Reduced frequency backwards clock for isolated sigma-delta modulators

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/811,361, filed Apr. 12, 2013, and titled “REDUCED FREQUENCY BACKWARDS CLOCK FOR ISOLATED SIGMA-DELTA MODULATORS,” which is herein incorporated by reference in its entirety.

BACKGROUND

Industrial and process control systems include various types of control equipment used in industrial production, such as supervisory control and data acquisition (SCADA) systems, distributed control systems (DC S), and other control equipment using, for example, programmable logic controllers (PLC). These control systems are typically used in industries including electrical, water, oil, gas, and data. Using information collected from remote stations in the field, automated and/or operator-driven supervisory commands can be transmitted to field control devices. These field devices control local operations, such as the speed of an electrical motor. Industrial control systems/process control systems may require electrical isolation between power transmission and control equipment. For example, optical equipment can be used for signal transmission to electrically isolate devices, prevent ground loops, and so forth.

SUMMARY

A system includes a divider on a first side of electrically isolated circuitry for receiving a clock signal having a characteristic frequency and dividing the clock signal by a characteristic value. The system also includes an optical link coupled with the divider for receiving the divided clock signal and transmitting the divided clock signal from the first side of the electrically isolated circuitry to a second side of the electrically isolated circuitry. The system further includes a phase-locked loop on the second side of the electrically isolated circuitry. The phase-locked loop is coupled with the optical link and configured to receive the divided clock signal from the optical link and generate a second signal at a multiple of a characteristic frequency of the divided clock signal so that the second signal comprises the characteristic frequency of the clock signal received by the divider circuitry.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

DRAWINGS

The Detailed Description is described with reference to the accompanying figures. The use of the same reference numbers in different instances in the description and the figures may indicate similar or identical items.

FIG. 1 is a diagrammatic illustration of a system that provides electrical isolation using optical links.

FIG. 2 is a diagrammatic illustration of a system that provides electrical isolation using a high speed optical link and a low speed optical link in accordance with an example embodiment of the present disclosure.

FIG. 3 is a diagrammatic illustration of a chip package that provides electrical isolation using a high speed optical link and a low speed optical link in accordance with an example embodiment of the present disclosure.

DETAILED DESCRIPTION

Referring generally to FIG. 1, a system 50 providing optical coupling is described. The system 50 includes two high speed, unidirectional optical links 52 and 54 that provide bidirectional communication (e.g., between a high voltage side 56 and a low voltage side 58). On the high voltage side 56, current-sense functionality is provided using a sigma-delta modulator and an associated oscillator 60. Synchronization of the oscillator 60 is achieved via a “backwards” optical link 54 that furnishes a clock signal from the low voltage side 58 to the high voltage side 56. In the configuration shown in FIG. 1, the backwards optical link 54 transmits a high speed clock signal (e.g., a twenty megahertz (20 MHz) clock signal) through the optical-coupler 54. However, a high speed backwards optical link consumes increased power, is more expensive, and has a shorter lifespan (e.g., with respect to a lower speed optical link).

Referring generally to FIGS. 2 and 3, a system 100 providing optical coupling is described. The system 100 includes a high speed, unidirectional optical link 102 (e.g., a twenty megahertz (20 MHz) optical link) for transmitting signals from a high voltage side 104 of the system 100 to a low voltage side 106 of the system 100. The system 100 also includes a low speed, low power unidirectional optical link 108 (e.g., a ten kilohertz (10 kHz) optical link) for transmitting signals from the low voltage side 106 to the high voltage side 104. In embodiments of the disclosure, one or more of the optical links 102 and 108 includes a light emitting diode (LED). The high voltage side 104 of the system 100 is configured to couple with, for example, a motor, and the low voltage side 106 of the system 100 is configured to couple with, for example, a controller (e.g., for controlling the speed of the motor). In some embodiments, the high voltage side 104 is coupled with a floating ground. On the high voltage side 104, current-sense functionality is provided using a sigma-delta modulator 110 and an associated oscillator 112. Synchronization of the oscillator 112 is achieved via the low speed optical link 108 that furnishes a clock signal from the low voltage side 106 to the high voltage side 104.

The system 100 described in FIG. 2 implements a reduced backwards clock frequency for the isolated sigma-delta modulator 110 (e.g., with respect to the system 50 described with reference to FIG. 1). In this embodiment, a clock multiplier is coupled with the sigma-delta modulator 110 and a divided clock signal (e.g., a master clock signal) is transmitted to the high voltage side 104 of the system 100 along a low speed, backwards clock path 114 via the low speed optical link 108. The low speed optical link 108 reduces cost and power requirements for the system 100, while increasing the reliability and/or lifespan of the system 100. As shown, an external master clock signal on the low voltage side 106 of the optical isolator is divided by a characteristic value, N. In some embodiments, N is equal to at least approximately 2¹¹ (2048) and reduces the reverse link speed to at least approximately ten kilohertz (10 kHz). The divided clock signal is transmitted through the low speed optical link 108, and a clock multiplier (e.g., a high-precision clock multiplier) synchronizes the sigma-delta modulator 110 with the external master clock. This configuration allows for synchronized measurement of shunt current with the master clock from the low voltage side 106 of the system 100.

Referring now to FIG. 3, in some embodiments the sigma-delta modulator 110, the oscillator 112, and phase detector and filter circuitry 116 (e.g., implementing a phase-locked loop (PLL)) are provided on a first integrated circuit (IC) chip 118; the LED drivers, LEDs, and optical receiver circuitry of the optical links 102 and 108 are provided on a second optical isolator IC chip 120; and the divider, clock and data recovery circuitry are provided on a third IC chip 122. The first, second, and third IC chips 118, 120, and 122 are included in a single chip package 124. In this configuration, the alignment of LED transmission and receiver circuitry may not be as critical for the low speed optical link 108 because of its reduced power requirements. For example, when two high speed optical links are provided on a common IC chip as shown in FIG. 1, the alignment of the transmission and receiver circuitry for both optical links 52 and 54 is critical, and often results in a chip that has increased power requirements (e.g., due to a sub-optimal alignment of the optical components on the chip). However, this configuration is provided by way of example only and is not meant to limit the present disclosure. Thus, in other configurations, the circuitry described is included on a single IC chip, is arranged differently on multiple IC chips, and so forth.

In embodiments of the disclosure, systems 100 described herein are used in one or more applications including, but not necessarily limited to: a programmable logic controller (PLC), a motor controller, a medical device, a photovoltaic (PV) solar device, a direct current-to-direct current (DC-to-DC) power inverter, and so forth. For example, the system 100 described with reference to FIGS. 2 and 3 can be implemented in industrial (e.g., industrial control) and/or automation markets. In some embodiments, the system 100 is implemented in a reduced power, optically isolated analog-to-digital (A/D) converter.

Although the subject matter has been described in language specific to structural features and/or process operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.