# Patent

## Title
Partial response decision-feedback equalization with adaptation based on edge samples

## Abstract

A device (102) implements data reception with edge-based partial response decision feedback equalization. In an example embodiment, the device implements a tap weight adapter circuit (114) that sets the tap weights that are used for adjustment of a received data signal (104). The tap weight adapter circuit (119) sets the tap weights based on previously determined data values and input from an edge analysis of the received data signal using a set of edge samplers. The edge analysis (116) may include adjusting the sampled data signal by the tap weights determined by the tap weight adapter circuit. A clock generation circuit (220) generates an edge clock signal to control the edge sampling performed by the set of edge samplers. The edge clock signal may be generated as a function of the signals of the edge samplers and prior data values determined by the equalizer.

## Background
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the benefit of the filing date of U.S. Provisional Patent Application No. 60/859,820 filed Nov. 16, 2006, the disclosure of which is hereby incorporated herein by reference.


BACKGROUND
The performance of conventional digital systems is limited by the transmission interconnection between integrated circuits. In such systems, a transmitter sends data onto a channel by setting a signal parameter of an output signal, such as current or voltage, to one of a plurality of discrete values during each of a succession of intervals referred to herein as data intervals. The data is in turn received by a receiver on the channel. The receiving IC device needs to be able to recognize the discrete values set by the transmitter in the data so it may be used in the receiving IC device.
The transmitted data typically experiences corruption as it propagates through the channel from the transmitter to the receiver. Such corruption can cause pre and post inter-symbol interference (ISI) and make it more difficult, or impossible, for some receivers to determine the value of the signal parameter during each individual data interval. The corruption which causes ISI may arise from frequency dependent attenuation in the signal path, reflections from impedance discontinuities in the signal path, or other factors. Typically, signal components at higher frequencies are attenuated to a greater degree than signal components at lower frequencies. These problems typically become more significant in high-performance systems where data is transmitted at a high data rate.
Equalization schemes may be used in high-performance communication links to compensate for all or part of the corruption imposed by the channel and thus maintain an acceptable error rate. For example, equalization may include processes for emphasizing or attenuating a selected frequency or frequencies of a signal, often to compensate for frequency-specific attenuation of the signal.
It would be desirable to implement receivers with equalization components in such systems in a manner that improves circuit design while effectively maintaining or improving data throughput.



BRIEF DESCRIPTION OF DRAWINGS
The present technology is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements including:
FIG. 1 is a block diagram of components of an edge-based partial response decision feedback equalizer of the present receiver technology;
FIG. 2 is a further embodiment of an edge-based partial response decision feedback equalizer of the present receiver technology;
FIG. 3 is a logic diagram illustrating suitable logic that may be implemented by an edge-based tap weight adaptor circuit for one embodiment of the present technology;
FIG. 4 is an embodiment of an edge analysis circuit suitable for implementation in the edge-based partial response decision feedback equalizer of the present receiver technology;
FIG. 5 shows an example methodology that may be employed by logic circuits of a timing generator that is suitable for an equalizer of the present receiver technology;
FIG. 6A is an approximate partial response decision feedback equalizer single bit response graph with linear approximation;
FIG. 6B is an eye diagram showing data levels and transitions corresponding to the single bit response shown in FIG. 6A.



