Signal transceiving circuit and noise reduction circuit

A signal transceiving circuit, comprising: a receiver, for receiving a input signal; a transmitter, for transmitting an output signal; and a resistance circuit, for omitting the noise caused by the output signal to the input signal. The resistance circuit comprises: a voltage transferring circuit, for generating a voltage transferred signal, and a voltage dividing circuit, for voltage dividing the voltage transferred signal and the output signal, such that the voltage generated at the receiver is cancelled by the voltage generated by the voltage transferred signal at the transceiver. A noise reduction circuit that can be utilized in this signal transceiving circuit is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal transceiving circuit, and particularly relates to a signal transceiving circuit that can omit the noise caused by nearby transmitters. The present invention also relates to a noise reduction circuit that can be utilized to the signal transceiving circuit.

2. Description of the Prior Art

FIG. 1is a prior art signal transceiving circuit. As shown inFIG. 1, the transmitter101outputs an output signal OS to a receiver105of another transceiving circuit via a cable103, and the receiver107receives an input signal IS via the cable103. However, in a current transceiving circuit, a group consisted of a transmitter101and a receiver107always shares the same transmitting lines, as shown inFIG. 1. In this situation, the transmitter101can be regarded as a nearby transmitter for the receiver107. Such structure will cause the output signal OS to generate noise to the input signal IS, and the quality for the receiver107to receive the input signal IS is also affected.

Some inventions are developed to solve this problem. For example, the U.S. patent with U.S. Pat. No. 6,744,831 has disclosed such technology. As shown in FIG. 3 thereof, this patent utilizes a device 88 to counteract the noise caused by the output signal to the input signal. However, such kind of prior art needs extra circuits and accurate control to omit noise. By this way, a larger circuit area is needed, and design complexity, production cost also increase.

SUMMARY OF THE INVENTION

Therefore, one objective of the present invention is to provide a signal transceiving circuit, which can utilize a simple circuit to counteract with the noise caused by the nearby transmitter. Besides, the present invention also discloses the noise reduction circuit that is utilized in the transceiving circuit.

One embodiment of the present invention discloses a signal transceiving circuit, which comprises: a receiver, for receiving an input signal; a transmitter, for transmitting an output signal; and a resistance circuit for omitting noise that the output signal caused to the input signal. The resistance circuit comprises: a voltage transferring circuit, for generating a voltage transferring signal according to the output signal; and a voltage dividing circuit, for voltage-dividing the voltage transferring signal and the output signal, such that a voltage that the output signal generates at the receiver will be counteracted with a voltage that the voltage transferred signal generates at the receiver.

Another embodiment discloses a noise reduction circuit, which outputs an output signal from a signal outputting source and receives an input signal from a receiver. The noise reduction circuit comprises: a voltage transferring circuit, for generating a voltage transferring signal according to the output signal; and a voltage dividing circuit, for voltage dividing the voltage transferring signal and the output signal, such that a voltage that the output signal generates at the receiver will be counteracted with a voltage that the voltage transferred signal generates at the receiver.

Another embodiment discloses a signal transceiving circuit, which is coupled to a signal input source comprising a first input terminal and a second input terminal. The signal transceiving circuit comprises: a receiver, for receiving an input signal; a transmitter, comprising a first transmitting terminal and a second transmitting terminal, and for transmitting a differential output signal via the first transmitting terminal and the second transmitting terminal; and a resistance circuit, for omitting noise that the output signal caused to the input signal, comprising. The resistance circuit comprises a first resistance device, having one terminal coupled to the second transmitting terminal, and the other terminal coupled to the first input terminal; a second resistance device, having one terminal coupled to the first transmitting terminal, and the other terminal coupled to the second input terminal; a first voltage dividing circuit, coupled between the first transmitting terminal and the first receiving terminal; and a second voltage dividing circuit, coupled between the second transmitting terminal and the second receiving terminal.

Via above-mentioned embodiments, only a resistance circuit is needed to counteract the noise that a nearby transmitter causes to the receiver, thus no complex circuit and tough circuit control. By this way, circuit area can decrease, and the cost for manufacturing and design can decrease.

