JPH04150419A - Electronic tuner device - Google Patents

Abstract

PURPOSE:To suppress the disturbance on the screen of a TV receiver during the period from the starting of tuning to reception by providing an electronic tuner and AGC voltage controlling section connected to a VIF circuit and forcibly lowering the gain of an RF-AGC voltage by using the IF-AGC voltage of the VIF circuit. CONSTITUTION:When a large TV signal is inputted to the input terminal 1 of an electronic tuner 2, a voltage change outputted from an IF-AGC output terminal 10 is added to an IF-AGC voltage change detection circuit section 20. The voltage change is further added to an RF-AGC voltage control circuit section 21 and a fixed forcible gain reducing voltage is inputted to the RF-AGC terminal 8 of the tuner 2 during a period which is nearly equal to the IF-AGC voltage changing time and controls the RF-AGC voltage for a fixed short period. Therefore, even when a large TV signal is inputted to the electronic tuner, the occurrence of a spurious signal can be suppressed by forcibly lowering the gain of an RF amplifier. In addition, the time required for stabilizing the RF-AGC voltage to a steady state can also be shortened from the conventional example.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electronic tuner device used in television receivers, video tape recorders, and the like.

2. Description of the Related Art In recent years, television receivers and video tape recorders using electronic tuner devices have become widespread.

A conventional electronic tuner device will be described below with reference to the drawings.

FIG. 3 is a block diagram showing a conventional electronic tuner device, and FIG. 4 shows the IFAGC voltage and R during channel selection search.
It is a graph showing a time change of F-AGC voltage.

In Fig. 3, 1 is an input terminal, 2 is an electronic tuner, and 4 is an input terminal.
is the VIF circuit, 5 is the video output terminal, 6 is the hand terminal,
13 is a channel selection control section. Reference numeral 18 denotes a tuning operation unit that controls the electronic tuner 2 and receives television signals. The tuning operation section 18 has an up search button and a down search button, and by operating each button, the electronic tuner 2
Tuning is performed by sequentially increasing or decreasing the tuning voltage. Further, 14 is a band switching circuit, and an input control circuit 15
The VHF band and UHF band are selected under the control of

Next, the operation of actually tuning the television signal will be explained. When a television signal applied to the input terminal 1 of the electronic tuner 2 is received during a search, the synchronization signal from the synchronization signal output terminal 11 of the VIF circuit 4 and the AFT voltage change from the AFT output terminal 12 are transmitted to the tuning control circuit. 16 and output from the tuning voltage sweep circuit 17 to the tuning voltage terminal 7, feedback is applied to the tuning voltage to perform an AFT operation, thereby pulling in a television signal and entering a tuning state.

Problem to be Solved by the Invention At this time, the output from the RF-AGC output terminal 9 of the VIF circuit 4 is connected to the RF-AGC terminal 8 of the electronic tuner 2, and a strong input TV is connected to the input terminal 1 of the electronic tuner 2. If a signal is added, the IF will be
There is a problem in that many spurious signals continue to be output from the output terminal 3, and when attempting to tune in to these spurious signals, normal search and tuning may not be possible.

Next, FIG. 4 shows changes over time in the IF-AC;C voltage and the RF-AGC voltage during the channel selection operation. In FIG. 4, when the electronic tuner 2 starts to tune the television signal during a tuning search operation, the IF-AGC voltage changes according to the magnitude of the television signal, and the gain control in the VIF circuit 4 is performed. (point A), then the voltage of the RF-AGC begins to change (point B), and the gain control of the RF transistor of the electronic tuner 2 is performed to reach a steady state (point 0).

In an actual TV set, the disturbance on the screen disappears because
RF-AC: This is when the C voltage is close to steady state (point D)
, the time T required for channel selection is approximately between point A and point D.

This RF-AGC voltage has a problem in that the larger the television signal, the longer it takes to reach the 0 point, and the longer the disturbance on the screen until it is received.

As described above, in the conventional electronic tuner tuning circuit, when a large TV signal enters the electronic tuner, many spurious signals are output from the IF output terminal 3, and in the worst case, the TV signal If a spurious signal is generated in close proximity to the channel, it may become impossible to select a channel. Furthermore, due to a large TV signal, it takes a long time for the R1''-AGC voltage to reach a steady state, and the disturbance on the TV screen that occurs from the start of channel selection until the TV signal is received becomes longer.

The present invention is intended to solve these problems, and aims to ensure that even when a large television signal is received, and to minimize disturbances on the television screen during channel selection.

Means for Solving the Problems In order to achieve the above object, the present invention provides an AGC voltage control section connected to an electronic tuner and the VIF circuit,
This AGC voltage control section is configured to forcibly reduce the gain of the RF-AGC voltage applied to the electronic tuner during tuning search using the IF-AGC voltage of the VIF circuit.

According to the above-described structure, when the electronic tuner starts tuning the television signal during a channel selection search, the gain of the RF amplifier is forcibly lowered for a predetermined period of time to a value that does not generate spurious signals. This allows normal search and selection without capturing spurious signals, and also minimizes disturbances on the television screen until reception.

