ADAPTIVE COMMON MODE DIMMER

Abstract

An adaptive common-mode dimmer (104a; 108a) having a first low quiescent current operating mode and a second high quiescent current operating mode; wherein: the common mode dimmer (104a; 108a) is configured to: coupling to a two-wire transmission line (110); and Maintaining a common mode voltage (Vcm) thereon at a desired common mode reference voltage (Vmid); the two-wire transmission line (110) is configured to transmit differential signals; the common-mode dimmer (104a; 108a) is configured to operate in the first mode when the common-mode voltage (Vcm) on the two-wire transmission line (110) is between a high common-mode reference voltage (Vhi) and a low common-mode reference voltage (Vlo); and the common mode dimmer (104a; 108a) is configured to otherwise operate in the second mode.

Description

[0001] The present invention relates to power technology and, more particularly, to an adaptive common mode dimmer.

[0002] Common-mode currents (CM currents) can be caused by a bulk current injection (BCI) event through capacitive coupling of a noise source, electromagnetic interference (EMI), and / or magnetic coupling. CM currents can cause cables in electrical systems to act as unintentional radiators / receivers. CM radiation has been shown to be proportional to cable length and signal frequency. Reducing CM radiation generally requires minimizing the CM current or the CM signal frequency. One way to reduce CM current is to use CM dimmer circuits coupled to differential drivers and receivers that communicate over a two-wire differential signal transmission line. This requires differential driver circuits in the CM dimmer circuit that have sufficient drive / sink current to handle BCI events.However, to ensure sufficient driver / sink current capacity, the CM dimmer's differential driver circuits must operate at a high quiescent current. This represents a significant power consumption for the overall system.

[0003] From the US patent application US 2008 / 0024178 A1, transmission line drivers and serial data interface transmission devices with the same are known.

[0004] Therefore, there is a need for a CM dimmer circuit with lower power consumption during normal operation when no BCI events occur, yet capable of handling high-current CM-BCI events when they do occur. These and other objects are achieved by an adaptive common-mode dimmer and a system for transmitting signals over a differential transmission line and using adaptive common-mode dimmers according to the independent claims.

[0005] According to one embodiment, an adaptive common-mode dimmer may comprise: a common-mode dimmer having a first low quiescent current operating mode and a second higher quiescent current operating mode, and the common-mode dimmer may be configured to couple to a two-wire transmission line and maintain a common-mode voltage thereon with a desired common-mode reference voltage, wherein the two-wire transmission line may carry differential signals; wherein the common-mode dimmer may be in the first mode when the common-mode voltage on the two-wire transmission line may be between a high common-mode reference voltage and a low common-mode reference voltage, and may be in the second mode otherwise.

[0006] According to another embodiment, the high common-mode reference voltage is less than a power supply voltage; the desired common-mode reference voltage is less than the high common-mode reference voltage; and the low common-mode reference voltage is less than the desired common-mode reference voltage and greater than a ground or power supply common-mode voltage. According to another embodiment, the desired common-mode reference voltage may be about half of a power supply voltage. The tolerances for half of a supply voltage may be, for example, within 1%, 5%, or 10%. According to another embodiment, a bulk current injection (BCI) event may cause the common-mode voltage to be above the high common-mode reference voltage or below the low common-mode reference voltage, with the common-mode dimmer in the second mode.According to another embodiment, the common mode dimmer may cause the common mode voltage to return between the high and low common mode reference voltages before changing from the second mode to the first mode.

[0007] According to another embodiment, if the common-mode voltage may be above the desired common-mode reference voltage, the common-mode dimmer may shunt current from the two-wire transmission line to a ground or a common power supply reference line. According to another embodiment, if the common-mode voltage may be below the desired common-mode reference voltage, the common-mode dimmer may supply current from the power supply voltage to the two-wire transmission line. According to another embodiment, the BCI event may cause at least 200 milliamperes of common-mode current on the two-wire transmission line, and the common-mode dimmer may be in the second mode when the common-mode voltage may be greater than the high common-mode reference voltage or less than the low common-mode reference voltage.