DETAILED DESCRIPTION

FIG. 2is a circuit diagram illustrating a signal transceiving circuit200according to one embodiment of the present invention. As shown inFIG. 2, the signal transceiving circuit200comprises a transmitter201, a receiver203and a resistance circuit205. The receiver201receives an input signal IS. The transmitter201transmits an output signal OS. The resistance circuit205is coupled to a first input terminal216and a second input terminal218of a cable215. The resistance circuit205can be consisted of resistors, or other active/passive devices having resistance characteristics, to omit the noise that the output signal OS causes to the input signal IS. In this embodiment, the signal transceiving circuit200utilizes a differential signal, thus the transmitter201includes a first transmitting terminal207and a second transmitting terminal209, and the receiver203includes a first receiving terminal211and a second receiving terminal213. However, it does not indicate that the concept of the present invention is limited to be utilized to a signal transceiving circuit utilizing a differential signal.

Additionally, in the embodiment shown inFIG. 2, the cable is a HDMI (High Definition Multimedia Interface) cable. Resistors217,219, which are10ohm in this embodiment, are provided between the transmitter201and the voltage source Vcc. Also, capacitors227and229are provided between the cable215and the resistance circuit205. Additionally, the transmitter201includes two switches223,225and a current source221. It should be noted that, these detail structures are only for example and do not mean to limit the scope of the present invention. For example, the transmitter201can be different kinds of transmitters, and the cable215can be other kinds of cables.

FIG. 3is a circuit diagram illustrating detail structures of the signal transceiving circuit shown inFIG. 2. In this embodiment, the resistance circuit205is consisted of resistors. As shown inFIG. 3, the resistance circuit205comprises a first resistor301, a second resistor303, a third resistor305, a fourth resistor307, a fifth resistor309and a sixth resistor311. A first terminal of the first resistor301is coupled to the second transmitting terminal209, and a second terminal thereof is coupled to the cable215. A first terminal of the second resistor303is coupled to the transmitting terminal207. A first terminal of the third resistor305is coupled to a second terminal of the second resistor303, and a second terminal thereof is coupled to the cable215. A first terminal of the fourth resistor307is coupled to the transmitting terminal207, and a second terminal thereof is coupled to the cable215. A first terminal of the fifth resistor309is coupled to the second transmitting terminal209. A first terminal of the sixth resistor311is coupled to a second terminal of the fifth resistor309, and a second terminal thereof is coupled to the cable215. The second terminal of the second resistor303is further coupled to the second receiving terminal213, and the second terminal of the fifth resistor309is further coupled to the first receiving terminal213.

In one embodiment, the second resistor303has substantially the same resistance value (9K ohm) with the resistance value of the fifth resistor309, and the third resistor305has substantially the same resistance value (5K ohm) with the resistance value of the sixth resistor311. That is, the ratio between the resistance values of the second resistor303and the fifth resistor309, and the resistance value of the third resistor305and sixth resistor309is 9:5. Besides, the first resistor301has substantially the same resistance value (40 ohm) with the resistance value of the fourth resistor307. Also, the equivalent resistors231and233of the cable215are both50ohm. That is, the ratio between the resistance values of the first resistor301and fourth resistor307, and the resistance value of the equivalent resistors231and233is 4:5. The equivalent resistor231is the cable equivalent resistor of looking from the transmitting paths Tx−(301,303,305) into cable. The equivalent resistor233is the cable equivalent resistor of looking from the transmitting paths Tx+(307,309,311) into cable. It should be noted that, in the embodiment shown inFIG. 3, for the resistance circuit205, the transmitter201can be regarded as a signal output source to output the output signal OS to the resistance circuit205. Besides, the cable215can be regarded as a signal input source, to output the input signal IS to the resistance circuit205. It should be noted that the ratio between the resistance values of the second resistor303and fifth resistor309, and which of the third resistor305and sixth resistor309, and the ratio between the resistance values of the first resistor301and fourth resistor307and which of the equivalent resistors231and233can be other values except above-mentioned 9:5 and 4:5. Also, all resistors can be replaced with other active devices that can form resistance (ex. MOSFET).

The following description describes why the embodiment shown inFIG. 3can omit the noise that the output signal OS causes to the input signal IS. Please notes the following embodiment only considers AC component but considers no DC component.

Vtxp and Vtxn are the voltages at the first transmitting terminal207and the second transmitting terminal209.

