Signal receiving apparatus and two-stage adaptive equalization method thereof

A signal receiving apparatus includes an equalization module, a coarse tuning module and a fine tuning module. The equalization module receives an input signal, and performs an equalization process on the input signal according to an equalization strength to generate an equalized signal. The coarse tuning module adjusts the equalization strength according to the equalized signal until the equalized signal satisfies a preliminary convergence condition. When the preliminary convergence condition is satisfied, the fine tuning module adjusts the equalization strength according to the equalized signal until the equalization strength satisfies a final convergence condition.

This application claims the benefit of Taiwan application Serial No. 103102449, filed Jan. 23, 2014, the subject matter of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to a signal equalization technology.

2. Description of the Related Art

An equalizer is an essential component at receiver end of many communication systems, and is utilized for compensating or eliminating deformation/attenuation resulted from non-ideal channel factors during a transmission process. Only by applying an appropriate equalization process (e.g., selecting an appropriate equalization strength) on an input signal, a receiver end may correctly parse and use received data. Taking a DisplayPort (DP) video interface of Video Electronics Standards Association (VESA) for example, the specification states that a receiver end needs to perform an equalization process following a clock recovery process.

In earlier versions of the DP video interface, a lower operating frequency (1.62 GHz or 2.7 GHz) is used, and a receiver end is usually required to only adopt a fixed equalization strength for receiver circuits to be functional. However, in newer versions of the DP video interface, not only an operating frequency is higher (5.4 GHz) but also a fault tolerance is lower, such that the design of adopting one fixed equalization strength may result in performance degradation of a receiving apparatus.

SUMMARY OF THE INVENTION

The invention is directed to a signal receiving apparatus and a two-stage adaptive equalization method applied to the signal receiving apparatus. In embodiments of the present invention, a process of selecting equalization strength is divided into two stages of coarse tuning and fine tuning that have different convergence conditions. In addition to adaptively adjusting the equalization strength according to an input signal, the signal receiving apparatus and the equalization method of the present invention are further capable of ensuring that the final selected equalization strength is within a correct range through the inspection of the two adjustment phases.

The concept of the present invention is not limited to applications of a certain signal receiving apparatus, and may be extensively implemented to situations where adaptive equalization processing is required, e.g., an electronic device adopting a DP interface, a High-Definition Multimedia Interface (HDMI), a Mobile High-definition Link (MHL) interface, a Serial Advanced Technology Attachment (SATA) interface, and a Universal Serial Bus 3.0 (USB 3.0) interface.

A signal receiving apparatus is provided according to an embodiment of the present invention. The signal receiving apparatus includes an equalization module, a coarse tuning module and a fine tuning module. The equalization module receives an input signal, and performs an equalization process on the input signal according to an equalization strength to generate an equalized signal. The coarse tuning module adjusts the equalization strength according to the equalized signal until the equalized signal satisfies a preliminary convergence condition. When the processed signal satisfies the preliminary convergence condition, the fine tuning module adjusts the equalization strength according to the equalized signal until the equalized strength satisfies a final convergence condition.

A two-stage adaptive equalization method applied to a signal receiving apparatus is provided according to another embodiment of the present invention. An equalization process is performed on an input signal according to an equalization strength to generate an equalized signal. The equalization strength is adjusted according to the equalized signal until the processed signal satisfies a preliminary convergence condition. When the equalized signal satisfies the preliminary convergence condition, the equalization strength is adjusted again according to the equalized signal until the equalization strength satisfies a final convergence condition.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a function block diagram of a signal receiving apparatus100according to an embodiment of the present invention. In the embodiment, the signal receiving apparatus100includes an equalization module12, a coarse tuning module14, a fine tuning module16, a multiplexer18and a clock data recovery module19. The equalization module12receives an input signal, and performs an equalization process on the input signal to generate an equalized signal. The equalization strength of the equalization process may first be set to an initial value. For example, the equalization strength of the equalization process has 32 levels respectively represented as level 0 to level 31, and the initial value may be level 0, for example. In other words, the equalization module12is set to initially perform the equalization process according to the initial equalization strength.

