Compensation for ground voltage variation on a communication bus
AssigneeDelco Electronics Corporation
InventorDavid D. Moller
Life of this patent
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Abstract
A serial communication bus for a motor vehicle subject to different ground voltages on the common line and a transmitting module has a compensation circuit to prevent mismatches which distort pulse current waveforms and cause radiated emissions. When line ground voltage is higher than the transmitter voltage an integrator is used to simulate the line ground voltage and apply that to the transmitter ground. The integrator has a small current source and a very large current sink to follow the line ground potential. The transmitter output is disabled between pulses to avoid increasing the line ground voltage. When line ground voltage is lower than the transmitter voltage, the transmitter is enabled between pulses to feed current to the line to increase its potential.
Claims14
In a serial communication system having a common line carrying data pulses among a plurality of communication modules, wherein the ground voltage of a module may be different from the common line ground voltage, a transmitting module comprising:
- waveshaping means having a module ground voltage, and being operative to generate data pulses shaped to minimize electromagnetic emissions;
- an output circuit for coupling data pulses from the waveshaping means to the common line;
- and
- compensation means for equalizing the module ground voltage and the common line ground voltage by applying common line ground voltage to the module ground voltage, and by feeding current to the common line between successive data pulses of said waveshaping means when the common line ground voltage is low relative to the module ground voltage.
In a serial communication system having a common line carrying data pulses among a plurality of communication modules, wherein the ground voltage of a module may be different from the common line ground voltage, and wherein a transmitting module includes a waveshaping circuit having a module ground voltage, and being operative to generate data pulses and an output circuit for coupling pulses from the waveshaping means to the common line, a method of equalizing the module ground voltage and the common line ground voltage comprising the steps of:
- producing a simulated ground voltage equivalent to the common line ground voltage;
- applying the simulated ground voltage to the module ground voltage;
- and
- feeding current to the common line to increase the common line ground voltage when the simulated ground voltage is below a set reference value.
Dependencies are inferred from the claim text.