connected to a light emitting diode (Dl) (Dt)...(Dn) for channel display.
), and the other end is connected to ground. Six resistors (RL) (R3) are connected to the +15V power supply line (7), and the other end of this resistor (R1) (R3) is connected to the Brisset spin y- (BSz) (BSs+)...
・The three contacts (V (VH) (U) of (BSn) are connected to each other, among which the U band contact (01 is the resistor (R1)) and the high band contact (V r
) is connected to the resistor (R), and the low band contact L] is connected to the resistor (R). Each preset switch (
The movable piece of BS (BS)... (BSn) is the channel display light emitting diode (Di) (D... (Dn)
) is connected to the anode of the The low band contact of the preset switch (V is also connected to the transistor (Q)
The JHF band contact ([1) is connected to the base of the transistor (Q) via a resistor (Rs). Note that s ('') is a bias resistor.The emitter of the transistor (q) is grounded,
The collector is connected to the power supply (+50V) via a resistor (R11) and directly connected to the band switching heavy voltage input terminal (SJ) of the tuner fil.The above transistor 9 (
The output of qz) is directly connected from the collector to the tuner H terminal (U
E) and the resistor (RLO) (R7) is applied to the base of the transistor (Q).
"CVB) K is supplied to the tuner (1). During low band reception, +15V is applied to the end f(8) [+50V% terminal (V terminal), and the low band receiver (N Ry(CV
B) K + 15V, (B) VCOV ÷ observed value. Mari UHF payment IF? tC Ha (Vl) (!3) Ha OV
% (UB) K+15V power must be given. The band switching circuit (8) consisting of the transistor (QL) and the second switch switch the preset content of one preset switch to the preset content of another preset switch in accordance with the channel selection operation. A first means (9) for acting on the tuner (1) is formed. +101 is an A4T defeat circuit that utilizes the transient change in voltage between the two resistors when changing the preset contents described in IJO. (6) A second means for obtaining No. B for driving, the second means being the resistor (R1) (R
(Riniso tl, zotL-Q sword failed to connect switching da (auto (dl) (di) (dz) and 1)
1j+1s v vv H source uin (IJ and own IJM
It consists of a second resistor (R) that is commonly connected to the seven nodes of the self-contained diodes (dl), (da), and (d3), and its output is obtained from the connection point (a).

Next, the operation will be explained.

Now, we will discuss the case of switching from a state in which all channels other than the first channel are being received to a state in which the first channel is being received. When the song is switched to the first channel, either one of the lines (Zi) (I!S(e)
is at low level, so the switching diode (dx) (ds(d) is turned on (
From point a), only a low level (2.5V) is applied, and the APT defeat circuit (5) does not operate.
Since the f(31 (41) is not short-circuited, the force is formed in the AFTl path (2), and the AFT
The circuit is used without being invalidated (it has an effective effect on the 11 local oscillation circuits).

When I turned on the channel selection switch (SW) to switch to the first channel, the channel selection switch for the channel that had received the UVC signal was opened, so the preset switch and light emitting diode for that channel were brought out and connected to ground. Moreover, the channel selection switch (SW) of the first channel will be turned off until it is turned on completely, so the first channel Although it takes a short time to achieve the reception switching of the channel selection switch (SWz) (
SW... (There is a time when the SW is turned off. Therefore, during that time, no voltage drop occurs on the resistor (R1) (H), and therefore the line (/ l) (
/su(lrihizun (, +15V K&li, switching diodes (dx) (dmaro) (dx) (dx) (all diodes are turned off and the potential at point (a) also rises by +15Vl'.

When the first channel selection switch (SW) is completely turned on, current flows through the path of the resistor (R) → preset switch (BS) → light emitting diode (Dl) → second switch (b) → ground. Since the potential of (c) becomes low level, the switching diode (d) turns on and (a)
The point drops to +2.5v. Therefore, when switching channels, a positive pulse such as the second means 11 (from l to CA) is generated, and the AFT defeat circuit WJ (5) operates only during the positive pulse period or a certain period corresponding to the period, and the AFT defeat circuit WJ (5) is activated. '
T circuit (2) Do not allow the T-formed AFT voltage to act on the tuner.
When the switch is completely turned on, the tuning' magnetic pressure set by the potentiometer (PI) is applied to the terminal (Tu) VC of the tuner (1) through the first switch (a).

Since the reset switch (SW) of the first channel is set to low band, when the first channel is selected, the base of the transistor (Q) becomes low level, the transistor (Q) is turned off, and the tuner (SW) is turned off. ) is given +50V to the terminal (S), and the internal coaxial circuit of the tuner fl) is set to the low band.
Since the voltage is at high level (+15V), the transistor (q) is turned off.

The resistance (RIO) has a relatively small value (1xΩ or less), and the voltage generated at point (B) when the transistor (Ql) is off is low and the LIMP drive voltage is not applied to the end f ([1]. As the k1 point also becomes low, the transistor (q) turns on and a VHF drive voltage is applied to the terminal (VB).
It is also possible to substitute the impedance when looking inside from the terminal (S).

As explained above, according to the present invention, when switching channels, cDAF? This is effective because the signal for driving the defeat circuit can be extracted from the channel selection circuit very suitably.

Another dud F! According to A, a plurality of resistors are connected to the power supply, and a reception band reset switch and a band switching circuit are connected to the other end of the resistor, and a channel switch is connected between the other end of the 10th reset and the reference potential point. Since the display light emitting diode is connected to a series circuit of a switch that operates according to the channel selection operation, the channel display light emitting diode drive switch and the band switching circuit drive switch are connected to the channel selection switch (Six) (8 switches). -... (Sin)'s second switch f (b) is also used, and the first switch (
aJ can be used only for tuning. Therefore, if the first switch (aJ side) is used for starting coaxial voltage extraction and for driving the band switching circuit, a diode is required for each channel to prevent mutual influence between the tuning voltage side and the band switching side. The invention eliminates the need for such diodes.

[Brief explanation of the drawing]

The drawing is a circuit diagram of a channel selection circuit embodying the present invention. (11・-f-L-su* (2+・A r 2 times M%
(5)・A r T defeat circuit, (7)...+
15V power supply line, (9)...first means, cry...second method, (R1)(Rs(Rs)...resistance, (al
l) (Si) (8Wo) --- Channel selection suite, (
BSl) (88m) (BSn)...Reception band preset switch, (dl) (da) (da)--Switching diode, (Dl) (D*) (D3)...
- Light emitting diode for channel display. (RO)...Second resistance.

Claims (3)

[Claims] (1) Connect multiple resistors to the power supply, connect a receiving band preset switch to the other end of this resistor, and change the preset content of one preset switch to the other preset switch according to the channel selection operation. AF? by using a change in the voltage across either of the resistors when switching the preset contents; A channel selection circuit comprising a second means for obtaining a signal for driving a defeat circuit. (2) The second means includes a plurality of switching diodes, one end of which is connected to each connection point of the resistance reset switch, and a plurality of switching diodes, one end of which is connected to a power supply and the other end of which is connected to the other end of the switching diode. 2. The tuning circuit according to claim 1, wherein the tuning circuit comprises a second resistor and an output voltage is generated from a connection point between the second resistor and a switching diode. (3) Along with connecting multiple resistors to the power supply. A reception band reset switch and a band switching circuit are connected to the other end of this resistor, and a channel display light emitting diode and a switch that operates according to the channel selection operation are connected in series between the other end of the reset switch t and the reference potential point. Pre-station circuit formed by connecting circuits.