As shown inFIG. 1, the equalized signal outputted from the equalization module12is transmitted to the clock data recovery module19to generate a recovered data signal. The multiplexer18is defaulted to select and connect the coarse tuning module14to an input end of the equalization module12. This input end receives a control signal of the equalization strength of the equalization module12. The coarse tuning module14receives the recovered data signal, and accordingly generates a coarse tuning control signal. More specifically, the coarse tuning module14adjusts the equalization strength that the equalization module12uses according to the recovered data signal, until the recovered data signal satisfies a preliminary convergence condition. For example, the coarse tuning module14first determines whether the recovered data signal corresponding to the initial equalization strength satisfies the preliminary convergence condition. If not, the coarse tuning module14changes the equalization strength (e.g., increasing the equalization strength from level 0 to level 3) through the coarse tuning control signal, and again determines whether the recovered data signal corresponding to level 3 satisfies the preliminary convergence condition. When the coarse tuning module14determines that the recovered data signal corresponding to a predetermined equalization strength satisfies the preliminary convergence condition, the coarse tuning module14stops adjusting the equalization strength, and sends a preliminary convergence notification to the multiplexer18, so as to change the multiplexer18to the fine tuning module16and the equalization module12.

In practice, the amount of the equalization strength that the coarse tuning module14updates each time is not limited to a specific value, and may be determined by a circuit designer or a user. For example, the equalization strength may change at a time according to a sequence of: level 0, level 3, level 6 . . . level 30, level 0, level 3 . . . , and so forth. Further, the circuit designer may also set upper and lower limits of the equalization strength. For example, the equalization strength may change at a time according to a sequence of: level 10, level 13, level 16, level 19, level 22, level 25, level 22, level 19, level 16, level 13, level 10 . . . , and so forth.

In actual applications, the preliminary convergence condition may be in a quantity greater than 1, and the coarse tuning module may only send the preliminary convergence notification when several preliminary convergence conditions are satisfied. In one embodiment, the coarse tuning module14generates and analyzes an eye diagram of the recovered data signal, and determines whether an expansion level of the eye diagram of the preliminary convergence condition is greater than a threshold. It should be noted that, details for generating and analyzing the eye diagram are generally known to one person skilled in the art, and shall be omitted herein.

In another embodiment, the preliminary convergence condition is whether the quantity of known symbols included in the recovered data signal is greater than a quantity threshold. As shown inFIG. 2, the coarse tuning module14may include a symbol counting unit14A, which identifies a plurality of target symbols in the recovered data signal, and counts the total quantity of the target symbols occurring within a predetermined period of time. Taking a DP interface for example, before officially transmitting video data, a transmitter end first provides a receiver end with a training sequence that includes multiple K28.5 bit strings. For a predetermined equalization strength, the symbol counting unit14A may identify and count the total quantity of the K28.5 bit strings in the corresponding recovered data signal. When the count result of the symbol counting unit14A is greater than the above quantity threshold (e.g., 500), the coarse tuning module14determines that the recovered data signal satisfies the preliminary convergence condition. Conversely, when the count result corresponding to a predetermined equalization strength does not reach the quantity threshold, the coarse tuning module14may change the equalization strength, and iterates the step of identifying and counting the target symbols. The significance of satisfying the preliminary convergence condition indicates that the current equalization strength is sufficient for subsequent circuits to substantially parse signal contents correctly.

It should be noted that, the above target symbols are not limited to K28.5 bit strings, and may be selected by a circuit designer according to specifications of actual applications. For example, an HDMI-compliant or MHL-compliant input provided to the equalization module12does not include a training sequence, and therefore the target symbols to be identified by the symbol counting unit14A may be a plurality of known control words in a blanking interval.

As shown inFIG. 1, the fine tuning module16also receives the recovered data signal and accordingly generates a fine tuning control signal. When the multiplexer18is changed to the fine tuning module16and the equalization module12by the preliminary convergence notification from the coarse tuning module14, the fine tuning module16adjusts the equalization strength that the equalization module12uses through the fine tuning control signal, until the equalization strength satisfies a final convergence condition.FIG. 3shows a detailed example of the fine tuning module16. In the embodiment, the fine tuning module16includes a search unit16A, a status determination unit16B and a strength adjustment unit16. Details of the fine tuning module16are described below.