DETAILED DESCRIPTION
An equalizer circuit 102, such as the edge-based partial response decision feedback equalizer (prDFE) for receiving a data signal according to one embodiment of the present technology is illustrated in FIG. 1. The equalizer includes adjusting circuitry 106, sampling circuitry 108, selection circuitry 110, tap weight adapter circuitry 114 and edge analysis circuitry 116. As shown in FIG. 1, a transmitted data signal affected by inter-symbol interference (“ISI”) enters adjusting circuitry 106 where it is adjusted by the tap weights generated by the tap weight adapter circuitry 114. Tap weights may be derived or generated to have the same or different quantities and may also be positive and negative versions of the same tap weight or quantity (e.g., tap weight value A is equal to the absolute value of tap weight value B).
As shown in FIG. 1, the adjusting circuitry 106 produces a first adjusted signal and second adjusted signal. Typically, the first and second adjusted signals are derived based on separately combining (e.g., adding or subtracting) a tap weight to the ISI and data signal 104 to counteract, reduce or eliminate the ISI. The first and second adjusted signals are then input to the sampling circuitry 108. In the sampling circuitry 108, the respective adjusted signals are sampled to produce first and second data values.
The first and second data values are input to the selection circuitry 110. Prior received data values are also input to the selection circuitry 110. The selection circuitry 110 selects one of the first and second data values based on a prior received data value. The selected value of the selection circuitry 110 is output as the received data value 111.
As previously mentioned, the tap weight adapter circuitry 114 generates the tap weights. In this operation, the tap weights are derived with edge information input from the edge analysis circuitry 116 and received data values 111. The edge analysis circuitry 116 produces the edge information based on the received data signal 104. The edge analysis circuitry 116 may further derive the edge information using the tap weights from the tap weight adapter circuitry 114.
A further embodiment of a receiver of the present technology is illustrated in FIG. 2. As shown in FIG. 2, the received data signal 204 is input to the equalizer circuit 202. In the event that high speed data transmission is utilized, the received data signal will typically be affected by ISI as previously mentioned. The received data signal 204 is applied to adders 206A, 206B. The adders separately combine the received data signal 204 with first and second tap weight signals 207A, 207B to adjust the input data signal 204 so as to derive respective first and second adjusted signals. The tap weight signals have also been designated in FIG. 2 as the “+αedge” signal and the “−αedge” signal and may also be referred to as equalization coefficients. The purpose of this adding or adjusting operation is to cancel ISI generated by the previously received bit.
The first and second adjusted signals from adders 106A, 106B are input to data samplers 208A, 208B. Sampling operations by the data samplers are controlled by a data clock signal s-clkdata. The data clock signal s-clkdata permits sampling of the incoming signal in the data eye of the received data signal 204. The output of the data samplers 208A, 208B are then supplied to a mux 210. The mux 210 is configured for deciding or selecting between one or the other of the output signals from the data samplers 208A, 208B. A control input of the mux is connected with a prior received data value as will be discussed in more detail herein such that mux 210 can make a selection based on prior received data, which effectively decides which adjustment (e.g., either of the alpha values +αedge or −αedge) to the received data signal 204 should be utilized for the presently received data bit. The data signal output 211 from the mux 210 comprises a digital logic sequence of data values sampled from the received data signal in a manner that compensates for inter-symbol interference in the received data signal 204.
The output of the mux 210 is also fed to a data retention circuit 212. The data retention circuit 212 may be formed by a plurality of latches, flip-flops, or the like for retaining consecutive data values or bits received and produced at the output of mux 210. As illustrated in the embodiment of FIG. 2, flip-flop 212A is set in each consecutive system cycle by the output of the mux 210. The output of the flip-flop 212A sets flip-flop 212B and the output of flip-flop 212B sets flip-flop 212C. Thus, the data retention circuit 212 consecutively stores or retains data values Dk+1, Dk and Dk−1 from the mux 210 such that an immediately preceding received data value Dk+1 from the presently received data value is stored by flip-flop 212A, its immediately preceding received data value Dk is stored by flip-flop 212B and its immediately preceding received data value Dk−1 is stored by flip-flop 212C. Although three data values are stored by the data retention circuit 212 in this embodiment, fewer or more such prior data values or bits may be retained and additional latches or flip-flops provided depending on the desired control logic of additional components of the equalizer 202 as will be discussed herein.
