Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
  • H04L25/40—Transmitting circuits; Receiving circuits
  • H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
  • H04L25/4917—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using multilevel codes
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
  • H03K5/153—Arrangements in which a pulse is delivered at the instant when a predetermined characteristic of an input signal is present or at a fixed time interval after this instant
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
  • H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
  • H04B7/0682—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission using phase diversity (e.g. phase sweeping)
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0264—Arrangements for coupling to transmission lines
  • H04L25/0272—Arrangements for coupling to multiple lines, e.g. for differential transmission
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03006—Arrangements for removing intersymbol interference
  • H04L25/03343—Arrangements at the transmitter end
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
  • H04L25/03878—Line equalisers; line build-out devices
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/14—Channel dividing arrangements, i.e. in which a single bit stream is divided between several baseband channels and reassembled at the receiver
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
  • H04L25/40—Transmitting circuits; Receiving circuits
  • H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
  • H04L25/4917—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using multilevel codes
  • H04L25/4923—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems using multilevel codes using ternary codes

Definitions

• This application relates to a three-transmitter multi-phase system, and more particularly to a three-phase transmitter multi-phase system with mid-level adaptive equalization.
• SERDES serializer/deserializer
• a SERDES transmitter serializes a multi-bit word into a series of corresponding bits for transmission to a receiver. There can then be no such skew between adjacent bits on a multi-wire bus since a single transmission line (which may be differential) is used in a SERDES system.
• the SERDES receiver deserializes the received serial bit stream into the original word.
• the SERDES transmission line and the receiver load introduce distortion as the data transmission rate exceeds, for example, 10 GHz.
• Adjacent bits in the serial bit stream then begin to interfere with each other.
• a three-phase signaling protocol has been developed in which three transmitters drive three separate transmission lines.
• one transmitter drives it output signal to a high voltage
• another transmitter drives its output signal to a mid-level voltage
• a remaining transmitter drives its output signal to a low voltage.
• the high voltage transmitter and low voltage transmitter may be deemed to form an active pair. From a set of three transmitters, there are three distinct pairs of transmitters that can be active. Within each pair, there are two possibilities depending upon which transmitter is high versus which transmitter is low. There are thus six distinct combinations of output signals in a three-transmitter multi-phase system. Each distinct combination of output signals may be denoted as a multi-phase symbol.
• each transmitted symbol represents 2.5 bits. In this fashion, data transmission speeds may be more than doubled over binary transmission at the same symbol rate using a single channel, albeit at the cost of increased power consumption.
• a frontend circuit decodes the received transmitter output signals to produce the corresponding binary symbol.
• the six different symbols may be represented by six binary words:
• a three-transmitter multi-phase system is provided with intelligent equalization that selectively emphasizes and de-emphasizes rising and falling edges for the mid-level transitions of transmitter output signals (transitions to or from the mid- level output voltage).
• a logic circuit controls the emphasis and de-emphasis depending upon the transition from a previous multi-phase symbol to a current multi-phase symbol.
• Each transmitter output signal transitions uniquely into a high voltage, mid- level voltage or a low voltage for each multi-phase symbol.
• the resulting selective emphasis and de-emphasis of just the mid-level transitions advantageously reduces power consumption compared to an application of traditional equalization while reducing data jitter.
• Figure 1 is a block diagram of an example three-transmitter multi-phase system configured for intelligent equalization in accordance with an aspect of the disclosure.
• Figure 2A illustrates a transition from one multi-phase symbol to another in which a first transmitter output signal transitions from VOH to VM and in which a second transmitter output signal transitions from VM to VOL without equalization.
• Figure 2B illustrates the multi-phase symbol transition of Figure 2A modified by the application of intelligent equalization such that a falling edge for the first transmitter output signal is emphasized and such that a falling edge for the second transmitter output signal is de-emphasized.
• Figure 3 illustrates a transition from one multi-phase symbol to another in which a first transmitter output signal transitions from VM to VOH and in which a second transmitter output signal transitions from VOL to VM with and without the application of intelligent equalization that de-emphasizes a rising edge for the first transmitter output signal and emphasized a rising edge for the second transmitter output signal.
