JP2738041B2 - Clamping device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a clamp device for fixing a DC voltage level of an input television signal.

2. Description of the Related Art As a conventional clamping device of a television signal receiver capable of receiving a high-definition television signal and a current standard television signal, for example, a device having a configuration as shown in FIG. 3 can be considered.

In the clamp device shown in FIG. 3, when the television signal supplied to the signal input terminal 3 is a high-definition television signal having a clamp level signal which is a reference signal for a clamp process in a receiver. The signal selection circuit 9 selects the signal subjected to the clamp processing in the first clamp circuit 1 according to the determination signal supplied to the determination signal input terminal 8 and supplies the selected signal to the signal output terminal 7.

At this time, the first clamp circuit 1 clamps the input television signal as described below.

The digital-to-analog converter (hereinafter abbreviated as DAC) 6
The digital external clamp control voltage supplied to the external clamp control voltage input terminal 5 is converted into an analog external clamp control voltage and supplied to a switch (hereinafter abbreviated as SW) 103.

The SW 103 supplies the external clamp control voltage to the resistor 102 during the short-circuit state by the clamp pulse supplied to the clamp pulse input terminal 4 every line, and the potential at the point A is defined by the external clamp control voltage. Operates to clamp to the level.

On the other hand, if the television signal supplied to the signal input terminal 3 is a standard television signal having a negative synchronizing signal, the signal selection circuit 9 sets the potential at the point B in the second clamp circuit 2 to a DC voltage. The signal clamped to the level specified by the voltage source 206 is selected according to the discrimination signal supplied to the discrimination signal input terminal 8 and supplied to the signal output terminal 7.

Here, one end of the resistor 203 is connected to a DC constant voltage source having a negative polarity, and is a leak resistor for supplying a leak current necessary for defining the potential at the point B.

As described above, independent clamp processing is performed on input television signals of different signal systems, and these outputs are switched and transmitted to perform clamp processing according to each system.

However, in the above-described configuration, since both the high-definition television signal having a wide frequency bandwidth and the standard television signal pass through the signal selection circuit, a wideband signal selection is performed. There was a problem that a circuit was required and the device could not be manufactured at low cost.

In view of the problems of the prior art, the present invention eliminates the need for a high-definition television signal to pass through a signal selection circuit, thereby enabling independent television signals of different signal formats to be provided independently of each other. An object of the present invention is to provide a clamp device which can perform a clamp process and is inexpensive and does not cause performance deterioration.

Means for Solving the Problems The present invention provides first clamp means for pulse-clamping a high-definition television signal to a clamp control voltage supplied from the outside according to a clamp pulse supplied from the outside, and a standard television. Second clamping means for clamping a negative peak value of a television signal to a desired DC voltage with respect to a signal, and first and second clamping means according to the type of an input television signal And a signal selecting means for sending one of the outputs of the first and second clamping means to a signal output terminal by the controlling means. It is assumed that.

According to the present invention, with the above-described configuration, for high-definition television signals, the signal selecting means substantially cuts off the connection between the second clamping means and the signal output terminal, and the first clamping means clamps the signal. The control unit controls the processed signal to be supplied to the signal output terminal.

On the other hand, for a standard television signal, the signal selection means substantially inhibits the operation of the first clamp means in a state where the first clamp means and the signal output terminal are connected, and the second clamp means Is controlled by the control means to supply the signal subjected to the clamping process to the signal output terminal.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. However, those having the same purpose and operation as those in FIG. 3 showing a conventional example will be denoted by the same reference numerals and detailed description thereof will be omitted. .

FIG. 1 shows a configuration diagram of a clamp device according to a first embodiment of the present invention. In FIG. 1, when the television signal supplied to the signal input terminal 3 is a high-definition television signal, the SW 103 is supplied to the clamp pulse input terminal 4 according to the determination signal supplied to the determination signal input terminal 8. The coupling between the DAC 6 and the resistor 102 is controlled only by the applied clamp pulse, the SW 204 interrupts the coupling between the capacitor 201 and the signal output terminal 7, and the SW 205
By operating so as to cut off the connection between the first clamp circuit and the signal output terminal 7, the circuit configuration becomes substantially the same as the first clamp circuit shown in FIG. Applied to input television signals.

On the other hand, when the television signal supplied to the signal input terminal 3 is a standard television signal, SW204 and SW205 are short-circuited and SW103 is a DAC according to the determination signal.
The connection between 6 and the resistor 102 is cut off. At this time the capacitor
Capacitor 101 will be coupled in parallel with 201,
The capacitance of the capacitor 201 is sufficiently large compared to the capacitance of the capacitor 101, and the combined capacitance of the capacitor 101 and the capacitor 201 is almost equal to the capacitance of the capacitor 201. With such an operation, the circuit configuration becomes substantially the same as that of the second clamp circuit shown in FIG. 3, and the same clamp processing as that of the second clamp circuit is performed on the input television signal.