The equalizer circuit 202 will also typically include a tap weight adapter circuit 214 for setting the tap weight signals applied to adders 207A and 207B. In this edge-based implementation, the determined tap weight signals can be a direct measure of error information attributable to ISI at the edge of the data signal eye, which in turn may be utilized to correct the data signal for making the data detection at the center of the data eye with one of the data samplers 208A, 208B. Thus, as will be explained in more detail herein, the tap weight adapter circuit 214 includes logic circuits to generate the first and second tap weight signals 207A, 207B in accordance with one or more signals from an edge analysis of the received data signal 204. Thus, one or more edge information signal 215, also designated in FIG. 2 as “Einfo”, is input to the logic circuits of the tap weight adapter circuit 214. Moreover, the tap weight adapter circuit 214 generates the first and second tap weight signals 207A, 207B in accordance with prior received data values of the data retention circuit 212. Thus, data values Dk+1, Dk and Dk−1 are input to the tap weight adapter circuit 214 for use in the logic applied by the tap weight adapter circuit 214.
Consequently, the equalizer circuit 202 of the present technology may also include an edge analysis circuit 216. The edge analysis circuit 216 is configured to conduct an edge analysis of the received data signal 204 utilizing the tap weight signals from the tap weight adapter circuit 214. The edge analysis circuit 216 will typically include edge samplers configured to sample the received data signal at an expected edge time associated with the received data signal as will be discussed in more detail herein. Thus, the edge analysis circuit 216 will operate based on input of an edge clock signal s-clkedge. In this embodiment, the output of the edge analysis circuit 216 is applied to the tap weight adapter circuit 214 as previously mentioned. The edge information signal 215 output by the tap weight adapter circuit 214 is also applied to a timing generator 220.
The equalizer circuit 202 will also typically operate in conjunction with a timing generator 220. Since components of the equalizer circuit utilize samplers for sampling the data eye of the received data signal 204 and the edges of the data eye of the received data signal 204, the timing generator 220 may generate both the data clock signal s-clkdata and the edge clock signal s-clkedge. The timing generator 220 may include components to generate the data clock signal s-clkdata by any known Clock Data Recovery (CDR) method and may include DLL and/or PLL circuit components or the like to implement the method. The timing generator 220 may then generate the edge clock signal s-clkedge by adjusting the phase of the determined s-clkdata signal to produce the edge clock signal s-clkedge.
As discussed in more detail herein, in one embodiment, logic circuits of the timing generator 220 may implement a method in generating the edge clock signal s-clkedge based on data from the received data signal 204 and edge information from the edge analysis circuit 216. Thus, data values Dk+1, Dk and Dk−1 from the data retention circuit 212 and edge information signal 215 (Einfo) from the edge analysis circuit 216 may be applied as input to the timing generator 220 so that the phase of the edge clock signal s-clkedge may be adjusted such as by controlling an increase or decrease to the phase of the signal with the logic circuits based on the data values and the edge information.
In operation, equalizer circuit 202, which can serve as an edge-based prDFE receiver, makes two speculative decisions each cycle, one assuming the previously received bit (e.g., data value Dk+1) is high and the other one assuming the previously received bit is low. This corresponds to the two adjustments made to the received data signal 204 at adders 206A, 206B based on the determined tap weight signals 207A, 207B and the two subsequent sampling operations of the resultant signals with the data samplers 208A, 208B. Once the previous bit is resolved (i.e., data value Dk+1), it is used to select the correct speculative decision. This corresponds with the control of the mux 210 by data value Dk+1 from the data retention circuit 212. In this embodiment, the top input of the MUX is selected when Dk+1 is a high value. Despite the fact that the tap weight signals 207A, 207B have been determined based on a measure of ISI at the edge of the data eye of the received data signal 204, they are nevertheless used as a measure to adjust the received data signal 204 to cancel ISI in the data eye and thereby permit more accurate sampling of data values from the data eye of the received data signal 204. This may be accomplished without the need for an extra adaptive sampler as may be utilized by other equalizer implementations.
In one embodiment of the technology, the tap weight adapter circuit 214 may be implemented with logic circuits so as to set at least one of the tap weight signals (e.g., +αedge) according to the method illustrated in FIG. 3. In the method, the αedge is initially set to zero representing no ISI at step 302. Based on the input data values Dk+1, Dk and Dk−1 from the data retention circuit 212, the method continuously checks for the condition of consecutively received data bits, such as received data bits of “110” as shown in step 304. As will be discussed in more detail herein, an implementation with this particular sequence of “110” of the received data bits will depend on which particular edge sampler of the edge analysis circuit 216 is being considered for purposes of obtaining edge information. Thus, other patterns may be implemented if based on other edge samplers. In step 304, if the “110” condition is found, process flows to step 306. In step 306, the edge information signal 215 (Einfo) from an edge sampler of the edge analysis circuit 216 is checked. If the signal is low, process flows to step 308. If the signal is high, process flows to step 310.