• Figure 4 illustrates the transmitter output signals for a series of multiphase symbols with and without the application of intelligent equalization.
• Figure 5 illustrates the reduction of the unit interval variation from the application of intelligent equalization.
• Figure 6 is an example circuit diagram for a transmitter in the system of Figure 1.
• Figure 7 illustrates example voltage levels for a transmitter output signal in the system of Figure 1.
• Figure 8 is a flowchart of an example method of operation for a three- transmitter system having intelligent equalization in accordance with an aspect of the disclosure.
• a three-transmitter multi -phase system is provided with an intelligent equalization technique.
• the equalization technique is denoted as "intelligent" as it is adaptive to the various transitions that are possible for each transmitter output signal. Some transitions (rising edges or falling edges) are emphasized whereas other types of transitions are actually de-emphasized. Moreover, some transitions are neither emphasized nor de-emphasized.
• An encoder 135 encodes an input data stream into consecutive multi-phase symbols.
• Each multi-phase symbol has three components, corresponding to the states for the output signals for a first transmitter 105, a second transmitter 1 10, and a third transmitter 115.
• Each transmitter drives a corresponding transmission line.
• First transmitter 105 drivers a first transmission line 120 with a transmitter output signal A whereas second transmitter 110 drives a second transmission line 125 with a transmitter output signal B.
• third transmitter 115 drives a third transmission line 130 with a transmitter output signal C.
• each output signal A, B, and C may be deemed to include a plurality of levels such as a high level, a mid-level and a low level. In a voltage-mode embodiment, these level are all voltage levels. Conversely, in a current-mode embodiment, the signal levels are all current levels.
• the selective emphasis and de-emphasis of rising and falling edges for the transmitter output signals disclosed herein involves the use of additional signal levels.
• the falling edge transition of an output signal from the mid-level to the low level may be emphasized by transitioning the output signal to a reduced mid-level that is less than the mid-level during an initial portion of a current multi-phase symbol. This output signal may then be returned to the mid-level for a remainder of the multi-phase symbol.
• the falling edge transition of an output signal from the mid-level to the low level may be selectively de-emphasized by first transitioning the output signal to an increased low level during the initial portion of the current multi-phase symbol. The increased low level is greater than the low level but less than the reduced mid-level.
• encoder 135 commands each transmitter to drive its transmission line with either a high voltage, a low voltage, or an intermediate voltage.
• VOH the high voltage
• VOL the low voltage
• VM the intermediate (mid-level) voltage
• VOH is higher than VOL.
• VM can equal (VOH-VOL)/2 or some other intermediate voltage that is less than VOH but greater than VOL.
• each multi-phase symbol for system 100 involves the driving of one of the transmission lines with VOH, another with VM, and a remaining one with VOL.
• encoder 135 can command a particular transmitter to pull up (PU) its output voltage towards VOH or pull down (PD) its output voltage towards VOL.
• encoder 135 can command a particular to mid-range (PM) its output voltage to VM.
• encoder 135 There are thus three possible commands from encoder 135 to each transmitter.
• the PU, PD, and PM commands to first transmitter 105 are denoted as PU1, PD1, and PM1. Only one of these commands may be asserted for any given symbol transmission.
• encoder can assert one of a PU2, PD2, and PM2 command to second transmitter 110 and can assert one of a PU3, PD3, and PM3 command to third transmitter 115. It will be appreciated that in alternative
• the PM commands may be omitted in that an assertion of the PM command to a particular transmitter may be indicated by de-asserting both the corresponding PU command and the corresponding PD command.
• FIG. 2A An example transition from one symbol to another (each symbol being represented by the VOH/VM/VOL states for the three transmitters) may be as shown in Figure 2A.
• the output signals of the three transmitters are designated as A, B, and C.
• Transmitter output signal A in the first symbol is at VOH whereas transmitter output signal B is at VM and transmitter output signal C is at VOL.
