Apparatus and method for determining the voltage level of an input signal

The present invention discloses an apparatus and a method for determining the voltage level of a first signal from a playback device having an interface in compliance with an industrial standard. According to the method, first receive the first signal by a signal receiving pin electrically coupled to a signal transmitting pin of the interface. Then output a first output voltage by processing the first signal by the combination of a first zener diode and a first transistor and a second output voltage by processing the first signal by the combination of a second zener diode and a second transistor. Thus the voltage level of the first signal can be determined according to the first output voltage and the second output voltage.

FIELD OF THE INVENTION

The present invention relates to an apparatus and method for determining the voltage level of an input signal, and more particularly to the apparatus and method that is used in a player with a SCART interface by using zener diodes and transistors.

BACKGROUND OF THE INVENTION

The SCART interface has been widely utilized for the video/audio signal transmission in TV sets or players. For example, the SCART interface is a standardized interface that must be implemented in the TV sets and VCR players for sale in European marketplace.FIG. 1AandFIG. 1Bare diagrams illustrating the SCART interface and its connectors.FIG. 1Ademonstrates a SCART connector10that has 21 connecting pins that includes pins for audio/video signals and pins designated for conveying information that controls the transmission of audio/video signals.FIG. 1Bdemonstrates a SCART socket11that has connecting holes for adapting the corresponding connecting pins on the SCART connector10.

Other than TV sets and players, the SCART interface has been also pervasively equipped in audio/video playback devices or signal conversion devices such as video game consoles, disc players, set-top boxes, or video signal converters. As shown inFIG. 1C, for example, a set-top box12can be used to integrate audio/video signals from various sources for the displaying on a TV set through a plurality of SCART sockets121and122. Users can allow the audio/video signal transmission among SCART sockets by connecting them by a SCART cable. For example, as shown inFIG. 1D, a SCART-to-SCART connection can be made by connecting connectors101and102disposed at two ends of a SCART cable100to a SCART socket141of a TV set14and a SCART socket161of a VCR player16(or a audio/video playback device such as a disc player, video game console, or set-top boxes), respectively.

Among the 21 connecting pins of a SCART connector, one of the pins, the Pin8, has been assigned to convey the information to control the aspect ratio of the displayed image. It allows a TV set to determine the proper aspect ration between different aspect rations including the traditional 4:3 screen and 16:9 widescreen. The TV set that connected with a player via SCART interface receives the controlling signal from the player and determines the aspect ratio the player is using according to EN50049-1 and IEC 60933 industry standards. These standards defined the relationship between the voltage level of the controlling signal on the pin8and the aspect ratio that is currently assigned such that the TV set can display the image with properly settings. The detailed definition of the signal on the pin8, as shown inFIG. 2A, is: if the voltage level is between 9.5V and 12V, the assigned aspect ration is 4:3; if the voltage level is between 4.5V and 7V, the assigned aspect ration is 16:9; and if the voltage level is between 0V and 2V, there is no image signal (inactive source) or no specific aspect ration assigned.

To determining the voltage level of the input controlling signal and the aspect ratio it represents, the simplest and most feasible way is to compare the input controlling signal by multiple comparators and translate the comparing results into digital output that can be further processed by logic circuits. Conventionally, in a SCART interface there were two comparators connected to a SCART socket, and the following logic circuit can determine the voltage level of the input controlling signal according to the combination of the two logic output of the comparators.

FIG. 2Bis a circuit diagram of the implementation of the comparators21and22in the SCART interface20. The negative input of each comparator21and22is connected to a reference voltage, while the positive input is connected to the input signal. According to the definition illustrated inFIG. 2A, the reference voltages can be set as 8.9V and 4V for comparators21and22, respectively. When the input signal is with voltage level between 9.5V to 12V, both comparators output logical “1.” Similarly, if the input signal is with voltage level between 4.5V to 7V, the comparators21and22will output logical “0” and “1,” respectively. And two logical “0s” will be output if the input signal is with voltage level between 0V to 2V. Therefore, the following logic circuit can learn the assigned aspect ration according these logic outputs. For example, when the output is “11,” it means the 4:3 screen; when the output is “01,” it means the 16:9 screen; and when the output is “00,” it means the “inactive” setting.