In step 308, the αedge tap weight signal is decreased by some nominal amount (i.e., “μ”). In step 310, the αedge tap weight signal is increased by some nominal amount (i.e., “μ”). Operational flow then returns to step 304 from both step 308 and step 310. Given the continuous operation of the equalizer circuit 214 and the tap weight adapter circuit 214, this process yields a αedge tap weight signal with a derived value that produces 50% high and 50% low signals from the utilized edge sampler of the edge analysis circuit 216. Thus, the equalizer coefficients can be continuously refined based on edge information from the received data signal. The −αedge tap weight signal 207B may be derived in parallel with the positive signal by using a negative nominal amount (i.e., “−μ”) in a comparable method to the one illustrated in FIG. 3. Alternatively, it may be determined from the αedge tap weight signal 207A by negating its value with appropriate circuit components.
In one embodiment, the edge analysis circuit 416 may be implemented as illustrated in FIG. 4. In the embodiment, the received data signal 404 is supplied to adders 406A, 406B, 406C. In adder 406A, the received data signal 404 is combined with tap weight signal 407A (i.e., +αedge). The output of adder 406A is input to an edge sampler 408A, also labeled as the “PE” or positive edge sampler. The received data signal 404 is also input to adder 406B. In the adder 406B, a null signal is added so as not to modify the received data signal 404. The adder 406B is implemented so as to maintain the respective signal synchronism between the outputs of the adders 406A, 406B, 406C. The output of adder 406B is input to an edge sampler 408B, also labeled as the “ZE” or zero edge sampler. In adder 406C, the received data signal 404 is combined with tap weight signal 407B (i.e., −αedge). The output of adder 406C is then input to an edge sampler 408C, also labeled as the “NE” or negative edge sampler. By adjusting the received data signal 404 by the tap weight signals 407A, 407B it effectively modifies the detection of input signal levels made by the edge samplers without actually modifying the thresholds of the edge samplers.
For this embodiment, the P-edge output, Z-edge output and the N-edge output shown on FIG. 4 are each applied to the timing generator 120 as three edge information signals for use by the timing generator. However, at least only one edge information signal from the edge analysis circuit may be provided to the tap weight adaptor circuit 214 as discussed with respect to the method as illustrated in FIG. 3. For example, in such an embodiment, the P-edge output signal may be applied to the tap weight adaptor circuit 214 such that its determination may be a function of or based on information of the edge of the data eye(s) of the received data signal. Nevertheless, more edge information signals may be provided to the tap weight adaptor circuit 214, such as also from the negative edge sampler, to check more than a single sampler of the edge analysis circuit 216, if desired, by modifying the steps of the method of FIG. 3 accordingly.
In one embodiment of the technology, the timing generator 220 may be implemented with logic gates so as to generate the edge clock signal s-clkedge in accordance with a method illustrated by the flow chart of FIG. 5. With each changing data value in the data retention circuit 212, logic circuits associated with the timing generator 220 will check the data values Dk−1, Dk and Dk+1 for patterns of either “110”, “010” or “101” respectively. The process uses the comparison results to decide which particular edge sampler of the edge analysis circuit 216 should be considered at sample time k+0.5 for adjusting the phase of the edge clock signal s-clkedge. Thus, at step 502, if data values Dk−1, Dk and Dk+1 are “110” respectively then output of the PE edge sampler 408A is considered at step 504. In step 504, if the PE edge sampler 408A is high, then a delay of a phase of the edge sampling signal s-clkedge will be increased by some nominal delta Δ at step 506. In step 504, if the PE edge sampler 408A is low, then the delay of a phase of the edge sampling signal s-clkedge will be decreased by some nominal delta Δ at step 508.
Moreover, at step 510, if data values Dk−1, Dk and Dk+1 are “010” respectively then output of the ZE edge sampler 408B at sample time k+0.5 is considered at step 512. In step 512, if the ZE edge sampler 408B is high, then a delay of a phase of the edge clock signal s-clkedge will be increased by some nominal Δ at step 506. In step 512, if the ZE edge sampler 408B is low, then the delay of a phase of the edge sampling signal s-clkedge will be decreased by some nominal delta Δ at step 508.
Additionally, at step 514, if data values Dk−1, Dk and Dk+1 are “101” respectively then the ZE edge sampler 408B at sample time k+0.5 is considered at step 516. In step 516, if the ZE edge sampler 408B is low, then a delay of a phase of the edge sampling signal s-clkedge will be increased by some nominal Δ at step 506. In step 516, if the ZE edge sampler 408B is high, then the delay of a phase of the edge sampling signal s-clkedge will be decreased by some nominal delta Δ at step 508.