• transmitter output signal A transitions to VM
• transmitter output signal B transitions to VOL
• transmitter output signal C transitions to VOH.
• the boundary between the two symbols occurs at time tl .
• the transmitter output signal C crosses (equals) the transmitter output signal B at a time 200 that equals tl - D, where D is a timing offset.
• the transmitter output signal A equals transmitter output signal C at a time 205 that equals tl + D.
• the timing offsets increase data jitter. At relatively low symbol rates, such data jitter may be tolerable but becomes increasingly intolerable at higher symbol rates.
• both emphasis and de-emphasis may be applied as shown in Figure 2B.
• the falling edge transition of transmitter output signal A that transitions from VOH to VM is emphasized such that transmitter output A is initially discharged at an enhanced rate to a reduced intermediate voltage Vem2 that is lower than mid-level voltage Vm.
• this emphasis is released so that transmitter output signal A returns to its intended value of VM.
• the falling edge transition of transmitter output signal B transitioning from VM to VOL is de-emphasized such that transmitter output signal B is initially discharged at a de- emphasized rate to an increased low voltage VOL EQl that is higher than VOL.
• transmitter output signal B can return to its intended value of VOL.
• An intersection at a time 210 of transmitter output signal C with transmitter output signal B is this delayed with respect to time 200 of Figure 2A.
• an intersection at a time 215 of transmitter output signal C with transmitter output signal A is advanced in time as compared to time 205 of Figure 2A. This is quite advantageous as the offset between times 210 and 215 from time tl is reduced as compared to the timing offsets of times 200 and 205 from time tl.
• a logic circuit 140 controls the intelligent equalization such as for transmitter output signals A and B as discussed with regard to Figure 2B.
• Logic circuit 140 compares the intended VOH, VM, or VOL state for each transmitter output signal in a current symbol to the corresponding VOH, VM, or VOL state for each transmitter output signal in the preceding symbol to determine the applicable intelligent equalization.
• a memory 145 may store the previous states for the transmitter output signals. If logic circuit 140 detects a transition from VOH to VM for one transmitter output signal in conjunction with a transition from VM to VOL for another transmitter output signal, it controls the corresponding transmitters to apply the emphasis and de-emphasis discussed with regard to Figure 2B.
• Figure 2B is thus directed to the intelligent equalization of a transition from VOH to VM for one transmitter output signal in conjunction with a transition from VM to VOL for another transmitter output signal.
• An analogous intelligent equalization may be applied in a transition from VOL to VM for one transmitter output signal in conjunction with a transition from VM to VOH for another transmitter output signal.
• An example transition between a first symbol and a second symbol is shown at a time tl in Figure 3.
• Transmitter output signal B equals VM in a first symbol and then transitions to VOH in a second symbol.
• a no-equalization rising edge 300 for transmitter output signal B is also shown in Figure 3.
• Rising edge 300 intersects with a falling edge for transmitter output signal A at a time 301.
• time 301 There is a substantial timing offset between time 301 and the ideal symbol transition time of tl.
• the rising edge for transmitter output signal B is de-emphasized such that transmitter output signal B rises at a reduced rate to a reduced high voltage VOH EQ2 that is less than VOH.
• VOH EQ2 a reduced high voltage
• This de-emphasis is released around the midpoint of the second symbol such that transmitter output signal B returns to its intended value of VOH for the latter portion of the second symbol.
• the de-emphasized rising edge for transmitter output B intersects with transmitter output signal A at a time 305 that is delayed with regard to time 301.
• the offset between time 305 and tl is thus reduced as compared to the offset between time 301 and time tl.
• Transmitter output signal C equals VOL in the first symbol and transitions to VM in the second symbol.
• a rising edge 310 without equalization for transmitter output signal C is also shown in Figure 3 to better illustrate the advantages of the intelligent equalization.
• Rising edge 310 intersects with transmitter output signal A at time 315 that is delayed by the timing offset from the ideal symbol transition time of tl .
• the rising edge for transmitter output signal C is emphasized such that it rises at a faster rate to an enhanced midrange voltage Veml that is higher than VM.
