Passive Variable Continuous-Time Linear Equalizer with Attenuation and Frequency Control

Abstract

A continuous or step-variable passive noise filter for removing noise added by a test and measurement instrument channel from a signal received from a DUT. The noise filter can include, for example, a splitter that separates the signal into at least a first separated signal and a second separated signal. A first path receives the first separated signal and includes a variable attenuator and / or a variable delay line, which can be set based on the channel response of the connected DUT. The variable attenuator and / or the variable delay line can be continuously or step-variable, which will be discussed in more detail below. A second path is also included to receive the second separated signal, and a combiner combines the signal from the first path and the signal from the second path into a combined signal.

Description

[0001] Priority

[0002] This disclosure is a partial continuation application of U.S. Non - Provisional Application No. 15 / 721,591, entitled "VARIABLE PASSIVE NETWORK NOISE FILTER FOR NOISE REDUCTION", filed on September 29, 2017, which claims the priority of U.S. Provisional Application No. 62 / 414,455, entitled "CTLE VARIABLE PASSIVE NETWORK NOISE FILTER FOR NOISE REDUCTION", and both are incorporated herein by reference in their entirety. This disclosure also claims the benefit of U.S. Provisional Application No. 62 / 626,622, entitled "PASSIVE VARIABLE CTLE WITH ATTENUATION AND FREQUENCY CONTROL", filed on February 5, 2018, which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure relates to systems and methods associated with aspects of test and measurement systems, and more particularly, to systems and methods for controlling noise and frequency attenuation in test and measurement systems. Background Art

[0004] Test and measurement systems are designed to, for example, receive signal inputs from a device under test (DUT), sample the signals, and display the results as waveforms. The input channels of test and measurement systems can add noise to the signals from the DUT. Sometimes, customized fixed passive noise filters can be constructed to filter out the noise added to the signals by the test and measurement systems. However, the noise filters depend on the channel characteristics of the test and measurement instruments and the type of signals received from the DUT. For a customized fixed noise filter to be beneficial, a user would need to have on hand multiple various fixed noise filters to best match the losses and data rates of the channels used to test the DUT. These various different fixed noise filters are expensive, and it can be difficult to record which noise filter is needed for a given test scenario.

[0005] Some active noise filters are programmable and can be used in place of customized fixed passive noise filters. However, these programmable active noise filters often create too much noise to be useful in a wide variety of scenarios. In addition, the bandwidth of these programmable active noise filters often cannot be scaled up to higher bandwidths, such as 70 GHz. What is needed is a broadband noise filter that minimizes the use of multiple components and maximizes the achievable bandwidth.

[0006] Embodiments of the present disclosure address these and other deficiencies of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Aspects, features, and advantages of embodiments of the present disclosure will become apparent from the following description of embodiments with reference to the accompanying drawings, in which:

[0008] Figure 1 is an example block diagram of a noise filter having a variable attenuator and / or variable delay line according to some embodiments of the present disclosure.

[0009] Figure 2 is another example block diagram of a noise filter having a variable attenuator and / or variable delay line according to other embodiments of the present disclosure.

[0010] Figure 3 is another example block diagram of a noise filter having a multiplexer according to other embodiments of the present disclosure, the multiplexer separating an input signal into a high-band signal and a low-band signal, and the noise filter further including a variable attenuator and / or variable delay line.

[0011] Figure 4 is another example block diagram of a noise filter for differential signals using cross-coupling of a positive signal and a negative signal according to other embodiments of the present disclosure.

[0012] Figure 5 is another example block diagram of a noise filter for differential signals without cross-coupling according to other embodiments of the present disclosure.

[0013] Figure 6 is another exemplary block diagram of a noise filter for differential signals, which has a multiplexer that separates a positive input signal and a negative input signal into a high-band signal and a low-band signal. DETAILED DESCRIPTION

[0014] Disclosed herein is a continuously or step-variable passive noise filter for removing noise added by a test and measurement instrument channel from a signal received from a DUT. The noise filter may include, for example, a splitter configured to separate the signal into at least a first separated signal and a second separated signal, each of the first and second separated signals. A first path receives the first separated signal and includes a variable attenuator and / or variable delay line, which may be set based on the test and measurement instrument channel to which the DUT is connected. The variable attenuator and / or variable delay line may be continuous or stepped, which will be discussed in more detail below. A second path is also included to receive the second separated signal, and a combiner combines the signal from the first path and the signal from the second path into a combined signal.