Finally, at step 518, if data values Dk−1, Dk and Dk+1 are “001” respectively then the NE edge sampler 408C at sample time k+0.5 is considered at step 520. In step 520, if the NE edge sampler 408C is low, then a delay of a phase of the edge sampling signal s-clkedge will be increased by some nominal Δ at step 506. In step 516, if the ZE edge sampler 408A is high, then the delay of a phase of the edge sampling signal s-clkedge will be decreased by some nominal delta Δ at step 508.
Although the edge analysis circuit 216 may be constructed for operation with at least three edge samplers as previously described and shown in FIG. 4, an alternative embodiment may utilize two edge samplers, such as, the ZE edge sampler and either one of the PE and NE edge samplers. In such an embodiment, the logic circuits implemented by the timing generator 220 would then be based on two edge information signals from the edge analysis circuit 216. For example, the “Z-edge” information signal and either one of the “P-edge” information signal or the “N-edge” information signal shown in FIG. 4 may be input to the timing generator 220. In this embodiment, a method as illustrated in FIG. 5 would be implemented in the timing generator 220 to only consider “110”, “010” and “101” data value conditions (e.g., steps 502, 510 and 514 of FIG. 5) if the PE edge sampler is used with the ZE edge sampler for increasing or decreasing the clock phase delay for the edge clock signal s-clkedge. Alternatively, a method as illustrated in FIG. 5 would be implemented in the timing generator 220 to only consider “101”, “010” and “001” data value conditions (e.g., steps 510, 514 and 518 of FIG. 5) if the NE edge sampler is used with the ZE edge sampler for increasing or decreasing the clock phase delay for the edge clock signal s-clkedge.
Consequently, in this two edge sampler embodiment or the three edge sampler embodiment, the method of the logic circuits of the tap weight adapter circuit 214 as illustrated in FIG. 3 would be based on input from either the PE edge sampler or the NE edge sampler when present. Thus, at step 306 of the method illustrated in FIG. 3, if the edge analysis circuit 216 implements the PE edge sampler and the ZE edge sampler, then the sample from the PE edge sampler could be checked (as Ek+0.5) and the remaining aspects of the process of FIG. 3 would remain the same.
Alternatively, if the edge analysis circuit 216 implements the NE edge sampler and the ZE edge sampler at 306 and not the PE edge sampler in the method illustrated in FIG. 3 with respect to a two edge sampler embodiment, then the sample from the NE edge sampler would be checked at 306. Moreover, in view of the use of the NE edge sampler, in step 304 the condition that would be checked with respect to the data values would be “001” rather than “110”. Furthermore, rather than using μ at step 308 and step 310, the nominal value μ would be negated so that (−μ) was used in the process instead.
The application of edge-based sampling information to the operational adjustment of the data signal for ISI removal and the operation of the present equalizer/receiver technology may be further illustrated with respect to the graphs of FIGS. 6A and 6B. The graph of FIG. 6A represents an approximated single bit response of a channel associated with the equalizer 102 or 202 of the present technology. In the graph, time intervals associated with integers −1, 0, 1 and 2 (i.e., t−1, t0, t1, t2) represent times associated with sampling in consecutive data eyes. The time intervals associated with real numbers −0.5, 0.5, 1.5 (i.e., t−0.5, t0.5, t1.5) represent times associated with sampling at the edges of consecutive data eyes. Transmission of the single d0 data bit at the t0 time results in a d1 post-cursor ISI quantity at the t1 time and zero ISI quantity at the t2 time. The post-cursor ISI quantity d1 is also labeled “αdata” and thus represents a quantity that optimally would be removed at time t1 so that sampling of a data signal at the t1 time would not be affected by that post-cursor ISI value (αdata).
The graph of FIG. 6B shows data levels and transitions corresponding to a single bit response of the prDFE receiver of the present technology. The four points on the Tk line (e.g., 602A, 602B, 602C and 602D) along the left of the graph represent signal levels including ISI with respect to previously transmitted bits. Thus, the 602A point represents a received data signal including ISI as a result of a transmitted “11” data signal (i.e., [D−1, Dk]=[1,1]). Similarly, the 602B, 602C and 602D points represent received data signals including ISI as a result of a respectively transmitted “01”, “10” and “00” data signals.
