Current driver suitable for use in a shared bus environment
View Patent ↗A transceiver suitable for interfacing a logic device to a shared bus includes a transmit node that receives an input signal from the logic device and an I/O node, that is coupled to the shared bus. The transceiver may be designed for use with a shared-bus, single master, multiple slave architecture, e.g., a Local Interconnect Network (LIN). In a LIN compliant implementation, the transceiver may be suitable for use in at least some types of automobiles and other motorized vehicles. Control logic coupled to the transmit node may assert a current driver enable signal in response to detecting an assertion of the input signal. A current driver of the transceiver is configured to draw a time varying driver current from the shared bus node after detecting an assertion of the current driver enable signal. The driver current may cause a sinusoidal transition of the shared bus voltage.
1. A transceiver suitable for interfacing a logic device to a shared bus, the transceiver comprising:
a transmit node suitable for receiving an input signal from the logic device;
a shared bus node suitable for connecting to the shared bus;
control logic coupled to the transmit node and operable to assert a current driver enable signal in response to detecting an assertion of the input signal; and
a current driver operable to draw a time varying driver current from the shared bus node in response to detecting an assertion of the current driver enable signal, the driver current producing a wave shaped transition of the shared bus voltage, wherein the wave shaped transition approximates at least a portion of a sinusoidal signal;
wherein the driver current includes a resistive component approximating a current attributable to a characteristic resistance of the shared bus and a capacitive component approximating a current attributable to a characteristic capacitance of the shared bus; and
wherein the current driver includes a resistive block operable to draw the resistive component of the driver current and a capacitive block operable to draw the capacitive component of the driver current.
2. The transceiver of claim 1 , wherein:
the resistive block and the capacitive block each include a plurality of current mirrors arranged in parallel, at least some of the current mirrors including a reference transistor and an analog biased transistors configured to draw a reference current through analog biased transistor current terminals and a switching transistor having a control terminal and switching transistor current terminals, the switching transistor current terminals arranged in series with the analog biased transistor current terminals; and
the control logic is operable to assert the current mirror control terminals according to a prescribed timing to simulate the resistive component with the current mirrors of the resistive block and to simulate the capacitive component with the current mirrors in the capacitive block.
3. The transceiver of claim 2 , wherein the control logic is operable to:
assert the control terminals of the resistive block sequentially from a beginning of the transition to the end of the transition; and
assert the control terminals of the capacitive block sequentially from a beginning of the transition to approximately the middle of the transition and to de-assert the controls pins sequentially from approximately the middle of the transition to the end of the transition.
4. The transceiver of claim 2 , wherein sizes of the analog biased transistors vary to produce varying output currents in at least some of the current mirrors.
5. The transceiver of claim 1 , further comprising a third block operable to draw driver current when a magnitude of the shared bus voltage drops below a predetermined threshold.
6. The transceiver of claim 5 , wherein the third block comprises a plurality of transistor switches arranged with their current terminals in parallel, wherein each of the transistor switches is coupled to the LIN node and further wherein the control logic is operable to assert control terminals of the transistor switches in a prescribed manner.
7. A transceiver suitable for interfacing a logic device to a shared bus, the transceiver comprising:
a transmit node suitable for receiving an input signal from the logic device;
a shared bus node suitable for connecting to the shared bus;
control logic coupled to the transmit node and operable to assert a current driver enable signal in response to detecting an assertion of the input signal; and
a current driver operable to draw a time varying driver current from the shared bus node in response to detecting an assertion of the current driver enable signal, the driver current producing a wave shaped transition of the shared bus voltage, wherein the wave shaped transition approximates at least a portion of a sinusoidal signal;
a bias module operable to provide a bias signal to the current driver wherein the bias signal determines, at least in part, a magnitude of the driver current;
a slew time module operable to generate at least one slew signal indicative of a slew time of the transition; and
convergence logic operable to signal the bias module to adjust the bias signal when the slew time differs from a specified value or range of values.
8. The transceiver of claim 7 , wherein the transceiver is operable for use with a shared bus having a single master, multiple slave architecture.
9. The transceiver of claim 7 , where the shared bus is a Local Interconnect Network (LIN) compliant transceiver.
10. A current driver suitable for use in a transceiver coupled to a shared bus having a characteristic impedance including a characteristic resistance and a characteristic capacitance, the current driver being coupled to an I/O node suitable for connecting to the shared bus, the current driver being operable to draw a driver current from the I/O node to produce a transition of the shared bus voltage, wherein the transition approximates a portion of a sinusoidal signal, the current driver comprising:
a resistive block operable to draw a resistive component of the driver current, wherein the resistive component approximates a current attributable to the characteristic resistance were the sinusoidal signal applied to the shared bus; and
a capacitive block operable to draw a capacitive component of the driver current, wherein the resistive component approximates a current attributable to the characteristic capacitance were the sinusoidal signal applied to the shared bus.
11. The current driver of claim 10 , wherein at least one of the resistive block and the capacitive block comprises a plurality of individually controllable current sources arranged in parallel wherein a current terminal of the current sources is coupled to the I/O node.
12. The current driver of claim 11 , wherein the current sources comprise current mirrors including a reference transistor, analog biased transistors and switching transistors.
13. The current driver of claim 10 , further comprising a third block operable to draw a third component of the driver current.
14. The current driver of claim 13 , wherein the third component is substantial relative to a sum of the resistive and capacitive components when a magnitude of the shared bus voltage is less than a predetermined threshold.
15. The current driver of claim 14 , wherein the third block comprises a plurality of transistor switches arranged in parallel.