[0015] The second path may include a fixed delay line and, in some instances, may be a reference signal. The signal in the first path is delayed and attenuated to adjust for noise added by the test and measurement instrument, and then the signal in the first path is subtracted from the reference signal on the second path to determine the input signal without the noise added by the test and measurement instrument channel. The various embodiments of such a noise filter are discussed below with respect to Figure 1-6 to discuss various embodiments of such a noise filter.

[0016] Embodiments of the present disclosure provide improvements by reducing noise in a test and measurement instrument and allowing the test and measurement instrument channel to have a frequency response with a continuous-time linear equalizer (CTLE) shaped response. The reduction in noise can be achieved without having to maintain multiple different CTLE filters on hand and without having to replace filters based on a particular test scenario - rather, the variable attenuator and / or variable delay line can be programmed or set based on the needs of the test. Embodiments of the present disclosure can also be implemented in high-frequency bandwidths such as 70 GHz or above.

[0017] Figure 1 FIG. illustrates a block diagram of an example noise filter 100 in accordance with some embodiments of the present disclosure. The noise filter 100 can be, for example, a CTLE filter. The noise filter 100 includes an optional direct current (DC) block 102 configured to receive an input signal such as a signal from a device under test (not shown). For example, the DC block 102 can be configured to allow radio frequency (RF) signals to pass while blocking audio and DC frequency interference. The noise filter 100 may also include a splitter 104 to receive the output from the DC block 102 or, if the DC block 102 is omitted, to receive the input signal. The splitter 104 can be, for example, a Wilkinson splitter, which has a signal loss of 3 decibels (dB). However, embodiments of the present disclosure are not limited to such splitters, but can include any splitter that separates a signal into separate signals. In some instances, the splitter can be configured to separate the signal such that each separated signal substantially includes the entire bandwidth of the input signal. For example, another type of splitter that can be used is a three-resistor power splitter or a multiplexer.

[0018] The output of the splitter 104 is provided to two signal paths. The first signal path includes a fixed delay line 106. The second signal path includes a variable attenuator 108 and a variable delay line 110. In this example embodiment, the variable attenuator 108 and the variable delay line 110 are continuously variable. Although both the attenuator 108 and the delay line 110 are shown as continuously variable, embodiments are not limited to such a combination. Rather, only one of the attenuator 108 and the delay 110 may be viable. Other variations will be discussed below with respect to Figure 2-6This will be discussed in more detail. Additionally, the embodiments are not limited to the signal in the second signal path that is attenuated by the attenuator 108 before being delayed by the delay line 110. As those skilled in the art will understand, in some embodiments, although not shown, the signal in the second signal path may be delayed by the delay line 110 before being attenuated by the attenuator 108.

[0019] The variable attenuator 108 and / or the variable delay line 110 can be adjusted manually or by the controller 112. The controller 112 is shown, but the embodiments of the present disclosure are not limited to this implementation. More precisely, the variable attenuator 108 and / or the variable delay line 110 can be adjusted manually by the user.