The search unit16A identifies a plurality of data strings that match a target pattern from the recovered data signal. For example, the target pattern may be AABA, i.e., a data string having contents 1101 or 0010 in the recovered data signal.FIG. 4(A)andFIG. 4(B)show two examples of signal waveforms of data strings having contents 0010, where solid lines represent actual waveforms, and dotted lines represent ideal waveforms that are noise-free, attenuation-free and deformation-free. Sampling points I0to I3substantially correspond to respective center positions of the data bits, and sampling points Q0to Q2substantially correspond to respective intersections of every two data bits. InFIG. 4(A), sample results of the sample points I0, Q0, O1, Q1, I2, Q2and I3are sequentially 0, 0, 0, 0, 1, 0 and 0. As the sample results of the sample points I0to I3are 0, 0, 1 and 0, the search unit16A may determine that a data string that matches the target pattern is present hereabout. Similarly, inFIG. 4(B), the sample results of the sample points I0, Q0, I1, Q1, I2, Q2and I3are sequentially 0, 0, 0, 1, 1, 1 and 0. As the sample results of the sample points I0to I3are also 0, 0, 1 and 0, the search unit16A may also determine that a data string that matches the target pattern is present hereabout.

It should be noted that, instead of the above example of AABA, the target pattern adopted by the search unit16amay be programmable, and may be selectively adjusted according to specifications of actual applications.

The status determination unit16B determines whether each of the data string having the target pattern is in an over-equalization status or an under-equalization status. Referring toFIG. 4(A), the sample results of the sample points Q1and Q2at two sides of the sample point I2are both 0, and the status determination unit16B may then determine such occurrence as an under-equalization status. Because of the under-equalization status, the actual waveform is smaller than the ideal waveform, and the equalization strength needs to be increased. Referring toFIG. 4(B), the sample results of the sample points Q1and Q2at the two sides of the sample point I2are both 1, and the status determination unit16B may then determine such occurrence as an over-equalization status. Because of the over-equalization status, the actual waveform is greater than the ideal waveform, and the equalization strength needs to be decreased. Conversely, in the two situations above, if the sample results of the sample points Q1and Q2are respectively 0 and 1, or respectively 1 and 0, the equalization strength need not be adjusted.

Next, the strength adjustment unit16C selectively adjusts the equalization strength that the equalization module12uses according to the determination result of the status determination unit16B. For example, the strength adjustment unit16C may calculate the numbers of time that the over-equalization status and under-equalization status have occurred within a period of time, respectively. When a difference of subtracting the number of times of over-equalization status by the number of times of under-equalization status is greater than a difference threshold, the strength adjustment unit16C decreases (e.g., decreasing from level 16 to level 15) the equalization strength that the equalization module12uses. In contrast, when the difference of subtracting the number of times of under-equalization status by the number of times of over-equalization status is greater than the difference threshold, the strength adjustment unit16C increases (e.g., increasing from level 16 to level 17) the equalization strength that the equalization module12uses. When the difference between the number of times of over-equalization status and the number of times of under-equalization status is smaller than the difference threshold, the strength adjustment unit16C determines that the equalization strength that the equalization module12uses need not be adjusted, i.e., the current equalization strength is maintained.

In one embodiment, when the recovered data signal satisfies the preliminary convergence condition (i.e., when the multiplexer18is changed to connect to the fine tuning module16and the equalization module12), if a variance in the equalization strength used by the equalization module12is smaller than a variance threshold within a predetermined period of time, the fine tuning module16determines that the equalization strength satisfies the final convergence condition. In other words, if the fine tuning module16is not required to adjust the equalization strength used by the equalization module16for a predetermined period of time, it means that the current equalization strength has a high accuracy level. The variance threshold may be selected by a circuit designer based on actual needs, and is not limited to a specific value.FIG. 4(C)shows an exemplary corresponding relationship between the equalization strength and time. For example, after a period of time, as the variance in the equalization strength used by the equalization module12does not exceed a predetermined range REQST, the fine tuning module16may determine that the equalization strength satisfies the final convergence condition, and utilize an average of the equalization value within this period of time as the final equalization strength.

