TV DEMODULATOR CAPABLE OF CALIBRATING OUTPUT AND CALIBRATION METHOD THEREOF
The present invention provides a TV demodulator, which includes a TV digital-to-analog converter (TV DAC) and a calibration circuit. The TV DAC includes: a master control switch controlled by a calibration signal to generate a master current; a current distribution circuit distributing the master current to generate an analog output signal at an output terminal; a first switch electrically connected between the current distribution circuit and a first resistor; and a second switch electrically connected between the current distribution circuit and a second resistor. The calibration circuit generates the calibration signal according to the analog output signal, to feedback control the master current.
The present invention claims priority to TW 104108559, filed on Mar. 18, 2015.
BACKGROUND OF THE INVENTION1. Field of Invention
The present invention relates to a TV (television) demodulator capable of calibrating its output and a calibration method thereof; particularly, it relates to such a TV demodulator capable of generating an accurate output signal under a situation where a resistance of a TV transmission wire is unknown, and a calibration method thereof.
2. Description of Related Art
In a conventional TV demodulator, the output signal is often affected by the resistance of the back-end circuit connected to the output of the TV demodulator. In order to generate an accurate output signal, the prior art adopts external add-on resistors, to match with a resistance of a TV transmission wire which is connected to the output of the TV demodulator.
Nevertheless, because the resistance of the TV transmission wire is unknown, the add-on resistors may not always match with the resistance of the TV transmission wire, thus failing to generate the desired accurate output signal. As a consequence, an issue such as that the color level cannot be full level, or other problems, may arise.
The following patents disclose contents which are related to the present invention: U.S. Pat. No. 8,767,129, U.S. Pat. No. 7,352,238 and U.S. Pat. No. 4,544,911.
In view of the above, to overcome the drawbacks in the prior art, the present invention proposes a TV demodulator capable of calibrating its output, and a calibration method thereof. The TV demodulator is capable of generating an accurate output signal under a situation where a value of the resistance of the TV transmission wire is unknown. Besides, the present invention provides two operation modes: a high quality mode and a low power consumption mode, which increases the flexibility in application.
SUMMARY OF THE INVENTIONFrom one perspective, the present invention provides a TV demodulator capable of calibrating output, comprising: a TV digital-to-analog converter (TV DAC), which includes: a master control switch having one end coupled to a predetermined voltage level, the master control switch being controlled by a calibration signal, wherein when the calibration signal turns ON the master control switch, a master current is generated; a current distribution circuit coupled to the master control switch, the current distribution circuit distributing the master current according to an image control signal, so as to generate an analog output signal at an output terminal of the TV demodulator; a first switch and a first resistor coupled to each other in series, wherein the first switch is coupled to the current distribution circuit and the output terminal; and a second switch and a second resistor coupled to each other in series, wherein the second switch is coupled to the current distribution circuit; and a calibration circuit coupled to the output terminal and the master control switch, wherein the calibration circuit generates the calibration signal for controlling the master control switch according to the analog output signal, so as to feedback control the master current.
In one embodiment, under a voltage output mode, the first switch and the second switch are both ON, whereby the TV demodulator provides the analog output signal in a voltage form which has been calibrated.
In one embodiment, under a current transmission mode, the first switch and the second switch are both OFF, whereby the TV demodulator provides the analog output signal in a current form.
In one embodiment, the calibration circuit includes: a comparator for comparing the analog output signal or a signal related to the analog output signal with a reference voltage, to generate a comparison result; and a control circuit for generating the calibration signal according to the comparison result.
In one embodiment, the calibration circuit includes: an error amplifier for comparing the analog output signal or a signal related to the analog output signal with a reference voltage, to generate the calibration signal.
In one embodiment, the TV DAC and the calibration circuit are integrated into one single integration circuit, and the first resistor and the second resistor are both integrated inside the integration circuit.
From another perspective, the present invention provides a calibration method for a TV demodulator, comprising the steps of: (A) providing a TV digital-to-analog converter (TV DAC), wherein the TV DAC distributes a master current via a current distribution circuit, to determine an analog output signal; (B) providing a first switch and a first resistor, which are coupled to each other in series, wherein the first switch is coupled to the current distribution circuit and the output terminal; (C) providing a second switch and a second resistor, which are coupled to each other in series, wherein the second switch is coupled to the current distribution circuit; and (D) feedback controlling the master current according to the analog output signal.
The objectives, technical details, features, and effects of the present invention will be better understood with regard to the detailed description of the embodiments below, with reference to the attached drawings.
The above and other technical details, features and effects of the present invention will be will be better understood with regard to the detailed description of the embodiments below, with reference to the drawings. The drawings as referred to throughout the description of the present invention are for illustration only, to show the interrelations between the apparatus and devices, but not drawn according to actual scale.