[0020] The variable attenuator 108 can control the amplitude difference in dB between low frequencies and high frequencies. Adjusting the variable attenuator 108 does not move the pole positions of the entire noise filter 100. That is, the attenuator 108 only changes the height of the frequency response peak without shifting it in frequency. As such, it can be adjusted to accommodate different DUT channel losses for a given data rate. On the other hand, the variable delay line 110 moves the pole positions of the noise filter 100 in frequency without changing the range of the amplitude between high frequencies and low frequencies. As such, the variable delay line 110 can be adjusted to accommodate different data rate signals. That is, based on which channel of the test and measurement instrument receives the signal from the DUT, the variable attenuator 108 or the variable delay line 110 can be adjusted manually or by the controller, so that any noise added by that channel can be removed. For example, as will be discussed in more detail below, the user can determine the desired amount of attenuation and / or delay, and set the setting for the variable attenuator 108 or change the length of the delay line 110 to the desired amount. In other embodiments, the user may be able to set the desired amount on the test and measurement instrument, which then transmits instructions to the controller to adjust the variable attenuator 108 and / or the variable delay line 110. Additionally, in some embodiments, the test and measurement instrument may have specific attenuation amounts and / or delays stored in memory for each channel of the test and measurement instrument, and can direct the controller based on which channel the DUT is connected to.

[0021] The combiner 114 receives signals from both the first signal path and the second signal path, and combines the two signals together to obtain a negative branch sum. The combiner 114 should subtract the signals from the first signal path and the second signal path, or combine the signals from the first signal path and the second signal path when one path is inverted, to complete the negative branch sum. For example, in some embodiments, the combiner 114 may be a balun that includes an inverting input and a non-inverting input, which provides a desired shape for the noise filter frequency response. In some embodiments, the balun may be a 6 dB loss balun. As another example, in some embodiments, the combiner 114 may be an active differential amplifier that can operate down to zero frequency and provide gain.

[0022] The combined signal can be converted from an analog signal to a digital signal by the analog-to-digital converter 116. The digital signal can be stored in a memory or further processed in a test and measurement instrument. In some embodiments, a filter 118 may also be provided in the noise filter 100 to further filter the digital signal before the digital signal is stored in a memory or further processed by a test and measurement system such as an oscilloscope (not shown). The filter 118 may be a low-pass filter, a de-embed filter, and / or a reshaping filter. If a low-pass filter is used, the low-pass filter may limit the bandwidth of the digitized signal to only include the first slope and peak of the digital signal. For example, the noise filter 100 response may be sinusoidal in shape and only use the first slope. If a de-embed filter is used, the de-embed filter may reshape the frequency response of the test and measurement instrument channel back to a flat response. By doing so, the noise introduced by the noise filter 100 will be reduced without reducing the noise of the DUT. Finally, the attenuator 108 and / or the delay line 110 can be adjusted such that the output of the noise filter 100 is as close as possible to the desired response. If a reshaping filter is used, the reshaping filter further reshapes the output to the desired response. For example, a reshaping filter can be used whenever a test and measurement instrument channel is required to have a frequency response with a specific industry standard CTLE shape response.

[0023] The output of the ADC 116 or the filter 118 is substantially similar to the input signal, but the frequency attenuation caused by the test and measurement instrument channel has been removed by combining the signal in the first path that is delayed and attenuated based on the channel to which the DUT is connected to the test and instrument measurement, and the signal on the second path that is delayed by a known fixed delay.

[0024] Figure 2The figure shows a block diagram of another exemplary noise filter 200 in accordance with some embodiments of the present disclosure. Similar to Figure 1 , the noise filter 200 can include a DC block 102, a splitter 104, a fixed delay 106, a combiner 114, an ADC 116, and a filter 118, similar to those discussed above and their variations. Accordingly, these components will not be described in detail with respect to Figure 2 . As discussed below, the noise filter 200 provides a stepped control of the noise filter frequency response, rather than a continuous control as in the case of the noise filter 100 of Figure 1 .

[0025] Figure 2 The noise filter 200 of Figure 1 also includes a variable attenuator 202 and / or a variable delay line 210, similar to

[0026] . However, one or both of the variable attenuator 202 and / or the variable delay line 210 are composed of a plurality of fixed components that can be switched into or out of a second signal path. Figure 2 . For example, the variable attenuator 202 can include a plurality of fixed attenuators 204 that change the amount of attenuation. Although the fixed attenuators 204 list various attenuation amounts, this is shown for illustration only, and those skilled in the art will understand that the present disclosure is not limited to these specific fixed attenuator amounts. More precisely, the fixed attenuators 204 can have attenuation amounts different from those illustrated in

[0027] . A single-pole multi-throw switch 206 can be provided to switch the selected attenuation amount into the second signal path. The switch can be switched, can be manually switched by a user, or can be operated by a controller 112.