• This emphasized rising edge for transmitter output signal C intersects with transmitter output signal A at a time 320 that is advanced compared to time 315.
• the offset between time 320 and time tl is thus reduced as compared to the offset between time 315 and time tl.
• the resulting intelligent equalization for transmitter output signals B and C reduces the jitter in the transition from the first symbol to the second symbol.
• a transmitter output signal remains at VOH for two consecutive symbols.
• a transmitter output signal remains at VOL for two consecutive symbols.
• the first symbol and a second symbol form the transition discussed with regard to Figures 2 A and 2B.
• falling edges 400 and 405 for transmitter output signals A and B, respectively are produced with intelligent equalization whereas corresponding falling edges 410 and 415 are produced without any equalization.
• a fourth symbol and a fifth symbol form the transition discussed with regard to Figure 3.
• rising edges 420 and 425 for transmitter output signals C and A, respectively are produced with intelligent equalization whereas corresponding rising edges 430 and 435 are produced without any equalization.
• transmitter output signal C remains at VOH (without any equalization). Since at least two transmitter output signals must change state from one symbol to another so that a receiver may extract a clock signal, transmitter output signal B goes from VOL to VM in the transition from the second symbol to the third symbol whereas transmitter output signal A discharges from VM to VOL.
• a rising edge 440 for transmitter output signal B may thus be emphasized such that transmitter output signal B rises at an increased rate to the voltage Veml that is higher than VM for a first portion of the third symbol.
• a rising edge 445 for transmitter output signal B is also shown in Figure 4 to illustrate a no-equalization result.
• a falling edge 450 for transmitter output signal A may be emphasized such that transmitter output signal A falls at an enhanced rate to a voltage VOLJEQl that is lower than VOL.
• a falling edge 455 for transmitter output signal A illustrates a no-equalization result.
• emphasized edges 440 and 450 concern transitions between the midlevel voltage VM and VOL. As discussed previously, emphasizing such transitions does not consume as much power as emphasizing transitions between VOL and VOH yet still significantly reduces data jitter.
• transmitter output signal C is discharged to a voltage VOHJEQ2 that is lower than VOH for the duration of the third symbol. In this fashion, transmitter output signal C can be discharged more quickly in a subsequent symbol to either VM or VOL.
• transmitter output signal A In a transition from the third symbol to a fourth symbol, transmitter output signal A remains at VOL in the absence of any equalization. However, in the same transition with intelligent equalization, transmitter output signal A is charged to the voltage VOLJEQl (discussed with regard to Figure 2B) that is higher than VOL for the duration of the third symbol. In this fashion, transmitter output signal A can be charged more quickly in a subsequent symbol to either VM or VOH. Since there must be a transition for the transmitter output signals in every symbol for clock extraction at the receiver, transmitter output signal B transitions from VM to VOH at the beginning of the fourth symbol in an embodiment without equalization through rising edge 460.
• VOLJEQl discussed with regard to Figure 2B
• An emphasized rising edge 465 represents the result with intelligent equalization such that transmitter output signal B rises at an enhanced rate the voltage VOH_EQl that is higher than VOH for a first portion of the fourth symbol.
• a falling edge for 470 for transmitter output signal C is emphasized such that transmitter output signal C falls to Vem2 (discussed with regard to Figure 2B) for the first portion of the fourth symbol.
• a falling edge 475 illustrates the transition for transmitter output signal C without equalization. Note that the emphasis for edges 465 and 470 concern transitions between VM and VOH such that their emphasis does not consume significant power yet significantly reduces data jitter.
• transmitter output signal C transitions from VOH to VOL.
• transmitter output signal B transitions from VOL to VOH.
• Emphasizing such full-rail edges would consume power. Thus, it is "intelligent" for no emphasis to be applied to either of these edges. However, these edges may be emphasized in alternative embodiments.
• a duration 480 of the second symbol equals Ul + D, where D is a time offset. But after the application of intelligent equalization, a duration 485 of the second symbol becomes UI + D - X, where X is the adjustment from the intelligent equalization.