As described above, according to the first embodiment, according to the determination signal supplied to the determination signal input terminal 8, the capacitor 201
SW204 that controls the coupling between the signal and the signal output terminal 7 and the SW205 that controls the coupling between the diode 202 and the signal output terminal 7 provide different wideband high-definition television signals without passing through the switch. Independent clamping processing can be performed on the input television signal of the signal system according to each system.

In the first embodiment, the clamp device is configured as shown in FIG. 1, but may be configured as shown in FIG.

In FIG. 2, when the television signal supplied to the signal input terminal 3 is a high-definition television signal, the SW is switched according to the discrimination signal supplied to the discrimination signal input terminal 8.
103 controls the connection between the DAC 6 and the resistor 102 only by the clamp pulse supplied to the clamp pulse input terminal 4, SW204 cuts off the connection between the capacitor 201 and the signal output terminal 7, and SW205 connects the resistor 203 and the signal The connection with the output terminal 7 is cut off. At this time, the signal input terminal 3 and the DC constant voltage source 206
Are coupled via the capacitor 201 and the diode 202, but when a high-definition television signal is received, the potential of the cathode terminal of the diode 202 is always higher than the potential of the anode terminal, and the diode 202 is always It is in cut-off state. Therefore, the coupling between the signal input terminal 3 and the capacitor 201 is substantially cut off, and SW103, SW20
4. By operating SW205 as described above, the circuit configuration becomes substantially the same as the first clamp circuit shown in FIG. 3, and the same clamp processing as the first clamp circuit is performed on the input television signal. Apply.

On the other hand, when the television signal supplied to the signal input terminal 3 is a standard television signal, the discrimination signal causes the switch 103 to disconnect the connection between the DAC 6 and the resistor 102, and
4. SW 205 is short-circuited, and performs the same clamping process as that of the second clamping circuit shown in FIG. 3 on the input television signal in the same manner as in the first embodiment.

As described above, according to the present invention, it is possible to eliminate the need for a high-definition television signal to pass through a signal selection circuit, and to provide independent clamps for input television signals of different signal formats according to the respective formats. Processing can be performed, and the clamp device can be configured at low cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a clamp device according to a first embodiment of the present invention, FIG. 2 is a configuration diagram of a clamp device according to another embodiment of the present invention, and FIG. 3 is a configuration diagram of a conventional clamp device. . 4 ... clamp pulse input terminal, 5 ... external clamp control voltage input terminal, 6 ... digital / analog converter, 8
…… Discrimination signal input terminal, 101, 201 …… Capacitor, 10
2, 203: resistor, 103, 204, 205 ... SW, 202: diode, 206: DC constant voltage source.

Claims (3)

(57) [Claims] A first clamping means for pulse-clamping a first television signal which is a relatively wideband signal; a second clamping means for clamping a second television signal which is a relatively narrowband signal; Control means for controlling one of the first and second clamp means to operate; and a signal for sending one of the outputs of the first and second clamp means to a signal output terminal by the control means. Selecting means, and the signal selecting means is configured to connect the second clamping means with the first clamping means and the signal output terminal coupled to each other.
A clamp device wherein the coupling between the clamp means and the signal output terminal is controlled by the control means. A first capacitor connecting the signal input terminal and the signal output terminal; a first resistor having one terminal connected to the signal output terminal; and an external clamp control voltage input. Digital-to-analog conversion means for performing digital-to-analog conversion on a clamp control voltage supplied to a terminal; and a first resistor provided by a clamp pulse supplied to a clamp pulse input terminal and a discrimination signal supplied to a discrimination signal input terminal. A first switching means for controlling the coupling between the other terminal of the digital input and the digital-to-analog conversion means, and a second clamp means comprising a second capacitor having one terminal coupled to the signal input terminal; A second switching circuit for controlling the coupling between the other terminal of the capacitor and the signal output terminal based on the determination signal; and connecting the anode terminal to the first DC constant voltage source. A combined diode, a third switching circuit for controlling the connection between the cathode terminal of the diode and the signal output terminal by the determination signal, and one terminal connected to the cathode terminal of the diode and the other terminal connected to the negative terminal. 2. The clamping device according to claim 1, further comprising a second resistor coupled to the two DC constant voltage sources. 3. A signal input terminal, wherein one of a first television signal and a second television signal is supplied as an input television signal.
The clamping device as described.