Driver circuit with emi immunity

Abstract

A driver circuit suitable for outputting a signal onto an output line affected by conducted EMI, has a slope control circuit and an output circuit, (op-amp, Mo, M 13 to M 21 ). It can be used for driving a LIN network. The slope control circuit outputs a slope controlled version of the input signal to the output circuit, which (M 6 ,M 7 ) is arranged to reduce an amount of conducted EMI induced DC shift in the output circuit. This can involve clipping a feedback signal, and regulating an output stage of the op-amp to prevent the DC shift. Having a separate output circuit can help shield the slope control circuit from the EMI on the output line.

1 . A driver circuit suitable for outputting a signal onto a line affected by conducted EMI, the driver circuit comprising:
 a slope control circuit receiving an input signal and outputting a first slope controlled signal that has a slope controlled rising edge responsive to a particular transition of the input signal and a slope controlled falling edge responsive to another transition of the input signal that is opposite the particular transition of the input signal;   an operational amplifier configured to receive the output of the slope control circuit and responsively output a second slope controlled signal that has a slope controlled rising edge responsive to a particular transition of the first slope controlled signal, the second slope controlled signal also having a slope controlled falling edge responsive to another transition of the first sloped controlled signal that is opposite the particular transition of the first slope controlled signal; and   an output transistor, receiving the output of the operational amplifier wherein the output transistor is arranged to output a third slope controlled signal to the line.   
     
     
         2 . The driver circuit in accordance with  claim 1 , wherein the slope controlled rise edge of the first slope controlled signal has a rate of change that falls within predetermined limits. 
     
     
         3 . The driver circuit in accordance with  claim 2 , wherein the slope controlled falling edge of the first slope controlled signal has a rate of change that falls within predetermined limits. 
     
     
         4 . The driver circuit in accordance with  claim 1 , wherein a slope controlled rise edge of the third slope controlled signal has a rate of change that falls within predetermined limits. 
     
     
         5 . The driver circuit in accordance with  claim 4 , wherein a slope controlled falling edge of the third slope controlled signal has a rate of change that falls within predetermined limits. 
     
     
         6 . The driver circuit in accordance with  claim 1 , wherein the output of the slope control circuit is received at a first input of the operation amplifier, the driver circuit further comprising:
 a feedback path between the output of the operational amplifier and a second input of the operational amplifier.   
     
     
         7 . The driver circuit in accordance with  claim 6 , wherein the feedback path comprises a clipping circuit for reducing an amount of the conducted EMI provided over the feedback path from the output of the operational amplifier to the second input of the operational amplifier. 
     
     
         8 . The driver circuit in accordance with  claim 7 , the clipping circuit comprising two transistors of different polarity, both transistors being connected between the feedback path and the supply voltage, the gates of both transistors being coupled to the first input of the operational amplifier. 
     
     
         9 . The driver circuit in accordance with  claim 8 , further comprising a buffer circuit, the input of the buffer circuit being coupled to the line and the output of the buffer circuit being coupled to the second input of the operational amplifier. 
     
     
         10 . The driver circuit in accordance with  claim 1 , the operational amplifier comprising an output stage having an internal negative feedback circuit arranged to reduce the EMI induced DC level shift. 
     
     
         11 . The driver circuit in accordance with  claim 1  and arranged to be suitable for driving a LIN network. 
     
     
         12 . A system for generating an input signal, and having one or more driver circuits, each of the one or more driver circuits being suitable for outputting a signal onto a line affected by conducted EMI, each of the one or more driver circuits comprising:
 a slope control circuit receiving an input signal and outputting a first slope controlled signal that has a slope controlled rising edge responsive to a particular transition of the input signal and a slope controlled falling edge responsive to another transition of the input signal that is opposite the particular transition of the input signal;   an operational amplifier configured to receive the output of the slope control circuit and responsively output a second slope controlled signal that has a slope controlled rising edge responsive to a particular transition of the first slope controlled signal, the second slope controlled signal also having a slope controlled falling edge responsive to another transition of the first sloped controlled signal that is opposite the particular transition of the first slope controlled signal; and   an output transistor, receiving the output of the operational amplifier wherein the output transistor is arranged to output a third slope controlled signal to the line.   
     
     
         13 . The system in accordance with  claim 12 , wherein for at least one of the one or more driver circuit, a slope controlled rising edge of the third slope controlled signal has a rate of change that falls within predetermined limits. 
     
     
         14 . The system in accordance with  claim 12 , wherein for at least one of the one or more driver circuit, a slope controlled falling edge of the third slope controlled signal has a rate of change that falls within predetermined limits. 
     
     
         15 . The system in accordance with  claim 12 , wherein for each of the one or more driver circuit, a slope controlled rising edge of the third slope controlled signal has a rate of change that falls within predetermined limits, and a slope controlled falling edge of the third slope controlled signal has a rate of change that falls within predetermined limits. 
     
     
         16 . A network comprising:
 a line affected by conducted EMI;   two or more systems coupled to the line, each of the systems comprising one or more driver circuits, each driver circuit of each system being suitable for outputting a signal onto the line, each of the one or more driver circuits comprising:   a slope control circuit receiving an input signal and outputting a first slope controlled signal that has a slope controlled rising edge responsive to a particular transition of the input signal and a slope controlled falling edge responsive to another transition of the input signal that is opposite the particular transition of the input signal;   an operational amplifier configured to receive the output of the slope control circuit and responsively output a second slope controlled signal that has a slope controlled rising edge responsive to a particular transition of the first slope controlled signal, the second slope controlled signal also having a slope controlled falling edge responsive to another transition of the first sloped controlled signal that is opposite the particular transition of the first slope controlled signal; and   an output transistor, receiving the output of the operational amplifier wherein the output transistor is arranged to output a third slope controlled signal to the line.   
     
     
         17 . A method of using a driver circuit to drive a line according to an input signal, the line being affected by conducted EMI, the method comprising:
 controlling transitions of the input signal to a predetermined slope within predetermined limits in a slope control circuit;   amplifying the signal having controlled transitions in an operational amplifier; and   sending the amplified signal having controlled transitions to an output stage for driving the line, the amplified signal having controlled transitions has a slope controlled rising edge and a slope controlled falling edge so that the effect of the conducted EMI from the line on the slope output is limited.   
     
     
         18 . The method in accordance with  claim 17 , further comprising:
 feeding back the driving signal, delivered by the output stage to an input of the operational amplifier.   
     
     
         19 . The method in accordance with  claim 18 , further comprising:
 clipping the feedback signal in order to reduce an amount of the conducted EMI in the feedback to the amplifier.   
     
     
         20 . The method in accordance with  claim 17 , wherein transitions of the input signal are controlled so that the rate of change for both the rising edge and the falling edge of the input signal are within predetermined limits.