Since the resistance values of the second resistor303, the third resistor305, the fifth resistor309and the sixth resistor311(5K ohm and 9K ohm) are much larger than the resistance value of the first resistor301, the fourth resistor307and the cable equivalent resistors231,233(40 ohm and 50 ohm), the currents flowing through the second resistor303, the third resistor305, the fifth resistor309can be ignored.
Vcp=−Vtx*R231/(R231+R301)=−Vtx*50/(40+50)  (equation 3)
Vcn=Vtx*R233/(R233+R307)=Vtx*50/(40+50)  (equation 4)

Vcp and Vcn are respectively the voltages at a second terminal of the first resistor301and a second terminal of the fourth resistor307.

Vrxp and Vrxn are respectively the voltages at the first receiving terminal211and the second receiving terminal213.

After that, the equations (1) (3) are substituted to equation (6), and equations (2) (4) are substituted to equation (5).
Vrxp=−Vtx*5K/(5K+9K)+Vtx*50/(40+50)*9K/(5K+9K)=0
Vrxn=Vtx*5K/(5K+9K)−Vtx*50/(40+50)*9K/(5K+9K)=0

By this way, Vtx can be totally omitted, to acquire the result that Vrxp=Vrxn=0.

According to above mentioned description, the noise that the output signal causes at the receiving terminal can be completely omitted.

In view of above-mentioned equations, the first resistor301and the fourth resistor307can be regarded as a voltage transferring circuit, since the first resistor301and the fourth resistor307can transfer voltages (decrease voltages). Such voltage transferring circuit can match the cable equivalent resistors231,233to generate voltages Vcp and Vcn, which are related with the voltage Vtxn at the second transmitting terminal209and the voltage Vtxp at the first transmitting terminal207, at a first terminal of the first resistor301and a first resistor at the fourth resistor307(equations 3, 4). It should be noted, the voltage transferring circuit discussed here is not limited to a single resistance device, any circuit that can cooperate with the cable equivalent resistors231,233to generate a voltage dividing function, should be included in the range of the present application.

Then, the second resistor303, the third resistor305, the fifth resistor309and the sixth resistor311match with each other to generate divided voltages for the voltages Vtxn and Vcn, and the voltages Vtxp and Vcp (equations 5, 6). Thus the divided voltages of the voltages Vtxn and Vcn can be counteracted with each other, and the divided voltages of the voltages Vtxp and Vcp can be counteracted with each other. Therefore, the second resistor303, the third resistor305, the fifth resistor309and the sixth resistor311can be regarded as a voltage dividing circuit. Alternatively, the second resistor303, and the third resistor305can be regarded as a voltage dividing circuit, and the fifth resistor309and the sixth resistor311can be regarded as another voltage dividing circuit, to voltage-divide the voltage transferring signal and the output signal, such that the output signal generated at the receiver can be counteracted by a voltage that the voltage transferred signal generates at the receiver.

The following concept discloses the signals received by the receiver.
Vcp=Vsig(equation 1)
Vcn=−Vsig(equation 2)

Vsig and −Vsig indicate the positive and negative voltages of the input signal In generated at the differential signal transmission line.

Since the resistance values of the second resistor303, the third resistor305, the fifth resistor209and the sixth resistor311(5K ohm and 9K ohm) are much larger than the resistance value of the first resistor301, the fourth resistor307and the cable equivalent resistors231,233(40 ohm and 50 ohm), the currents flowing through the second resistor303, the third resistor305, the fifth resistor309can be ignored.
Vtxp=−Vsig*R217/(R307+R217)=−Vsig*10/(40+10)  (equation 3)
Vtxn=Vsig*R219/(R301+R219)=Vsig*10/(40+10)  (equation 4)

Then the equations (1) (3) are substituted to equation (6), and equations (2) (4) are substituted to equation (5).
Vrxp=Vsig*10/(40+10)*5K/(5K+9K)−Vsig*9K/(5K+9K)=−Vsig*4/7
Vrxn=−Vsig*10/(40+10)*5K/(5K+9K)+Vsig*9K/(5K+9K)=Vsig*4/7

Via these equations, it is clear that the amplitude of the signal received by the receiver203is a ratio to the input signal In, but is not affected by the output signal of the transmitter201.

Via above-mentioned embodiments, only a resistance circuit is needed to counteract the noise that a nearby transmitter causes to the receiver, thus no complex circuit and tough circuit control. By this way, circuit area can decrease, and the cost for manufacturing and design can decrease.