FIG. 5shows an application example of the signal receiving apparatus100. In this example, the equalized signal outputted from the equalization module12is provided to a sampling module11A. A sample result generated by the sampling module11A is transmitted to the digital clock data recovery module19. In addition to recovered data, the digital clock recovery module19further generates a recovered clock signal and a phase adjusting control code according to the sample result. A phase adjustment module11B adjusts the phase of the recovered clock signal according to the phase adjusting control code, and generates a sampling clock signal. In practice, the digital clock data recovery module19may generate the phase adjusting control code according to the quality of the recovered data, such that the sampling module11A may generate preferred sample results. It should be noted that, details of generating the phase adjusting control code according to the recovered data are generally known to one person skilled in the art, and shall be omitted herein. As shown inFIG. 5, the phase adjusting control code is also provided to the fine tuning module16. The fine tuning module16determines whether the phase adjusting control code has become almost stable and no longer fluctuates by a large range. Only when the phase adjusting control code indicates that the sampling clock signal outputted from the phase adjustment module11B satisfies a stable phase condition, the strength adjustment unit16C in the fine tuning module16starts to refer to the determination result of the status determination unit16B.

The circuit architecture inFIG. 5is applicable to a system that adopts digital clock data recovery for generating a clock signal, e.g., an HDMI interface. Compared to analog clock data recovery, digital clock data recovery needs a longer period of time for locking a clock signal to a substantially correct phase to further provide an accurate sampling clock signal. If the determination results (e.g., the sample results of the sample points I0to I3and the sample results of the sample points Q0to Q3) of the status determination unit16B are inaccurate before the sampling clock signal becomes stabilized, the strength adjustment unit16C may be caused to give misjudged results. By adding the requirement that the sampling clock signal needs to satisfy the stable phase condition, associated issues can be prevented.

FIG. 6shows another application example of the signal receiving apparatus100. As previously stated, the DP standard specifies that a receiver end needs to complete a clock recover process before performing an equalization process. In this example, the signal receiving apparatus100collaborates with a local oscillation source13A and a clock signal generation module13B. For example, the local oscillation source13A is an oscillator that provides a local oscillation signal. In normal situations, the clock signal generation module13B receives an original signal, and performs a clock recovery process on the original signal to generate a clock signal. To prevent the delay in a time point at which the clock signal generation module13B generates a locked clock signal from further delaying the subsequent signal processing, if the clock signal is still unlocked after a period of time, the clock signal generation module13B is changed to be configured to a frequency synthesizer, and to generate a substitute clock signal according to the local oscillation signal outputted from the local oscillation source13A for the use of the subsequent circuit (e.g., the signal receiving apparatus100).

FIG. 7shows another application example of the signal receiving apparatus100. In this example, the signal receiving apparatus100collaborates with a control module15, and assists in selecting a preferred transmission setting from a plurality of transmission settings. Taking the DP interface for example, the specification allows a training sequence be used as a test signal before a transmitter end officially sends video data, and determines which signal amplitude and which pre-emphasis level are more ideal for the transmitter end to transmit signals according to a test result of a receiver end. Details of collaborated operations of the signal receiving apparatus100and the control module15are given below.

After receiving a transmission system sends a first input signal according to a first transmission setting, the control module15controls the equalization module12to perform an equalization process on the first input signal, and the coarse tuning module14and the fine tuning module16sequentially select respective equalization strengths until the fine tuning module16determines that the equalization strength of the first input signal satisfies the above final convergence condition. After the fine tuning module16determines that the equalization strength of the first input signal satisfies the above final convergence condition, the control module15records a first signal quality corresponding to the first input signal. For example, the first signal quality may be the expansion level of an eye diagram of the equalized signal corresponding to the equalization strength that satisfied the final convergence condition. In practice, the first signal quality may be provided by the coarse tuning module14or the fine tuning module16to the control module15, or may be generated by the control module15according to the equalized signal outputted from the equalization module12.

After receiving a second input signal sent by the same transmission system according to a second transmission setting, the control module15controls the equalization module12to perform an equalization process on the second input signal, and the coarse tuning module14and the fine tuning module16sequentially adjust the equalization strength until the fine tuning module16determines that the equalization strength of the second input signal satisfies the final convergence condition. In practice, the first transmission setting and the second transmission setting may include different pre-emphasis levels and/or different signal amplitudes. It should be noted that the first transmission setting and the second transmission setting are not limited to including the two exemplary settings above. After the fine tuning module16determines that the equalization strength applied on the second input signal satisfies the final convergence condition, the control module15records a second signal quality corresponding to the second input signal. According to the first signal quality and the second signal quality, the control module15determines which of the first transmission setting and the second transmission setting is to the transmission system. One person skilled in the art can understand that, the number of the transmission settings that the signal receiving apparatus100and the control module15uses for testing is not limited to two; a circuit designer may determine the number of tests according to actual requirements or system specifications.