[0008] According to another embodiment, a method for reducing the common-mode voltage on a differential signal transmission line using an adaptive common-mode dimmer having low and high quiescent current modes may comprise the steps of: providing a common-mode dimmer having a first low quiescent current mode and a second higher quiescent current mode; coupling the common-mode dimmer to a two-wire transmission line to maintain a common-mode voltage thereon at a desired common-mode reference voltage, the two-wire transmission line carrying differential signals; operating the common-mode dimmer in the first mode when the common-mode voltage on the two-wire transmission line may be between a high common-mode reference voltage and a low common-mode reference voltage;and operating the common-mode dimmer in the second mode when the common-mode voltage on the two-wire transmission line can be greater than the high common-mode reference voltage or lower than the low common-mode reference voltage;

[0009] According to another embodiment of the method, the high common-mode reference voltage may be less than a power supply voltage; the desired common-mode reference voltage may be less than the high common-mode reference voltage; and the low common-mode reference voltage may be less than the desired common-mode reference voltage and greater than a ground or power supply common-mode voltage. According to another embodiment of the method, the desired common-mode reference voltage may be about half the supply voltage. According to another embodiment of the method, it may include the step of causing the common-mode dimmer to be in the second mode during a current injection (BCI) event when the common-mode voltage may be above the high common-mode reference voltage or below the low common-mode reference voltage.According to a further embodiment of the method, it may comprise the step of resetting to a common-mode voltage lying between the high and low common-mode reference voltages when the common-mode dimmer may be in the second mode. According to a further embodiment of the method, it may comprise the step of shunting current from the two-wire transmission line to ground or the common power supply reference line when the common-mode voltage may be above the desired common-mode reference voltage. According to a further embodiment of the method, it may comprise the step of supplying current to the two-wire transmission line from a power supply voltage when the common-mode voltage may be below the desired common-mode reference voltage.

[0010] According to yet another embodiment, a system for transmitting signals over a differential transmission line and having adaptive common-mode dimmers with low and high quiescent current modes of operation may comprise: a differential signal transmitter having a first adaptive common-mode dimmer coupled thereto; a differential signal receiver having a second adaptive common-mode dimmer coupled thereto; and a differential signal transmission line coupling the differential signal transmitter and the differential signal receiver; wherein the first and second adaptive common-mode dimmers each have a first low quiescent current mode of operation and a second higher quiescent current mode of operation;wherein the first and second adaptive common-mode dimmers are operable in the first mode when a common-mode voltage on the two-wire transmission line is between a high common-mode reference voltage and a low common-mode reference voltage, and are operable in the second mode otherwise;

[0011] According to yet another embodiment, an adaptive common-mode dimmer may comprise: a first set of current drivers coupled between a power supply voltage and a two-wire transmission line; a second set of current drivers coupled between a ground or common power supply reference line and the two-wire transmission line; first and second voltage comparators having outputs coupled to and controlling the first and second sets of current drivers, first inputs connected to the two-wire transmission line, and second inputs connected to a first reference voltage, wherein the first reference voltage may be less than the power supply voltage and greater than the ground or common power supply voltage reference line;wherein, when a common-mode voltage on the two-wire transmission line may be greater than the first reference voltage, the second set of current drivers will consume more current than the first set of current drivers, and when the common-mode voltage on the two-wire transmission line may be less than the first reference voltage, the first set of current drivers will source more current than the second set of current drivers sink; a third voltage comparator having a first input coupled to a second reference voltage, a second input coupled to the two-wire transmission line, and an output coupled to the second set of current drivers to increase their quiescent operating current when the common-mode voltage may be greater than the second reference voltage, wherein the second reference voltage may be greater than the first reference voltage;and a fourth voltage comparator having a first input coupled to a third reference voltage, a second input coupled to the two-wire transmission line, and an output coupled to the first set of current drivers to increase their quiescent operating current when the common-mode voltage may be less than the third reference voltage, wherein the third reference voltage may be less than the first reference voltage;

[0012] According to another embodiment, the first reference voltage may be approximately half the supply voltage. According to another embodiment, a first buffer transistor may be located between the output of the fourth voltage comparator and the first set of current drivers.

[0013] According to a further embodiment, a second buffer transistor may be located between the output of the third voltage comparator and the second set of current drivers.

[0014] A more complete understanding of the present disclosure can be obtained by reference to the following description taken in conjunction with the accompanying drawings in which: Fig. 1 illustrates a schematic block diagram of a differential transmitter and receiver pair, each having common mode dimmers coupled thereto, in accordance with the teachings of this disclosure; Fig. 2 illustrates a schematic diagram of a common mode dimmer according to the teachings of this disclosure; Fig. 3 illustrates a schematic diagram of an adaptive common mode dimmer according to a specific exemplary embodiment of this disclosure; and Fig. 4 illustrates a schematic block diagram of a differential transceiver pair having common mode dimmers coupled to each of them in accordance with the teachings of this disclosure.

[0015] While the present disclosure is susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown in the drawings and will be described in detail herein. It should be understood, however, that the description of specific exemplary embodiments herein is not intended to limit the disclosure to the forms disclosed herein.