The four points on the Tk+1 line (e.g., 604A, 604B, 604C and 604D) along the right of the graph represent signal levels including ISI as a result of a subsequent bit (e.g., Dk+1) that follows signal levels associated with the previously transmitted bits at points 602A, 602B, 602C and 602D. Thus, the 604A point represents the resultant signal with ISI for a subsequent Dk+1 bit of “1” in the received data signal following either the “11” or “01” received data signal respectively at points 602A and 602B. The 604B point represents the resultant signal with ISI for a subsequent Dk+1 bit of “1” in the received data signal following either the “10” or “00” received data signal respectively at points 602C and 602D. Similarly, the 604C and 604D points represent the resultant signal with ISI for a subsequent Dk+1 bit of “0” in the received data signal respectively following either (a) the “11” and “01” received data signal from points 602A and 602B respectively or (b) the “10” and “00” received data signal from points 602C and 602D respectively. The lines from time Tk to time Tk+1 indicate the various possible transitions that the signal may make between these times, depending on the received data bits, according to the single bit response of FIG. 6A.
Significantly, points 608A, 608B, 608C indicate three signal levels that may be detected at the edge time in conjunction with the PE, ZE and NE edge samplers respectively as previously described herein. To this end, based on the continuous operation of the methods shown in FIGS. 3 and 5 utilizing PE, ZE and NE edge samplers in the edge analysis circuit 416 shown in FIG. 4, the sampling time of the edge clock signal s-clkedge generated by the timing generator 210 will be adjusted to lock to the Φ1 time shown in FIG. 6B. This will further result in the setting of the tap weight signals 207A, 207B to a signal level associated with the quantities shown on FIG. 6B as +αedge and −αedge, which in view of the adjustment of the received data signal by these amounts, permits detection of the levels indicated by points 608A and 608C. Thus, given these tap weights use with the data samplers 208A, 208B, it thereby permits data sampling with effective sample timing and thresholds associated with points 608G and 608H, effectively compensating for the ISI amount αdata of FIG. 6A by using the αedge of FIG. 6B. That is, the level measured for point 608A is used to approximate the ideal sampling threshold of 608G for distinguishing signals at levels 604A and 604C.
In a still further alternative embodiment, the timing generator 220, edge analysis circuit 216 and tap weight adapter circuit 214 may be implemented to lock the system to an edge time other than the one associated with Φ1 shown in FIG. 6B. For example, the system may be configured to lock to an edge time associated with Φ2 shown in FIG. 6B. In this embodiment, two edge samplers of the edge analysis circuit 216 may be configured to detect the signal levels shown at points 608E and 608F. To this end, the timing generator 220 may adjust the edge clock signal s-clkedge in response to data values of “110”, “101”, “010” and/or “001” from the data retention circuit 212. Thus, an edge sampler associated with point 608E may be checked for increasing or decreasing a delay of the edge clock signal s-clkedge in response to data values of “110” and “101”. Similarly, another edge sampler associated with point 608F could be checked for increasing or decreasing a delay of the edge clock signal s-clkedge in response to data values of “001” and “010”. Either or both of these samplers may be used in the determination of the edge clock signal s-clkedge if present. However, by utilizing both, the edge clock signal is more likely to settle or lock to the desired time faster, which is the edge time associated with Φ2 in this case.
In this embodiment, the method of FIG. 3 may be used with the edge sampler associated with point 608E by checking for data values of either “110” or “101” in step 304 or with the edge sampler associated with point 608F by checking for data values of either “010” or “001” in step 304. However, in the determination of the tap weight setting with the tap weight adapter circuit in this embodiment using the steps of the method of FIG. 3, use of either of the edge samplers associated with points 608E or 608F to generate the tap weight signals as previously described would not result in an alpha value for the tap weight signals 207A, 207B that would be comparable to αdata as shown in FIG. 6B without additional adjustments. Rather, it would result in an amount shown in FIG. 6B as e1. This e1 is comparable to the edge ISI component at the t1.5 time shown in FIG. 6A. As illustrated by the line between d1 and d2 in FIG. 5A, by linear approximation, this e1 quantity may be doubled to yield a quantity comparable to the ISI component αdata. Thus, in adjusting the tap weight signals used for data sampling, the value e1 (determined by the method of FIG. 3 using an edge time associated with Φ2) may then be doubled to approximate αdata. Thus, in this embodiment, the alpha signal generated by the tap weight adapter circuit would be doubled for adders 206A, 206B associated with the data samplers 208A, 208B but would not be doubled for use by the edge samplers of the edge analysis circuit 216. This doubling may be easily accomplished by further logic of the adapter circuit 214 that effect the 2× multiplication by a digital data shift operation, or in the analog domain by an appropriate scaling block such as a current mirror with a gain of 2. In this case, the tap weight adapter circuit 214 of FIG. 2 could output the values +e1 and −e1 as alpha values for the edge analysis circuit 216 and also output two times these values (e.g., 2*(−e1) and 2*(+e1)) as alpha values for the tap weights of adders 206A, 206B. Thus, additional signal lines between the circuit elements for these different alpha values may be added to the embodiment shown in FIG. 2 as necessary. In this way, the embodiment of the system may reduce the data eye ISI component based on an analysis of the ISI component at the edges of the data eye.