[0028] In some embodiments, the variable delay line 210 can also include a plurality of fixed delay lines 212 that change the amount of delay. A single-pole multi-throw switch 214 can be provided to switch the selected delay amount into the second signal path. Similar to the variable attenuator 202, the switch can be manually switched by a user or can be operated by the controller 112. In some embodiments, a separate controller 112 can be provided for each of the variable attenuator 202 and the variable delay line 210.

[0028] Although Figure 2Illustrated are both a variable attenuator 202 and a variable delay line 210 that include a plurality of fixed components and switches. However, in some embodiments, as will be appreciated by those skilled in the art, only one of the attenuator 200 and the delay line 210 includes fixed components and switches, and the other is a single fixed component or a variable attenuator 108 or variable delay line 110 as discussed above. That is, the variable attenuators 108 and 200 and the variable delay lines 110 and 210 can be provided in any combination, including a fixed delay line 110 and 210 or one of the attenuators 108 and 200.

[0029] In Figure 2 the illustrated embodiment, twelve possible frequency response settings are provided based on four fixed attenuators 204 and three fixed delay lines 212. However, the embodiments are not limited to such implementations. More precisely, any number of fixed attenuators 204 can be present and switched into the second signal path, and any number of fixed delay lines 212.

[0030] Figure 3 Illustrated is another exemplary noise filter 300 according to an embodiment of the present disclosure. Similar to Figure 1 and 2 , the noise filter 300 can include a splitter 104, a fixed delay 106, a controller 112, a combiner 114, an ADC 116, and a filter 118, similar to those discussed above and their variations. Accordingly, these components will not be described in detail with respect to Figure 3 here.

[0031] The noise filter 300 can include a multiplexer 302 to receive an input signal from a DUT. The multiplexer 302 is a passive device that implements frequency domain multiplexing. The multiplexer 302 can convert a signal with a wide frequency range, such as an input signal, into two or more signal bands with mutually exclusive frequency ranges. A multiplexer 302 that converts a signal into two frequency bands can be referred to as a diplexer, and a multiplexer that converts a signal into three frequency bands can be referred to as a triplexer, etc. For example, the multiplexer 302 is configured to split the input signal into a plurality of bands including a high frequency band and a low frequency band. Then the high frequency band and the low frequency band can be forwarded along a high frequency channel and a low frequency channel, respectively.

[0032] The low frequency band can be received at the splitter 102, similar to Figure 1 and Figure 2 discussed above. In Figure 3 the illustrated embodiment, the variable attenuator 108 and the variable delay line 110 are shown in the second signal path. However, the embodiments of the present disclosure are not limited to such implementations. As will be understood by those skilled in the art, the variable attenuator 202 and / or the variable delay line 210 can be provided in the second signal path, similar toFigure 2 The embodiments shown in

[0033] The multiplexer 304 receives the combined signal from the combiner 114. The multiplexer 304 acts as a combiner to combine the low-frequency band and the high-frequency band together into a full-bandwidth signal, which can be converted by the ADC 116 and filtered by the filter 118 (if any).

[0034] The multiplexers 302 and 304 have lower losses than the separator 102. For example, in the low-frequency band, the multiplexers 302 and 304 have losses of a few tenths of a decibel, and in the high-frequency band, they can have losses of 1.5 to 3 decibels, depending on how wide the bandwidth of the input signal is. Thus, when a significant portion of the loss is in the low-band frequencies of the input signal, the noise filter 300 may be beneficial. The noise filter 300 can be used to better shape the signal in the low-band frequencies to provide a better SNR, while allowing for lower losses in the high-band of the system to be captured with better resolution. Additionally, another advantage of the noise filter 300 is that the variable attenuator 108 or 202 and / or the variable delay line 110 or 210 operate only on half of the bandwidth of the system. For example, for a 50 GHz bandwidth system, the variable components only have to operate on a 25 GHz bandwidth.