• a duration 490 of the third symbol is UI with intelligent equalization as is a duration 495 without intelligent equalization.
• a duration 486 of the fourth symbol without equalization is UI - D. But a duration 487 of the fourth symbol with intelligent equalization is increased to UI - D + X so as to more closely match the ideal symbol interval of UI.
• the resulting advantageous adjustment of the various symbol durations by intelligent equalization towards the desired value of UI is summarized in Figure 5.
• the application of intelligent equalization may also be denoted as an application of adaptive mid-level equalization since only the rising and falling edges from or to the mid-level voltage VM are either emphasized (or de-emphasized).
• the total UI variation without equalization is 2D whereas it is merely 2X after application of intelligent equalization. Since X is less than D, the resulting UI variation is thus significantly reduced, which reduces data jitter accordingly.
• logic circuit 140 and memory 145 comprise a means for means for selectively emphasizing a first falling edge for an output signal from a first one of the transmitters that is transitioning from the high voltage to the mid-level voltage and for selectively de-emphasizing a second falling edge for another output signal from a second one of the transmitters that is transitioning from the mid-level voltage to the low voltage.
• each transmitter 105, 110, and 115 discussed with regard to Figure 1 may be implemented as shown in Figure 6 for a transmitter 600.
• encoder 135 determines the VOH, VM, and VOL state for each transmitter. These states are the non-emphasized states discussed with regard to Figures 2B, 3, and 4 for the transmitter output signals. For example, if the pull-up signal PUl is asserted while corresponding pull-down signal PDl and mid-level signal PMl for transmitter 105 are de-asserted, corresponding transmitter output signal A is charged to VOH without equalization. In that case, transmitter output signals B and C must be uniquely assigned to either VM or VOL.
• encoder 135 may provide the no- equalization state for the current symbol (which transmitter output signal is to be VOH, which is to be VM, and which is to be VOL).
• control signals PUl, PDl, PMl, PU2, PD2, PM2, PU3, PD3, and PM3 to logic circuit 140.
• These same signals for the previous symbol are stored in memory 145 so that logic circuit 140 can compare the state for the previous symbol to the state for the current symbol to control the application of intelligent equalization accordingly.
• the control signals from logic circuit 140 to control the application of intelligent equalization depend upon the particular circuit implementation for each transmitter 105, 110, and 115.
• a plurality of voltage regulators may be used to provide a corresponding plurality of regulated voltage levels.
• a first linear dropout regulator LDOl, not illustrated
• a second LDO L02, not illustrated
• a second drive voltage e.g., 0.5 * Vdrv.
• Transmitter 600 is thus configured to provide these "non-emphasized" voltage levels for the duration of a symbol (the conventional VOH, VM, and VOL levels).
• transmitter 600 includes an NMOS pull-up transistor 605 in series with a pull-up resistor R_up.
• the source of pull-up transistor 605 couples to the pull-up resistor R_up whereas its drain is charged to the power supply voltage Vdrv by LDOl.
• the pull-up resistor R_up couples to an output node 610 for providing the transmitter output signal.
• a pull-up signal PU (a corresponding one of signals PUl, PU2, and PU3 discussed with regard to Figure 1) drives the gate of pull-up transistor 605.
• the resistance of the pull- up resistor R_up along with an input resistance of the receiver (not illustrated) receiving the transmitter output signal forms a voltage divider that divides the power supply voltage Vdrv from LDOl to charge output node 610 to VOH when pull-up signal PU is asserted.
• An analogous pull-down NMOS transistor 615 and pull-down resistor R_dn couple between output node 610 and ground.
• a pull-down signal PD (a corresponding one of signals PD1, PD2, and PD3 discussed with regard to Figure 1) drives the gate of pull-down transistor 615 such that output node 610 is discharged to VOL upon the assertion of pull-down signal PU.
• a serial combination of an NMOS mid-level transistor 620 and a mid-level resistor R_mid couple between a power supply node for the second LDO (LD02) and output node 610.