The equalizer circuits 102, 202 as discussed herein may be realized on one or more integrated chips. It may be part of the integrated circuits of digital processing devices, computers, computer peripherals, graphics processing devices, etc. By way of example, the circuits may be implemented as part of a central processing unit or CPU as commonly employed in a digital computer or may be employed as an intermediary between the CPU and other circuit chips. Thus, circuits as discussed herein can be incorporated in the communication path between a processor such as a CPU and a cache memory. Thus, received data signals may be baseband data signals that are transmitted between circuit components of a common apparatus without modulation on a carrier wave or demodulation thereof. The technology may also be implemented as elements of point-to-point connections according to protocols such as PCI Express, Serial ATA and other protocols. The technology can also be used with bus connections, i.e., arrangements in which the same signal is sent to plural devices connected to the same conductors. The receiver/equalizer can even be implemented for parallel links such as buses or any other device implementing parallel communications. In other embodiments, the circuits may be an element of data input or output device controllers or the like, such as a memory controller.
For example, in a memory controller embodiment, the memory controller generally acts as the device that sends data to the memory for a writing operation and receives data back from the memory for a reading operation. The equalizer circuit 102, 202 may be implemented to receive signals sent from either or both of the memory and memory controller and may be realized in either or both of these devices.
In general, each of the circuits implemented in the technology presented herein may be constructed with electrical elements such as traces, capacitors, resistors, transistors, etc. that are based on metal oxide semiconductor (MOS) technology, but may also be implemented using other technology such as bipolar technology or any other technology in which a signal-controlled current flow may be achieved.
Furthermore, these circuits may be constructed using automated systems that fabricate integrated circuits. For example, the components and systems described may be designed as one or more integrated circuits, or a portion(s) of an integrated circuit, based on design control instructions for doing so with circuit-forming apparatus that controls the fabrication of the blocks of the integrated circuits. The instructions may be in the form of data stored in, for example, a computer-readable medium such as a magnetic tape or an optical or magnetic disk. The design control instructions typically encode data structures or other information or methods describing the circuitry that can be physically created as the blocks of the integrated circuits. Although any appropriate format may be used for such encoding, such data structures are commonly written in Caltech Intermediate Format (CIF), Calma GDS II Stream Format (GDSII), or Electronic Design Interchange Format (EDIF). Those of skill in the art of integrated circuit design can develop such data structures from schematic diagrams of the type detailed above and the corresponding descriptions and encode the data structures on computer readable medium. Those of skill in the art of integrated circuit fabrication can then use such encoded data to fabricate integrated circuits comprising one or more of the circuits described herein.
In the foregoing description and in the accompanying drawings, specific terminology and drawing symbols are set forth to provide a thorough understanding of the present technology. In some instances, the terminology and symbols may imply specific details that are not required to practice the technology. For example, although the terms “first” and “second” have been used herein, unless otherwise specified, the language is not intended to provide any specified order but merely to assist in explaining elements of the technology.
Moreover, although the technology herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the technology. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the technology. For example, the illustrative embodiments using the circuits associated with detecting tap weights based on either Φ1 or Φ2 may be combined for generating tap weights based on both detection methods such that the resulting tap weights may be combined from both determinations. Moreover, the equalizer/receivers described herein may be combined with other transmit equalization circuitry and/or error correction circuitry for maintaining good high speed signal transfer characteristics on any given transmission channel. Additionally, although wired channels are explicitly discussed, wireless channels may also be implemented with the technology such that wireless transmissions may be made between chips using wireless transmitters and receivers that operate by, for example, infrared data signals or electromagnetic data signals sent between the circuit blocks of the technology. Similarly, the channels may be implemented with capacitive, inductive and/or optical principles and can use components for such channels, such as the transmitter and receiver technology capable of transmitting data by such channels.

