Pseudo-sinusoidal waveform generator for HART communication
A communication system includes a first system input adapted to be coupled to a DC transient current transitioning between a starting level and a target level on a pseudo-sinusoidal path and incudes a second system input adapted to be coupled to a HART signal. The system includes an adder circuit having an output, a first adder input coupled to the first system input and a second adder input coupled to the second system input. The adder circuit provides a superimposed signal comprising the HART signal and the DC transient current.
1. A Highway Addressable Remote Transducer (HART) communication system comprising:
a first system input adapted to be coupled to a DC transient current transitioning between a starting level and a target level on a pseudo-sinusoidal path;
a second system input adapted to be coupled to a HART signal;
an adder circuit having an output, a first adder input coupled to the first system input and a second adder input coupled to the second system input.
2. The HART communication system of claim 1 , wherein the adder circuit is configured to provide a superimposed signal comprising the HART signal and the DC transient current.
3. The HART communication system of claim 1 , further comprising:
a waveform generator configured to provide a digital-to-analog converter (DAC) code; and
a digital-to-current converter configured to receive the DAC code.
4. The communication system of claim 1 , further comprising:
an analog filter having an output and an input coupled to the output of the adder circuit; and
a digital filter having an output and an input coupled to the output of the adder circuit.
5. The HART communication system of claim 4 , wherein the analog filter is a low-pass filter configured to isolate an analog signaling spectrum.
6. The communication system of claim 4 , wherein the digital filter is a band-pass filter configured to isolate a digital signaling spectrum.
7. A communication system, comprising:
a waveform generator configured to provide a digital-to-analog converter (DAC) code;
a digital-to-current converter configured to receive the DAC code and to provide a DC transient current transitioning between a starting level and a target level on a pseudo-sinusoidal path;
an adder circuit having an output, a first input coupled to the DC transient signal and a second input adapted to be coupled to a Highway Addressable Remote Transducer (HART) signal.
8. The communication system of claim 7 , wherein the adder circuit is configured to add the DC transient current and the HART signal and provide a superimposed signal having an analog signaling spectrum and a digital signaling spectrum of a HART communication protocol.
9. The communication system of claim 7 , further comprising:
an analog filter having an output and an input coupled to the output of the adder circuit; and
a digital filter having an output and an input coupled to the output of the adder circuit.
10. The HART communication system of claim 9 , wherein the analog filter is a low-pass filter configured to isolate an analog signaling spectrum.
11. The communication system of claim 9 , wherein the digital filter is a band-pass filter configured to isolate a digital signaling spectrum.
12. The communication system of claim 7 , wherein a first starting level is 4 mA and a first target level is 20 mA, and wherein a second starting level is 20 mA and a second target level is 4 mA.
13. A communication system, comprising:
a step selector having a first input configured to receive a positive slew value, a second input configured to receive a negative slew value, and a third input configured to receive a comparison signal, the step selector configured to provide a slew step responsive to the comparison signal;
a first adder circuit having a first input configured to receive the slew step and a second input, the first adder circuit configured to provide a current slew rate at an output;
a memory device having an input coupled to the output of the first adder and an output coupled to the second input of the first adder;
a second adder circuit having a first input configured to receive the current slew rate and a second input configured to receive a digital-to-analog converter (DAC) code, the second adder circuit configured to provide a next DAC code raw signal at an output;
a latch having an input configured to receive the next DAC code raw signal and a rising-edge clock input configured to receive a clock signal, the latch configured to provide the DAC code;
a comparison circuit having a first input configured to receive the DAC code and a second input configured to receive a transition value, the comparison circuit configured to provide the comparison signal;
a digital-to-current converter configured to receive the DAC code and to provide a DC transient current transitioning between a starting level and a target level on a pseudo-sinusoidal path; and
a third adder circuit having an output, a first input coupled to the DC transient signal and a second input adapted to be coupled to a Highway Addressable Remote Transducer (HART) signal.
14. A method of communication, comprising:
providing a DC transient current rising from a first starting level to a mid point between the first starting level and a first target level at an accelerating slew rate and rising from the mid point to the first target level at a decelerating slew rate, the DC transient current falling from a second starting level to the mid point at the accelerating slew rate and falling from the mid point to a second target level at the decelerating slew rate;
providing a HART signal;
adding the DC transient current and the HART signal and providing a superimposed signal having an analog signaling spectrum and a digital signaling spectrum of HART communication protocol;
transmitting the superimposed signal over a connector; and
receiving the superimposed signal and isolating the analog signaling spectrum and the digital signaling spectrum.