[0016] An adaptive mode has been added to a common-mode (CM) dimmer circuit to increase the output current capability only when needed. Without an adaptive mode in the CM dimmer, the output current drivers must operate with a large quiescent current to handle a bulk current injection (BCI) event. Therefore, a CM dimmer without an adaptive mode consumes a significant amount of power even when no BCI event occurs. With the adaptive mode, the CM dimmer can be effectively used to suppress the BCI event, for example, in a transformerless physical layer (PHY) interconnect, while consuming minimal power during normal circuit operation.

[0017] Referring now to the drawings, the details of exemplary embodiments are schematically illustrated. Like elements in the drawings are represented by like numbers, and similar elements are represented by like numbers with a different lowercase suffix.

[0018] In Fig. 1 is a schematic block diagram of a differential transmitter and receiver pair each having common mode dimmers coupled thereto in accordance with the teachings of this disclosure. Fig. Figure 1 shows a simplified typical connection between a transmitter 114 with a differential output and a receiver 116 with a differential input, each coupled to a common-mode (CM) dimming circuit 104a, 108a. The electrical signal connection between the differential transmitter 114 and the differential receiver 116 may be made with a pair of wires forming a transmission line 110, e.g., unshielded twisted pair (UTP) wires or coaxial (shielded) cables.

[0019] The common mode current I BCI(represented by a current source 112) from any external disturbance can be injected onto the transmission line 110 through capacitive coupling, electromagnetic interference, and / or magnetically induced interference. This phenomenon is commonly referred to as "bulk current injection" (BCI). During this BCI event, the common-mode voltage (voltage between wires and ground) of the differentially connected wire pair (OUTP, OUTN, INP, INN) that forms the transmission line 110 increases as the injected CM current I BCI is positive, and decreases when it is negative. The CM dimmer circuits 104a, 108a then conduct currents onto or off the differentially connected pair of wires 110 to counteract the externally induced common-mode current I BCI from a BCI event.

[0020] Referring to Fig. Figure 4 shows a schematic block diagram of a differential transceiver pair, each coupled to a common-mode dimmer according to the teachings of this disclosure. Transceivers 414 and 416 are coupled to and communicate via a differential transmission line 110. The operation of transceivers 414 and 416 is functionally the same as that of the Fig. 1, but can communicate in a half-duplex mode. For a full-duplex communication mode, a second differential transmission line (not shown) can be provided and coupled directly between the receiver 406 and the transmitter 402; however, in this configuration, additional CM dimmers would need to be provided for and coupled to the second differential transmission line.

[0021] In Fig. 2 is a schematic diagram of a common-mode dimmer according to the teachings of this disclosure. Each of the CM dimmer circuits 104a, 108a may include voltage comparators 224, 226; resistors 220, 222, 236, 238; and transistors 228, 230, 232, 234, 240, 242, 244, 246. Additional resistors and capacitors not numbered are not relevant to the discussion herein but have been included for circuit completeness. The resistors and capacitors shown in Fig. The CM dimmer circuit 104a, 108a shown in Figure 2 measures the common-mode voltage, Vcm, of a differential signal pair SIGP, SIGN and adjusts it to be substantially equal to the common-mode voltage reference Vmid (Vmid = V DD / 2, the values ​​of resistors 220 and 222 are equal). The CM dimmer circuit 104a, 108a increases or decreases the gate voltages and thus the currents of transistors 240 and 242 (similar to transistors 244 and 246) through comparators 224 and 226 and mirror transistors 228 and 234. When Vcm is greater than Vmid, comparator 224 turns off transistor 230 and comparator 226 turns on transistor 232. When Vcm is less than Vmid, comparator 224 turns on transistor 230 and comparator 226 turns off transistor 232. For example, when Vcm is higher than Vmid, comparators 224 and 226 increase the gate voltages of transistors 228 and 234. Due to this current mirroring, transistors 240 and 244 source less current and transistors 242 and 246 sink more current, and consequently, the common-mode voltage Vcm is reduced by this feedback operation.

[0022] The amount of CM current caused by a BCI event can be very large, so transistors 240, 242, 244, and 246 are designed to source and sink a portion of the CM current caused by the BCI event, which can generate hundreds of milliamperes of CM current. To source and sink this much CM current, these transistors 240, 242, 244, and 246 must operate (be biased) with a high quiescent current. However, when no BCI event occurs during normal operation, reducing the quiescent current is desirable to minimize circuit power consumption while maintaining transistors 240, 242, 244, and 246 in their saturation region (hard ON), if necessary.