However, the conventional implementation by using two comparators usually accompanies with higher manufacturing costs. And a low-cost solution with a high precision for detecting the voltage level of the input signal becomes an important issue to be resolved.

SUMMARY OF THE INVENTION

One of the objects of the present invention is to provide an apparatus and method for determining the voltage level of an input signal with low-cost and high precision by using zener diodes and transistors.

The present invention provides an apparatus for determining the voltage level of a first signal from a playback device having an interface in compliance with an industrial standard. the apparatus includes a signal receiving pin electrically coupled to a signal transmitting pin of the interface to receive the first signal, a first zener diode having a first breakdown voltage, where the cathode of the first zener diode is connected to the signal receiving pin, a first transistor having a first forward biased voltage, where the anode of the first zener diode is connected to the base of the first transistor and provide a first output voltage, a second zener diode having a second breakdown voltage, where the cathode of the second zener diode is connected to the signal receiving pin, a second transistor having a second forward biased voltage, where the anode of the second zener diode is connected to the base of the second transistor and provide a second output voltage, and a processor electrically coupled to the first transistor and the second transistor, where the processor can determine the voltage level of the first signal according to first output voltage and the second output voltage.

The present invention further provides a method for determining the voltage level of a first signal from a playback device having an interface in compliance with an industrial standard. According to the method, first receive the first signal by a signal receiving pin electrically coupled to a signal transmitting pin of the interface. Then output a first output voltage by processing the first signal by the combination of a first zener diode and a first transistor and a second output voltage by processing the first signal by the combination of a second zener diode and a second transistor. Thus the voltage level of the first signal can be determined according to the first output voltage and the second output voltage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Refer toFIG. 3A, which is a block diagram illustrating an apparatus for determining the voltage level according to an embodiment of the present invention. A player300includes a SCART interface30allowing the signal transmission among other playback devices in compliance with SCART interface standard. A SCART connector40is connected to a corresponding SCART socket (not shown in the diagram) disposed on the SCART interface30. The SCART interface30is used to receive an input signal and transfer the input signal. The player300further includes a signal converter302electrically coupled to the SCART interface30to receive the input signal and converts the input signal into logic signals that can be processed by the following logic circuits, such as a processor303that can determine the voltage level of the input signal according to the logic value it received from the converter302. According to the present invention, the input signal is the signal on the Pin8of the SCART connector.

FIG. 3Bis a circuit diagram illustrating the signal converter302for determining the voltage level according to an embodiment of the present invention. The signal converter302includes a signal receiving pin301electrically couples to a signal outputting pin401of the SCART interface30to receive the input signal. For example, the pin401is connected to the Pin8of conventional SCART connector that indicating signal relates to the widescreen function switching or the aspect ration of the displayed image. Thus the player300can determine the assigned aspect ration according to the voltage level of the input signal.

Instead of the comparators used in the conventional method, the signal converter302according to the present invention includes components utilized the combination of a zener diode and a transistor to replace a relatively expensive comparator and its reference voltage. Zener diodes can works properly with limited current at its breakdown region when reversed biased and can provide a stable voltage drop across the component, which is known as its breakdown voltage.

As shown inFIG. 3B, the cathode of a first zener diode321is connected to the signal receiving pin301via a resistor311. The Anode of the first zener diode321is connected to the base B1of a transistor331. The emitter E1is connected to the first ground353, and the collector C1is connected to the first power source351via a resistor341. Similarly, a second zener diode322is connected to the signal receiving pin301via a resistor312. The Anode of the second zener diode322is connected to the base B2of a transistor332. The emitter E2is connected to the second ground354, and the collector C2is connected to the second power source352via a resistor342. The resistors311and312can be 10 k Ohm resistors in current embodiment because the industrial standards such as EN50049-1 and IEC60933 explicitly require the input impedance to be at least 10 k Ohm. In the current embodiment, the resistors341and342can also be 10 k Ohm resistors.