[0035] Figure 4 Another example noise filter 400 according to some embodiments of the present disclosure is illustrated. The noise filter 400 can be used when receiving a differential signal pair from a DUT. The separator 402 (similar to the separator 102) receives the positive signal of the differential pair and separates it into a signal on the first positive signal path and a signal on the second positive signal path, while the separator 404 (also similar to the separator 102) receives the negative signal of the differential pair and separates it into a signal on the first negative signal path and a signal on the second negative signal path.

[0036] Both the first positive signal path and the first negative signal path include a fixed delay 106, as Figure 4 illustrated. Each of the second positive and negative signal paths includes a variable attenuator 108 or 202 and / or a variable delay line 110 or 210. Figure 4 The embodiments of Figure 2 illustrate the use of the variable attenuator 202 and the variable delay line 210, as discussed in detail above with respect to

[0037] The combiner 406 receives signals from the first positive signal path and the second negative signal path, and combines the signals into a first combined signal. The second combiner 408 receives signals from the second positive signal path and the first negative signal path, and combines the signals into a second combined signal. In such embodiments, since the positive and negative signals are combined, the combiners 406 and 408 can be, for example, power combiners. Then the first and second combined signals are received at the combiner 114, similar to that discussed above with respect to Figure 1 . The combiner 114 converts the first and second combined signals into a single differential signal output received by the ADC 116. That is, the noise filter 400 cross-couples the positive and negative signals using differential signal pairs to remove any attenuation from the test and measurement instrument channels.

[0038] Figure 5 The figure shows a block diagram of another exemplary noise filter 500 according to some embodiments of the present disclosure. The noise filter 500 is similar to the noise filter 400, except that there is no cross-coupling of the positive and negative signals of the differential signal pair as shown in Figure 4 . Accordingly, there is no further description of Figure 5 and Figure 4 and Figure 5 of the similar components. Instead of combining the two simple combiners 406 and 408 by cross-coupling the positive and negative signals, for example, two combiners 114 (baluns or differential amplifiers) as discussed above can be provided to couple each of the corresponding separate positive signals and the corresponding separate negative signals. Then the combined positive signals and the combined negative signals can be further combined by the combiner 502.

[0039] In addition, similar to Figure 4 , any combination of the variable attenuator 108 or 202 and the variable delay line 110 or 210 can be used, and one of the components therein is fixed.

[0040] As an alternative to the noise filter 500, a noise filter can be provided that is similar to that shown in Figure 5 but instead of combining the positive and negative branches into a single differential signal as shown in Figure 5 , the positive and negative signal paths can be processed separately by the corresponding ADC 116 and filter 118, and sent to the test and measurement instrument for further processing or stored in the memory as a differential signal pair, and not as a combined differential signal.

[0041] Figure 6The figure shows a block diagram of another example noise filter 600 for differential signals according to some embodiments of the present disclosure. In the noise filter 600, multiplexers 602 and 604 can be used to separate the positive and negative signals of a differential pair input signal into corresponding low-band frequency and high-band frequency signals. Both the positive low band and the positive high band are delayed by a fixed delay line 106. The negative low band and the negative high band are received at a path including a variable attenuator 108 or 202 and / or a variable delay line 110 or 210. Figure 6 Embodiments of which illustrate the use of variable attenuator 202 and variable delay line 210, as discussed above with respect to Figure 2 discussed in detail. However, as will be understood by those skilled in the art, any combination of variable attenuator 108 or 202 and variable delay line 110 or 210 can be used and one of the components therein is fixed.

[0042] The signals on the positive and negative low-frequency paths can be combined at combiner 606, and the signals on the positive and negative high-frequency paths can be combined at combiner 608 to output a combined low-band signal and a combined high-band signal. These signals can then be combined into a full-band combined signal by another multiplexer 610.