[0023] For transistors 240, 242, 244, and 246 to have 200 milliampere CM current capabilities during a BCI event, and assuming a 20x current ratio, the circuit for transistors 228 and 234 can be designed to carry a maximum of 10 milliamperes. However, during normal operation, transistors 228 and 234 consume approximately half of this maximum current, or 5 milliamperes, meaning transistors 240, 242, 244, and 246 have a quiescent current of 100 milliamperes. 100 milliamperes is a tremendous current draw for just one CM dimmer circuit, and considering multiple CM dimmers are used in a data transmission system, a significant power penalty arises.

[0024] Referring to Fig. 3 is a schematic diagram of an adaptive common-mode dimmer according to a specific exemplary embodiment of this disclosure. The CM dimmers 104aa, 108aa have a similar circuit to the CM dimmers 104a, 108a shown in Fig. 2, with the addition of resistors 320, 348, 350, and 322; voltage comparators 352 and 354; and transistors 356 and 358. Resistors 320, 348, 350, and 322 are configured as a resistor ladder network to provide reference voltages Vhi, Vmid, and Vlo, where Vhi > Vmid > Vlo. The CM dimmers 104aa, 108aa shown in Fig. 3 provide both lower power consumption under normal operating conditions and high current capacity during a BCI event.

[0025] Comparators 352, 354 and transistors 356, 358 only supply additional current to transistors 228, 234 when the common-mode voltage Vcm is higher or lower than Vhi or Vlo, respectively. During normal operation, without a BCI event occurring, transistors 228 and 234 consume very little current, which is then replicated by transistors 240, 244, 242, and 246. However, when a BCI event occurs, the common-mode voltage Vcm could be higher than Vhi or lower than Vlo, depending on the amount of current injected into the SIGP and SIGN signal lines. When this occurs, transistors 228 and 234, and therefore transistors 240, 244, 242, and 246, will source and sink more current due to the additional voltage comparators 352 and 354 and transistors 356 and 358.

[0026] With reference to the previous examples, transistors 228 and 234 preferably have a maximum current of 10 milliamperes, with transistors 240, 244, 242, and 246, at a 20x current ratio, capable of handling a 200 milliampere BCI event. For illustrative purposes, but not limitation, the maximum current flowing through transistors 230 and 236 can be divided into one (1) milliampere and nine (9) milliamperes. During normal operation, the voltage Vcm is close to Vmid, so comparators 352 and 354 are turned off. Thus, no current flows through transistors 356 and 358. The current flowing through transistors 230 and 232 is approximately 0.5 milliamperes, which is the same amount of current flowing through transistors 228 and 234.There, the quiescent current flowing through transistors 240 and 242 is approximately 10 milliamperes, which represents a significant energy saving during normal operation.

[0027] The adaptive mode, implemented by voltage comparators 352 and 354 in combination with transistors 356 and 358, can be used to increase the output current capability only when needed, for example, during a BCI event. Without voltage comparators 352 and 354 and transistors 356 and 358, the output current drivers implemented by transistors 240, 244, 242, and 246 would have to operate at a large quiescent current all the time to process a BCI event.