• a mid-level signal PM (a corresponding one of signals PM1, PM2, and PM3) drives the gate of mid-level transistor 620 such that output node 610 is charged to VM upon the assertion of mid- level signal PM (in the absence of intelligent equalization).
• transmitter 600 includes an NMOS emphasized pull-up transistor 625 in series with an emphasized pull-up resistor R_eup that couples to output node 610.
• LDOl drives a drain of emphasized pull-up transistor 625 with the power supply voltage Vdrv.
• An emphasized pull-up signal EPU1 drives the gate of transistor 625.
• the resistance of emphasized pull-up resistor R_eup is less than that of the pull-up resistor R_up such that when both PU and EPU1 are asserted, output node 6 0 is charged to VOH EQl . This emphasis may then be released midway through the symbol such that just pull-up transistor 605 remains on for the duration of the symbol to allow the transmitter output signal to drop to VOH.
• pull-down signal PD is asserted in conjunction with the assertion of an emphasized pull-down signal EPD1 that drives a gate of an NMOS emphasized pull-down transistor 640 in series with an emphasized pull-down resi stor R_edn that couples to output node 610.
• Pull-down resistor R_dn and emphasized pull-down resistor R_edn are then coupled in parallel to output node 610 to produce a resistance that is less than a resistance for pull-down resistor R_dn.
• Output node 610 is then discharged to VOL_EQ2, At some point in the current symbol (such as the midpoint), emphasized pull-down signal EPD1 is released (de-asserted) so that output node 610 recovers to VOL.
• a control signal EPMl is asserted to a voltage divider formed by a serial combination of an NMOS transistor 630, a resistor R_emid_upl, a resistor R_emid_dnl, and an NMOS transistor 635.
• Transistor 630 and resistor R_emid_upl couple between the power supply node from LDOl and output node 610.
• transistor 635 and resistor R_emid_dnl couple between the power supply node 610 and ground.
• Control signal EPMl drives the gate transistors 630 and 635 to divide the power supply node Vdrv into the increased mid-level voltage Veml.
• An analogous voltage divider including a pair of transistors 650 and 644, a resistor R_emid_up2, and a resistor R_emid_dn2 produce the reduced mid-level voltage Vem2 at output node 610 in response to the assertion of a control signal EMP2.
• VOH, VM, and VOL are the traditional (no equalization) voltage levels. Each of the voltage levels may be either emphasized or de-emphasized. VOH may thus be emphasized into VOH EQ1. Similarly, VM may be emphasized into Veml whereas VOL may be emphasized into VOL_EQ2. Similarly, VOH may be de-emphasized into VOH_EQ2, VM may be de-emphasized into Vem2, and VOL de-emphasized into VOL_EQl.
• the method includes an act 800 of encoding an input data signal into a current command corresponding to a current one of the successive multi-phase symbols.
• Encoder 135 encoding the input data stream into the commands (e.g., PU1, PD1, PM1 , etc.) corresponding to the various multi-phase symbols is an example of act 800.
• the method further includes an act 805 of comparing the current command to a previous state for an output signal from each of the three transmitters during a preceding one of the successive multi-phase symbols to detect when the current command commands a mid-level one of the transmitters to transition its output signal from a high-level to a mid-level and commands a low-level one of the transmitters to transition its output signal from the mid-level to a low-level.
• act 805 The detection by logic circuit 140 using the previous state stored in memory 145 to detect the transitions by output signals A and B as discussed with regard to Figure 2A is an example of act 805.
• the method includes an act 810 of responsive to detection of the mid-level transmitter and the low-level transmitter, forcing the mid- level transmitter to instead transition its output signal to a reduced mid-level during an initial portion of a current one of the successive multi-phase symbol whi le forcing the low-level transmitter to instead transition its output signal to an increased low-level, wherein the high-level is greater than the mid-level, the mid-level is greater than the reduced mid-level, the reduced mid-level is greater than the increased low-level, and the increased low-level is greater than the low -level.

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• Dc Digital Transmission (AREA)
• Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)

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