Moreover, in the current embodiment, the first zener diode321and the second diode322are designed to have breakdown voltage at 3.3V and 8.2V, respectively. The two power sources351and352are set at 3.3V, and the forward biased voltage of transistors331and the 332 is about 0.7V. Generally, a transistor can be turned on when the base voltage is greater than the emitter voltage by more than the forward biased voltage; otherwise the transistor is turned off. For example, when the transistor331is turned on, the voltage at the collector C1will be pulled close to the voltage at the emitter E1, thus the output voltage V1will be close to 0V. On the contrary, if the transistor331is turned off, the voltage at the collector C1will be pulled up to the power source351, and the output voltage V1will be close to 3.3V. Similarly, the second transistor332can perform substantially the same function as the first transistor331and output a second output voltage V2. Therefore the transistors331and332can convert the input signal into digital form having the logical “1” at 3.3V and logical “0” at 0V for the following logic circuit, such as a processor303, to process. Of course, if it is necessary, the power sources can be designed to have different voltage levels to support different voltage requirement of logical “1” of the following logic circuits. For example, if the following logic system requires logical “1” at 5V, the power sources351and352can also be 5V accordingly.

Then the voltage level of the input controlling signal from the signal outputting pin401can be determined according the combination of the first output voltage V1and the second output voltage V2, and the assigned aspect ration can also be confirmed. The output voltage V1and V2can be seen as logic signals that can be easily processed by the following logic circuits.

As the definition according to the industrial standards, when the input signal is with voltage level between 9.5V to 12V, the assigned aspect ratio is 4:3; when the input signal is with voltage level between 4.5V to 7V, assigned aspect ratio is 16:9; and the input signal is with voltage level between 0V to 2V, it means the “inactive” setting. Now the following logic circuit or processor can learn the assigned aspect ration according to the logic combinations similar to what have been used in the convention arts.

In the current embodiment, two predetermined threshold voltages are designed to be 8.9V and 4V to allow some toleration in signal qualities. When the input controlling signal is between 9.5V to 12V as defined in the industrial standards or any level above 8.9V, the second zener diode322will be negative biased in breakdown region and have an 8.2V voltage difference. The second transistor332will be turned on because there is a 0.7V difference allowed between the base B2and the emitter E2. Thus the second output voltage V2will be about 0V. Similarly, the voltage drop of the first zener diode321allows the first transistor to be turned on and further output a first output voltage V1at about 0V. Then the following logic circuit or the processor303can find the assigned ratio is 4:3 if both output voltages are 0V or the corresponding logic value is “00.”

Similarly, when the input controlling signal is between 4.5V to 7V as defined in the industrial standards or any level above 4V but below 8.9V, the first zener diode321will be negative biased in breakdown region and have a 3.3V voltage difference. The first transistor331will be turned on because there is a 0.7V difference allowed between the base B1and the emitter E1. Thus the first output voltage V1will be about 0V. On the contrary, the second zener diode322is still off and the second transistor332is turned off, either. The collector C2will be pulled high and have a second voltage output V2at about 3.3V. Then the following logic circuit or the processor303can find the assigned ratio is 16:9 if the output voltages V1and V2are 0V and 3.3V, respectively, or the corresponding logic value is “01.”

Moreover, if the input controlling signal is between 0V to 2V as defined in the industrial standards or any level below 4V, both transistors will be turned off and both voltage outputs V1and V2will be at 3.3V. Then the following logic circuit or the processor303can find the assigned ratio is “inactive” setting if both output voltages V1and V2are 3.3V or the corresponding logic value is “11.”

Refers toFIG. 3C, which is a table illustrating the relationship between the voltage level of an input signal and the output logic values according to an embodiment of the present invention. The relationship between the voltage level of the input controlling signal, the output logic values, and the assigned aspect ratio as abovementioned can be further summarized into a table as shown inFIG. 3C. The table cab be further stored in the processor303to allow the processor to determine the assigned aspect ratio appropriately based on the output voltages V1and V2.

FIG. 4is a flowchart further illustrating a method for determining the voltage level according to an embodiment of the present invention. First a signal receiving pin301receives a controlling signal from a signal outputting pin401(Step S1). Then output a first output voltage V1and a second output voltage V2by processing the controlling signal by the combination of a first zener diode321and a first transistor331and the combination of a second zener diode322and a second transistor332, respectively (Step S2). Then convert the first output voltage V1and the second output voltage V2into logic value by a signal converter302(Step S3). Finally, determine the appropriate assigned aspect ratio by the processor302according to a table and the first output voltage V1and the second output voltage V2, or their corresponding logic values (Step S4).

Thus, the present invention can not only determine the voltage level of an input signal with a high precision, but also replace the conventional comparators with relatively cost-saving zener diodes and transistors.