## Claims

1. A method comprising:
sampling a data signal having a voltage value at an expected edge time of the data signal;
generating a first alpha value and a second alpha value in dependence upon the voltage value;
adjusting the data signal by the first alpha value to derive a first adjusted signal;
adjusting the data signal by the second alpha value to derive a second adjusted signal;
sampling the first adjusted signal to output a first data value;
sampling the second adjusted signal to output a second data value; and
selecting between the first data value and the second data value as a function of a prior received data value to determine a received data value.

2. The method of claim 1 further comprising setting at least one of the first alpha value and second alpha value as a further function of the prior received data value of the data signal.

3. The method of claim 2 further comprising setting at least one of the first alpha value and second alpha value as a further function of a plurality of prior data values of the data signal.

4. The method of claim 1 wherein the expected edge time is determined as a function of a plurality of prior received data values of the data signal and edge sampling of the data signal.

5. The method of claim 1 wherein generating a first alpha value and a second alpha value in dependence upon the voltage value includes generating a single value, and selecting the first alpha value and the second alpha value to respectively be positive and negative versions of a single tap weight based upon the single value.

6. The method of claim 1 wherein generating a first alpha value and a second alpha value includes selecting the first alpha value and the second alpha value in direct dependence upon the voltage value.

7. An apparatus for receiving a data signal comprising:
an adjusting circuit that adjusts the data signal with respect to a first threshold, to generate a first adjusted signal, and with respect to a second threshold, to generate a second adjusted signal respectively;
sampling and selection circuitry to generate sampled data based on one of the first adjusted signal or the second adjusted signal; and
a threshold generating circuit that samples a voltage level of the data signal at an expected data edge, and that generates at least one of the thresholds in dependence upon the voltage level.

8. The apparatus of claim 7 wherein the threshold generating circuit generates the first and second thresholds as positive and negative versions of a single equalizer tap weight, respectively.

9. The apparatus of claim 7 wherein the threshold generating circuit generates the first and second thresholds in dependence upon at least one prior data value of the sampled data.

10. The apparatus of claim 9 wherein the sampling and selection circuitry includes first and second samplers that receive the first adjusted signal and the second adjusted signal, respectively, and a multiplexer used to select between outputs of the first and second samplers to generate the sampled data.

11. The apparatus of claim 10 wherein a selection control input of the multiplexer is responsive to at least one prior data value of the sampled data.

12. The apparatus of claim 7 wherein at least one of the thresholds is a multiple of an edge measured inter-symbol interference value.

13. The apparatus of claim 12 wherein the threshold generating circuit includes a positive edge sampler to sample the data signal modified by at least one of first and second equalizer tap weight signals.

14. The apparatus of claim 13 wherein the threshold generating circuit includes a negative edge sampler to sample the data signal modified by the other one of the first and second equalizer tap weight signals.

15. A receiver circuit comprising:
a partial response equalizer to receive an input data signal and apply respective equalizer coefficients to the input data signal, the partial response equalizer including parallel decision paths to provide respective sampled signals for selection at a data output based on values of prior data outputs; and
where the equalizer coefficients are based on edge-error information associated with the input data signal.

16. The receiver circuit of claim 14 where each decision path comprises:
input circuitry to adjust the input data signal by the equalizer coefficients to generate an adjusted signal, and
sampling circuitry to sample the adjusted signal.

17. The receiver circuit of claim 16 where the sampling circuitry in each decision path comprises an edge sampler that forms a portion of an edge analysis circuit, the edge analysis circuit to generate the edge-error information.

18. The receiver circuit of claim 17 wherein the edge analysis circuit is responsive to a phase of an edge clock signal, the edge clock phase based on a sequence of adjusted signals.

19. The receiver circuit of claim 14 where the edge-error information comprises a sampled voltage value of the data signal at an expected edge time of the data signal.

20. The receiver circuit of claim 14 where the equalizer coefficients are of equal magnitude but opposite polarity.

21. The receiver circuit of claim 14 where the equalizer coefficients are also based on prior data output values.

22. The receiver circuit of claim 21 where the prior data output values comprise a sequence of adjusted signals.

23. A method comprising:
detecting edge-error information associated with a received data signal; and
equalizing the received data signal along parallel decision paths by applying respective equalizer coefficients to the data signal, where the equalizer coefficients are based on the edge-error information.

24. The method of claim 23 where the detecting comprises:
sampling the data signal at an expected edge time of the data signal in response to an edge clock signal.

25. The method of claim 24 further comprising adjusting a phase of the edge clock signal based on the error information and at least one prior data signal.

26. A receiver circuit comprising:
a partial response equalizer to receive an input data signal and apply respective equalizer coefficients to the input data signal; and
where the equalizer coefficients are based on edge-error information associated with the input data signal, the edge-error information including a sampled voltage value of the data signal at an expected edge time of the data signal.