Embodiment Hereinafter, an electronic tuner device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an electronic tuner device according to an embodiment of the present invention. That is, FIG. 1 differs from the conventional electronic tuner device shown in FIG. 3 in that an AGC voltage control section 19 is provided. This AGC voltage control section 19 includes an IF-AGC voltage change detection circuit 20 and an RF
-AGC voltage control circuit 21, the IF-AGC output terminal 10 of the VIF circuit section 4 is connected to the IF-AGC voltage change detection circuit 20, and the IF-AGC voltage change detection circuit 2
The output of 0 is connected to the RF-AGC voltage control circuit section 21,
The output of the RFACC voltage control circuit 21 is connected to the RF-AGC terminal 8 of the electronic tuner 2.

The specific operation of this AGC voltage control section 19 will be explained. A large TV signal is input to input terminal 1 of electronic tuner 2.
When the input voltage is input to the IF-AGC output terminal 10, the voltage change output from the IF-AGC output terminal 10 is applied to the IF-AGC voltage change detection circuit section 20, and further applied to the RE, -AGC voltage control circuit section 21, and a predetermined forced gain is applied. Reduced voltage is almost l F-AGC
RF-AC of electronic tuner 2 during the time when the voltage is changing.
RF-AGC is input to C terminal 8 for a certain short period of time.
Control the voltage.

FIG. 2 shows changes in the IF-AGC voltage and RF-AGC voltage over time during a channel selection operation in an embodiment of the present invention. In FIG. 2, when the electronic tuner 2 starts tuning to a large TV signal during a channel search operation, the IF-AG
The C voltage changes to control the gain in the VIF circuit 4 (A
point), the IF-AGC voltage change is detected almost simultaneously and the AG
The RF-AGC voltage begins to change by the C voltage control section 19 (point B), lowers the RF-AGC voltage for a certain period of time (point D), then the RF-AGC voltage begins to change from point D, and the RF The gain of the transistor is controlled and a steady state is achieved (0 point). In an actual television set, the disturbance on the screen disappears when the RF-AGC voltage is close to a steady state (point D), and the time T required for channel selection is between point A and point D, and in this example This can be reduced to approximately half or less compared to the conventional example.

Effects of the Invention As is clear from the above embodiments, the present invention includes an AGC voltage control unit connected to an electronic tuner and the VIF circuit, and this AGC voltage control unit controls the VIF during a channel selection search.
By detecting a change in the IF-AGC voltage from the IF circuit, the gain of the RE-AGC voltage applied to the electronic tuner is forcibly reduced for a predetermined period of time from the time of tuning operation.

As a result, even if a large TV signal enters the electronic tuner, the gain of the RE amplifier can be forcibly reduced to suppress the generation of spurious signals, and smooth tuning search can be performed without capturing spurious signals. . Also RE
-The time it takes for the AGC voltage to reach a steady state is also
By using the voltage control section, the time can be made shorter than before, and disturbances on the television screen that occur from the start of channel selection until the reception of the television signal can be shortened.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an electronic tuner device according to an embodiment of the present invention, and FIG. 2 is a diagram showing the IF-AGC voltage and RE- when tuning and searching is performed by the electronic tuner device according to an embodiment of the present invention. Characteristic diagram showing temporal changes in ACCI pressure, 3rd
The figure is a block diagram showing the configuration of a conventional electronic tuner device.
FIG. 4 is a characteristic diagram showing temporal changes in the IF-AGC voltage and the RE-AGC voltage when performing a tuning search using a conventional electronic tuner device. 1...Input terminal, 2...Electronic tuner, 3...IF output terminal, 4...VIF
Circuit, 5...Video output terminal, 6...
Band terminal, 7... Tuning voltage terminal, 8...
...RE-AGC terminal, 9...RE-AGC
Output terminal, 10... Tsukasa F-AGC output terminal, 11
...Sync signal output terminal, 12...AF
T output terminal, 13...Tuition selection control section, 14...
...Band switching circuit, 15...Input control circuit, 16...Tuition selection control circuit, 17...
Tuning voltage sweep circuit, 18...Tuning selection operation section, 19
...AGC voltage control section, 20...IF
-A(1;C voltage change detection circuit, 21...RE
-AGC voltage control circuit.

Claims (2)

[Claims] (1) An electronic tuner that receives television radio waves, a VIF circuit that amplifies and detects the intermediate frequency output from the electronic tuner, a tuning control section that controls the electronic tuner to select a channel, and the electronic tuner and an AGC voltage control unit connected to the VIF circuit, and the AGC voltage control unit controls the RF-AGC voltage applied to the electronic tuner during tuning search to the IF-AGC of the VIF circuit.
An electronic tuner device equipped with gain control means that forcibly reduces gain using voltage. (2) The gain control means includes an IF-AGC voltage change detection circuit that detects a change in the IF-AGC voltage of the VIF circuit, and an RF
-AGC voltage control circuit, and configured to supply the output of the RF-AGC voltage control circuit to an RF-AGC terminal of the electronic tuner.