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More specifically, the TV DAC 21 includes a master control switch 212, a current distribution circuit 213, a first switch Vctrl1 and a switch Vctrl2. The master control switch 212 is coupled to a predetermined voltage level, for example but not limited to, a positive power supply VDD. The master control switch 212 is controlled by the calibration signal CS. When the master control switch 212 is turned ON by the calibration signal CS, a master current I is generated. The current distribution circuit 213 is coupled to the master control switch 212 and is controlled by an image control signal IS. The current distribution circuit 213 distributes the master current I (i.e., determines the analog output signal AO) according to the image control signal IS. The current distribution circuit 213 is electrically connected to the first resistor R1 through the first switch Vctrl1. The other end of the first resistor R1, which is not electrically connected to the first switch Vctrl1, is connected to a known voltage level, such as a ground level. The first switch Vctrl1 is coupled to the output terminal OUT. Also, the current distribution circuit 213 is electrically connected to the second resistor R2 through the second switch Vctrl1. The other end of the second resistor R2, which is not electrically connected to the second switch Vctrl2, is connected to a known voltage level, such as a ground level. In one embodiment, the TV DAC 21 and the calibration circuit 22 are integrated into one single integration circuit, and the first resistor R1 and the second resistor R2 are both integrated inside the integration circuit.
In the present invention, because the master control switch 212 is controlled by the calibration signal CS, the level of the master current I can be controlled. That is, the master current I can be feedback controlled according to the analog output signal AO, whereby the analog output signal AO is regulated at an accurate value.
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The present invention can operate under different modes by controlling the first switch Vctrl1 and the second switch Vctrl2. In one embodiment, the first switch and the second switch are both ON, whereby the TV demodulator 20 operates under a voltage output mode. In this mode, referring to
In another embodiment, the first switch and the second switch are both OFF, whereby the TV demodulator 20 operates under a current transmission mode. In this mode, referring to
The present invention has been described in considerable detail with reference to certain preferred embodiments thereof. It should be understood that the description is for illustrative purpose, not for limiting the scope of the present invention. An embodiment or a claim of the present invention does not need to achieve all the objectives or advantages of the present invention. The title and abstract are provided for assisting searches but not for limiting the scope of the present invention. Those skilled in this art can readily conceive variations and modifications within the spirit of the present invention. For example, a device which does not substantially influence the primary function of a signal can be inserted between any two devices in the shown embodiments, such as a switch. For another example, the positive and negative input terminals of an error amplifier circuit or a comparator are interchangeable, with corresponding amendments of the circuits processing these signals. In view of the foregoing, the spirit of the present invention should cover all such and other modifications and variations, which should be interpreted to fall within the scope of the following claims and their equivalents.
Claims
1. ATV demodulator capable of calibrating output, comprising:
- a TV digital-to-analog converter (TV DAC), which includes: a master control switch having one end coupled to a predetermined voltage level, the master control switch being controlled by a calibration signal, wherein when the calibration signal turns ON the master control switch, a master current is generated; a current distribution circuit coupled to the master control switch, the current distribution circuit distributing the master current according to an image control signal, so as to generate an analog output signal at an output terminal of the TV demodulator; a first switch and a first resistor coupled to each other in series, wherein the first switch is coupled to the current distribution circuit and the output terminal; and a second switch and a second resistor coupled to each other in series, wherein the second switch is coupled to the current distribution circuit; and
- a calibration circuit coupled to the output terminal and the master control switch, wherein the calibration circuit generates the calibration signal for controlling the master control switch according to the analog output signal, so as to feedback control the master current.
2. The TV demodulator capable of calibrating output of claim 1, wherein under a voltage output mode, the first switch and the second switch are both ON, whereby the TV demodulator provides the analog output signal in a voltage form which has been calibrated.
3. The TV demodulator capable of calibrating output of claim 1, wherein under a current transmission mode, the first switch and the second switch are both OFF, whereby the TV demodulator provides the analog output signal in a current form.
4. The TV demodulator capable of calibrating output of claim 1, wherein the calibration circuit includes:
- a comparator for comparing the analog output signal or a signal related to the analog output signal with a reference voltage, to generate a comparison result; and
- a control circuit for generating the calibration signal according to the comparison result.
5. The TV demodulator capable of calibrating output of claim 1, wherein the calibration circuit includes:
- an error amplifier for comparing the analog output signal or a signal related to the analog output signal with a reference voltage, to generate the calibration signal.
6. The TV demodulator capable of calibrating output of claim 1, wherein the TV DAC and the calibration circuit are integrated into one single integration circuit, and the first resistor and the second resistor are both integrated inside the integration circuit.
7. A calibration method for a TV demodulator, comprising the steps of:
- (A) providing a TV digital-to-analog converter (TV DAC), wherein the TV DAC distributes a master current via a current distribution circuit, to determine an analog output signal;
- (B) providing a first switch and a first resistor, which are coupled to each other in series, wherein the first switch is coupled to the current distribution circuit and the output terminal;
- (C) providing a second switch and a second resistor, which are coupled to each other in series, wherein the second switch is coupled to the current distribution circuit; and
- (D) feedback controlling the master current according to the analog output signal.
8. The calibration method of claim 7, wherein, under a voltage output mode, the first switch and the second switch are both ON so that the TV demodulator provides the analog output signal in a voltage form which has been calibrated.
9. The calibration method of claim 7, wherein, under a current transmission mode, the first switch and the second switch are both OFF so that the TV demodulator provides the analog output signal in a current form.
Type: Application
Filed: Dec 4, 2015
Publication Date: Sep 22, 2016
Inventor: Chia-Ming Wu (HsinChu)
Application Number: 14/960,251