Claims

An adaptive common-mode dimmer (104a; 108a) having a first low quiescent current operating mode and a second high quiescent current operating mode; wherein: the common-mode dimmer (104a; 108a) is configured to: couple to a two-wire transmission line (110); and maintain a common-mode voltage (Vcm) thereon at a desired common-mode reference voltage (Vmid); the two-wire transmission line (110) is configured to transmit differential signals; the common-mode dimmer (104a; 108a) is configured to operate in the first mode when the common-mode voltage (Vcm) on the two-wire transmission line (110) is between a high common-mode reference voltage (Vhi) and a low common-mode reference voltage (Vlo); and the common-mode dimmer (104a; 108a) is configured to otherwise operate in the second mode. The adaptive common mode dimmer of claim 1, wherein:the high common mode reference voltage (Vhi) is less than a power supply voltage (VDD);the desired common mode reference voltage (Vmid) is less than the high common mode reference voltage (Vhi); andthe low common mode reference voltage (Vlo) is less than the desired common mode reference voltage (Vmid) and greater than a ground or power supply common mode voltage. Adaptive common mode dimmer according to claim 2, wherein the desired common mode reference voltage (Vmid) is approximately half of the supply voltage (VDD). The adaptive common mode dimmer of any one of claims 1 to 3, wherein: a current injection (BCI) event is configured to cause the common mode voltage (Vcm) to be above the high common mode reference voltage (Vhi) or below the low common mode reference voltage (Vlo); and the common mode dimmer (104a, 108a) is in the second mode. The adaptive common-mode dimmer of claim 4, wherein: the BCI event is configured to cause at least 200 milliamperes of common-mode current on the two-wire transmission line (110); and the common-mode dimmer (104a; 108a) is configured to be in the second mode when the common-mode voltage (Vcm) is greater than the high common-mode reference voltage (Vhi) or less than the low common-mode reference voltage (Vlo). Adaptive common mode dimmer according to one of claims 1 to 5, wherein the common mode dimmer (104a; 108a) is configured to cause the common mode voltage (Vcm) to return between the high and low common mode reference voltages (Vhi, Vlo) before changing from the second mode to the first mode. Adaptive common mode dimmer according to one of claims 1 to 6, wherein, when the common mode voltage (Vcm) is above the desired common mode reference voltage (Vmid), the common mode dimmer (104a; 108a) is configured to shunt current from the two-wire transmission line (110) to a ground or common power supply reference line. Adaptive common mode dimmer according to one of claims 1 to 7, wherein, when the common mode voltage (Vcm) is below the desired common mode reference voltage (Vmid), the common mode dimmer (104a; 108a) is configured to supply current from the power supply voltage (VDD) to the two-wire transmission line (110). An adaptive common-mode dimmer comprising: a first set of current drivers (240, 244) coupled between a power supply voltage (VDD) and a two-wire transmission line (110); a second set of current drivers (242, 266) coupled between a ground or common power supply reference line and the two-wire transmission line (110); first and second voltage comparators (224, 226) comprising: outputs coupled to and controlling the first and second sets of current drivers (240, 244; 242, 266); first inputs coupled to the two-wire transmission line (110); andsecond inputs coupled to a first reference voltage (Vmid), the first reference voltage (Vmid) being less than the supply voltage (VDD) and greater than ground or the common supply voltage reference line;wherein: when a common-mode voltage (Vcm) on the two-wire transmission line (110) is greater than the first reference voltage (Vmid), the second set of current drivers (242, 246) is configured to sink more current than the first set of current drivers (240, 244) provides; when the common-mode voltage (Vcm) on the two-wire transmission line is less than the first reference voltage (Vmid), the first set of current drivers (240, 244) is configured to provide more current than the second set of current drivers (242, 246) sinks; the adaptive common-mode dimmer further comprises: a third voltage comparator (352) having: a first input coupled to a second reference voltage (Vhi); a second input configured to be coupled to the two-wire transmission line (110);andan output coupled to the second set of current drivers (242, 246) configured to increase their operating quiescent current when the common-mode voltage (Vcm) is greater than the second reference voltage (Vhi), wherein the second reference voltage (Vhi) is greater than the first reference voltage (Vmid); anda fourth voltage comparator (354) comprising:a first input coupled to a third reference voltage (Vlo);a second input coupled to the two-wire transmission line (110); andan output coupled to the first set of current drivers (240, 244) configured to increase their operating quiescent current when the common-mode voltage (Vcm) is less than the third reference voltage (Vlo), wherein the third reference voltage (Vlo) is less than the first reference voltage (Vmid); Adaptive common mode dimmer according to claim 9, wherein the first reference voltage (Vmid) is approximately half of the supply voltage (VDD). Adaptive common mode dimmer according to one of claims 9 to 10, further comprising a first buffer transistor (356) between the output of the fourth voltage comparator (354) and the first set of current drivers (240, 244). Adaptive common mode dimmer according to one of claims 9 to 11, further comprising a second buffer transistor (358) between the output of the third voltage comparator (352) and the second set of current drivers (242, 246). A system for transmitting signals over a differential transmission line (110) and having adaptive common-mode dimmers (104a, 108a) with low and high operating current quiescent modes, the system comprising: a differential signal transmitter (102) having a first adaptive common-mode dimmer (104a) coupled thereto; a differential signal receiver (106) having a second adaptive common-mode dimmer (108a) coupled thereto; and a differential signal transmission line (110) coupling the differential signal transmitter (102) and the differential signal receiver (106); wherein the first and second adaptive common-mode dimmers (104a, 108a) are implemented according to one of the adaptive common-mode dimmers of claims 1 to 12. A method of reducing the common mode voltage on a differential signal transmission line (110) using an adaptive common mode dimmer (104a, 108a) having low and high operating current quiescent modes, the method comprising the steps of operating any one of the adaptive common mode dimmers (104a, 108a) according to claims 1 to 12.

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