Multiple die industrial process control transmitter

• US 6,480,131 B1
• Filed: 08/10/2000
• Issued: 11/12/2002
• Est. Priority Date: 08/10/2000
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Westfield, Brian L., Gaboury, Michael J., Tyson, David G., Roper, Weston R.
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Nguyen, John
• Application Number:
  US09/636,152
• Time in Patent Office: 824 Days
• Field of Search: 341/155, 341/156, 341/110, 341/137, 341/116, 341/120, 341/143, 341/119, 341/115, 341/118, 341/114, 341/176
• US Class Current: 341/155
• CPC Class Codes: G05B 19/0423 Input/output
• CPC Class Codes: G05B 19/4142 characterised by the use of a microprocessor G05B19/4141 takes precedence
• CPC Class Codes: G05B 2219/31121 Fielddevice, field controller, interface connected to fieldbus
• CPC Class Codes: G05B 2219/31126 Transmitter coupled to fieldbus and to sensor, a-d conversion
• CPC Class Codes: G05B 2219/33197 Current loop 4-20-mA milliampere
• CPC Class Codes: G05B 2219/34309 Dual power supply, for digital circuit and for analog signals

Abstract

A two-wire industrial process control transmitter includes a sensor, at least two integrated circuits, and a level shift circuit. The first integrated circuit contains the analog measurement circuit that includes a sensor detection circuit and the analog portion of a digital-to-analog convertor. The second integrated circuit contains the digital system circuit that includes a modem and the digital portion of the analog-to-digital convertor. The first and second ICs may be powered at different voltage levels to maximize the power of the analog circuit and improve resolution. Alternatively, the ICs may be powered at the same voltage level, but the digital circuits are divided among several stacked dies to minimize the voltage for each digital circuit. In either case, the level shifting circuit shifts the voltage level between the analog and digital circuits.

Claims

1. An industrial process control transmitter adapted to be coupled to a two-wire loop, comprising:

a sensor;

a first integrated circuit chip containing;

a first power rail energized from the two-wire loop to provide a first voltage level, and

an analog measurement circuit coupled to the sensor and powered by the first voltage level, the analog measurement circuit includes a sensor detection circuit and analog portions of an analog-to-digital convertor to derive a first compensated analog signal representative of a sensed parameter;

a second integrated circuit chip, separate from the first integrated circuit chip containing;

a digital system circuit that includes digital portions of the analog-to-digital convertor, the digital portions of the analog-to-digital convertor responsive to a second compensated analog signal, and

a second power rail energized from the two-wire loop providing a second voltage level lower than the first level, the second power rail powering at least a portion of the digital system circuit; and

a level shifting circuit shifting a voltage level of the first compensated analog signal to the second voltage level to derive a second compensated analog signal.

2. The transmitter of claim 1, wherein the digital system circuit on the second integrated circuit chip includes a modem to transmit a signal representative of the digital representation.

3. The transmitter of claim 1, wherein the transmitter is of the 4-20 mA class, and the analog measurement circuit and the digital system circuit together draw no more than 18 mW and no more than 3 mA from the loop, the transmitter including

a DC-to-DC converter energizing the second power rail at a second voltage level no more than two diode drops and energizing the first power rail at a first voltage level so that the power consumed by the analog measurement circuit is no more than 18 mW minus the power consumed by the first integrated circuit and the current drawn by the analog measurement circuit is no more than 3 mA minus the current drawn by the digital system circuit.

4. The transmitter of claim 3, wherein the digital system circuit on the second integrated circuit chip includes a modem to transmit a signal representative of the digital representation.

5. The transmitter of claim 1, including a common power rail coupled to the first and second integrated circuit chips and energized by the two-wire loop to provide a common voltage level, the second integrated circuit chip including:

first and second dies each forming respective portions of the digital system circuit,

a multichip module stacking the first and second dies,

the first power rail coupled to the first die to supply the first voltage level to the portion of the digital system circuit on the first die,

the common power rail coupled to the second die to supply the common voltage level to the portion of the digital system circuit on the second die, and

an interface coupled to the first and second dies, the interface including the second power rail to supply the second voltage level to the portions of the digital system circuit on the first and second dies, the second voltage level being between the first and common voltage levels,

whereby the portion of the digital circuit on the first die is powered by a voltage difference between the first and second voltage levels and the portion of the digital circuit on the second die is powered by a voltage difference between the second and common voltage levels.

6. The transmitter of claim 5, including a modem on one of the dies to transmit a signal representative of the digital representation.

7. The transmitter of claim 6, including a second level shifting circuit for shifting a voltage level of data signals between the first and second dies.

8. The transmitter of claim 5, including a second level shifting circuit for shifting a voltage level of data signals between the first and second dies.

9. The transmitter of claim 5, wherein the transmitter is of the 4-20 mA class, and the analog measurement circuit and the digital system circuit together draw no more than 18 mW and no more than 3 mA from the loop, the transmitter including

a DC-to-DC converter on the first chip and connected to the first and second power rails to energize the second power rail at the second voltage level no more than two diode drops below the first voltage level so that the power consumed by the analog measurement circuit is no more than 18 mW minus the power consumed by the digital system circuit and the current drawn by the analog measurement circuit is no more than 3 mA minus the current drawn by the first and second dies.

10. The transmitter of claim 9, including a modem on one of the dies to transmit a signal representative of the digital representation.

11. The transmitter of claim 10, including a second level shifting circuit for shifting a voltage level of data signals between the first and second dies.

12. The transmitter of claim 9, including a second level shifting circuit for shifting a voltage level of data signals between the first and second dies.

17. The transmitter of claim 1, wherein the level shifting circuit is on the first chip.

13. An industrial process control transmitter adapted to be coupled to a two-wire loop, comprising:

a sensor;

a first integrated circuit on a first chip comprising an analog measurement circuit coupled to the sensor, the analog measurement circuit includes a sensor detection circuit and analog portions of an analog-to-digital convertor to derive a first compensated analog signal representative of a value of a sensed parameter;

a second integrated circuit comprising;

a first die that includes at least digital portions of the analog-to-digital convertor responsive to a second compensated analog signal,

a second die that includes at least a modem responsive to the digital portions of the analog-to-digital converter to transmit a signal representative of the sensed parameter,

a multichip module stacking the first and second dies, and

an interface power rail between the first and second dies;

a first power rail energized by the two-wire loop to provide a first voltage level to the first die and to the first integrated circuit;

a second power rail energized by the two-wire loop to provide a common voltage level to the second die and to the first integrated circuit;

a first level shifting circuit for shifting a voltage level of the first compensated analog signal to derive the second compensated analog signal, and

a second level shifting circuit for shifting a voltage level of data signals between the first and second dies.

14. The transmitter of claim 13, wherein the interface power rail supplies a second voltage level between the first and common voltage levels, whereby the first die is powered by a voltage difference between the first and second voltage levels and the second die is powered by a voltage difference between the second and common voltage levels.

15. The transmitter of claim 14, wherein transmitter is of the 4-20 mA class, and the analog measurement circuit and the digital system circuit together draw no more than 18 mW and no more than 3 mA from the loop.

16. The transmitter of claim 13, wherein transmitter is of the 4-20 mA class, and the analog measurement circuit and the digital system circuit together draw no more than 18 mW and no more than 3 mA from the loop.