Transmitter for outputting differential signals of different voltage levels

#1. Field of the Invention

#The present invention relates to a transmitter for differential signaling. More specifically, a transmitter for differential signaling outputting selectable low-voltage currents is disclosed.

#2. Description of the Prior Art

#FIG. 1 is a simple circuit diagram of a differential signal transmitter according to the prior art.

#FIG. 2 is a simple circuit diagram of a differential signal transmitter according to the present invention.

#FIG. 3 is a simple circuit diagram of a control circuit of the differential signal transmitter of FIG. 2.

#Please refer to FIG. 2 of a differential signal transmitter according to the present invention. The transmitter comprises a control circuit 52 and a driver circuit 50 including two electrical sources 54, 56, a ground 72, two transistors 64, 66, two inverted transistors 60, 62, and a resistor 58(R2). The driver circuit 50 also comprises two inputs, the first input receives data and a second input receives inverted data (data bar). The operation of the basic driver circuit 50 of the present invention is well known in the art and functionally similar to the prior art described above.

#The bias supplied by the control circuit 52 controls the inputted current of the current source 54 to fall within a specified range. When the inputted data is set high (thus data bar is set low) transistors 64 and 62 are turned on allowing current to flow from the current source 54 through transistor 62 to a node NB. From the node NB, the current VoutP flows to the resistor 58. From the resistor 58, the current VoutN flows to a node NA and through the transistor 64 and the current source 56 to the ground 72. When the inputted data is low (thus data bar is high) transistors 60 and 66 are turned on allowing current to flow from the current source 54 through transistor 60 to the node NA. From the node NA, the current VoutN flows to the resistor 58. From the resistor 58, the current VoutP flows to the ground 72 via the node NB, the transistor 66, and the current source 56. The outputted current when data is high is equal to VoutP−VoutN which equals I*R2 and corresponds to a “1” in the differential signal. The outputted current when data is low is equal to VoutP−VoutN which equals −I*R2 and corresponds to a “0” in the differential signal.

#FIG. 3 is a simple circuit diagram of an example control circuit 52 according to the present invention. It is understood that there are numerous ways to implement a control circuit for the present invention and FIG. 3 is merely an illustration of only one possible control circuit. The spirit of the present invention applies to any method of using one or more control indicators to combine one or more current sources and output the combined current to be used as an electrical bias for a differential signal driver.