CAN bus driver with symmetrical differential output signals
First Claim
1. A bus driver for transmitting data signals via wires of a bus, which bus driver comprises:
- a first supply terminal (2) and a second supply terminal (4) for the connection of a supply voltage for the bus driver,a first bus terminal (6) and a second bus terminal (12) for the connection of respective wires (8,
14) of the bus,a first transistor (T1) of a first conductivity type having a first main current path connected between the first supply terminal (2) and the first bus terminal (6) and having a first control electrode,a second transistor (T2) of a second conductivity type opposite to the first conductivity type having a second main current path connected between the second supply terminal (4) and the second bus terminal (12) and having a second control electrode, anddrive means (18) for driving the first control electrode and the second control electrode,characterized in that the drive means (18) comprise;
a common node (20),a third transistor (T3) of the first conductivity type having a third main current path connected between the first supply terminal (2) and the common node (20) and having a third control electrode coupled to the first control electrode,a fourth transistor (T4) of the second conductivity type having a fourth main current path connected between the second supply terminal (4) and the common node (20) and having a fourth control electrode coupled to the second control electrode,a first control voltage source (22) connected between the third control electrode and the common node (20), anda second control voltage source (24) connected between the fourth control electrode and the common node (20).
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Accused Products
Abstract
Bus driver having a P-channel output transistor (T1) for driving a first bus terminal (6) from a positive supply terminal (2), an N-channel output transistor (T2) for driving a second bus terminal (12) from a negative supply terminal (4), a P-channel driver transistor (T3) and an N-channel driver transistor (T4) series connected between the positive (2) and the negative (4) supply terminal. The control electrodes of the P-channel transistors (T1, T3) are interconnected and the control electrodes of the N-channel transistors (T2, T4) are interconnected to obtain a fixed relationship between the currents through the P-channel transistors (T1, T3) and through the N-channel transistors (T2, T4). The conduction of the driver transistors (T3, T4) is controlled by two floating control voltage sources (22, 24) which are connected between the interconnection node (20) of the driver transistors (T3, T4) and the respective control electrodes of the driver transistors. Any difference between the current through the P-channel driver transistor (T3) and the N-channel driver transistor (T4) is compensated for by a change in the voltage level at the interconnection node (20). In this way the currents through the driver transistors (T3, T4), and also through the output transistors (T1, T2) which are scaled copies of the driver transistors, are always equal and a highly symmetrical driving of the two bus wires (8, 14) is obtained. As a result, the electromagnetic radiation of the bus wires is low.
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Citations
8 Claims
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1. A bus driver for transmitting data signals via wires of a bus, which bus driver comprises:
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a first supply terminal (2) and a second supply terminal (4) for the connection of a supply voltage for the bus driver, a first bus terminal (6) and a second bus terminal (12) for the connection of respective wires (8,
14) of the bus,a first transistor (T1) of a first conductivity type having a first main current path connected between the first supply terminal (2) and the first bus terminal (6) and having a first control electrode, a second transistor (T2) of a second conductivity type opposite to the first conductivity type having a second main current path connected between the second supply terminal (4) and the second bus terminal (12) and having a second control electrode, and drive means (18) for driving the first control electrode and the second control electrode, characterized in that the drive means (18) comprise; a common node (20), a third transistor (T3) of the first conductivity type having a third main current path connected between the first supply terminal (2) and the common node (20) and having a third control electrode coupled to the first control electrode, a fourth transistor (T4) of the second conductivity type having a fourth main current path connected between the second supply terminal (4) and the common node (20) and having a fourth control electrode coupled to the second control electrode, a first control voltage source (22) connected between the third control electrode and the common node (20), and a second control voltage source (24) connected between the fourth control electrode and the common node (20). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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Specification