A two-stage adaptive equalization method applied to a signal receiving apparatus is provided according to another embodiment of the present invention.FIG. 8shows a flowchart of the method. In step S82, an initial value of an equalization strength is set. In step S84, an input signal is received, and an equalization process is performed on the input signal to generate an equalized signal. In step S86, the equalization strength of the equalization process is adjusted according to the equalized signal until the equalized signal generated by the equalization process satisfies a preliminary convergence condition. In step S88, when the equalization signal satisfies the preliminary convergence condition, the equalization strength of the equalization process is adjusted again according to the equalized signal until the equalization strength satisfies a final convergence condition.

FIG. 9(A)shows an exemplary partial process of an adaptive equalization method according to the present invention. In step S901, target symbols are identified from a processed signal (e.g., an equalized signal or a recovered data signal generated according to the equalized signal), and a quantity of the target symbols is calculated (e.g., the task performed by the symbol counting unit14A). In step S902, it is determined whether the total quantity of the target symbols occurring in a predetermined period is greater than a quantity threshold. The coarse tuning procedure in the adaptive equalization method ends when a determination result of step S902is affirmative. Conversely, when the determination result of step S902is negative, step S903is performed to update the equalization strength applied on the processed signal. After step S903, step S901and subsequent steps are iterated.

FIG. 9(B)shows another exemplary partial process of an adaptive equalization method according to the present invention. In step S911, it is determined whether an electronic system adopting the process is operating under a digital clock data recovery architecture (e.g., an HDMI interface). When the determination result of step S911is affirmative, step S912is performed to wait for a sampling clock signal to satisfy a stable phase condition (e.g., waiting for the phase adjusting control code inFIG. 5to become stabilized). When the determination result S911is negative, or after step S912, step S913is performed. In step S913, a data string having a predetermined pattern is identified from a processed signal (e.g., an equalized signal or a recovered data signal generated according to the equalized signal), and it is determined whether the data string having the predetermined pattern is in an over-equalization status or an under-equalization status (e.g., the tasks performed by the search unit16A and the status determination unit16B). In step S914, within a predetermined period, the number of times of over-equalization status and the number of times of under-equalization status are calculated. In step S915, it is determined whether the difference of subtracting the number of times of over-equalization status by the number of times of under-equalization status is greater than a difference threshold. When a determination result of step S915is affirmative, step S916is performed to decrease the equalization strength applied on the processed signal, followed by returning to step S913. When the determination result of step S915is negative, step S917is performed to determine whether the difference of subtracting the number of times of under-equalization status by the number of times of over-equalization status is greater than a difference threshold. When a determination result of step S915is affirmative, step S916is performed to increase the equalization strength applied on the processed signal, followed by returning to step S913. When the determination result of step S917is negative, step S919is performed to determine whether the equalization strength satisfies a final convergence condition. When a determination result of step S919is negative, the process returns to step S913. When the determination result of step S919is affirmative, step S920is performed to determine a final equalization strength (e.g., an average of the equalization strength within the period of time in which the final convergence condition is satisfied). At this point, the fine tuning procedure of the method ends.

One person skilled in the art can appreciate that, various operations and modifications in the description associated with the signal receiving apparatus100can be applied to the two-stage adaptive equalization method inFIG. 8,FIG. 9(A)andFIG. 9(B), and shall be omitted herein.

In conclusion, the present invention provides a signal receiving apparatus and a two-stage adaptive equalization method applied to the signal receiving apparatus. According to embodiments of the present invention, the procedure of selecting the equalization strength is divided into two phases having different convergence conditions. In addition to adaptively adjusting the equalization strength according to an input signal, the signal receiving apparatus and the equalization method of the present invention are further capable of ensuring that the final selected equalization strength is within a correct range through the inspection of the two adjustment phases.