[0043] It will be appreciated that the multiplexer configuration can be implemented as Figure 1-Figure 3 a two-channel configuration of

[0044] The above-disclosed embodiments of the present disclosure provide a way to adjust the frequency response of a noise filter on a high-frequency bandwidth such as a bandwidth at 70 GHz or higher by having variable attenuators and / or variable delay lines in the signal path, which can then be subtracted from a reference signal to remove noise added by test and measurement instrument channels. Embodiments of the present disclosure allow a variable noise filter that can be programmed or set for a variety of different test scenarios, rather than having to switch in a new noise filter for each test scenario. Additionally, embodiments of the present disclosure allow adjustment of the settings of the noise filter to test specific criteria.

[0045] Aspects of the present disclosure may operate on specially created hardware, firmware, digital signal processors, or on specially programmed computers including processors operating according to programming instructions. The term controller or processor as used herein is intended to include microprocessors, microcomputers, application specific integrated circuits (ASICs), and dedicated hardware controllers. One or more aspects of the present disclosure may be embodied in computer-usable data and computer-executable instructions executed by one or more computers, including monitoring modules, or other devices, such as in one or more program modules. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. Computer-executable instructions may be stored on a computer-readable storage medium, such as a hard disk, optical disk, removable storage medium, solid state memory, random access memory (RAM), etc. As will be appreciated by those skilled in the art, in various aspects, the functionality of program modules may be combined or distributed as needed. Additionally, the functionality may be wholly or partially embodied in firmware or hardware equivalents, such as integrated circuits, FPGAs, etc. Particular data structures may be used to more efficiently implement one or more aspects of the present disclosure, and such data structures are contemplated within the scope of the computer-executable instructions and computer-usable data described herein.

[0046] In some cases, the disclosed aspects may be implemented in hardware, firmware, software, or any combination thereof. The disclosed aspects may also be implemented as instructions carried by or stored on one or more computer-readable storage media, which may be read and executed by one or more processors. Such instructions may be referred to as a computer program product. As discussed herein, computer-readable media means any media that can be accessed by a computing device. By way of example and not limitation, computer-readable media may include computer storage media and communication media.

[0047] Computer storage media means any media that can be used to store computer-readable information. By way of example and not limitation, computer storage media may include RAM, ROM, electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital video disc (DVD), or other optical disc storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, and any other volatile or non-volatile, removable or non-removable media implemented in any technology. Computer storage media does not include signals per se and transient signal transmission forms.

[0048] A communication medium means any medium that can be used for communication of computer-readable information. By way of example and not limitation, a communication medium can include coaxial cable, fiber optic cable, air, or any other medium suitable for communication of electrical, optical, radio frequency (RF), infrared, acoustic, or other types of signals.

[0049] Example

[0050] Illustrative examples of the technologies disclosed herein are provided below. Embodiments of the technologies can include any one or more of the examples described below and any combination thereof.

[0051] Example 1 A noise filter, comprising: a separator configured to receive a signal and separate the signal into at least a first separated signal and a second separated signal; a first path configured to receive the first separated signal, the first path including: a variable attenuator and a variable delay line; a second path configured to receive the second separated signal; and a combiner configured to combine the signal from the first path and the signal from the second path into a combined signal.

[0052] Example 2 is the noise filter of Example 1, wherein the second path includes a fixed delay line.

[0053] Example 3 is the noise filter of any one of Example 1 or 2, wherein at least one of the variable attenuator and the variable delay line is adjusted by a controller.

[0054] Example 4 is the noise filter of any one of Example 1 - 3, wherein the variable attenuator includes a plurality of attenuators, each attenuator having a different attenuation amount; and a plurality of switches, wherein the variable attenuator is adjusted by switching one of the plurality of attenuators to the first path.

[0055] Example 5 is the noise filter of any one of Example 1 - 4, wherein the variable delay line includes a plurality of delay lines, each delay line having a different delay amount; and a plurality of switches, wherein the variable delay line is adjusted by switching one of the plurality of delay lines to the first path.

[0056] Example 6 is the noise filter of any one of Example 1 - 5, wherein the combiner is a balun having an inverting input and a non-inverting input.

[0057] Example 7 is the noise filter of any one of Example 1 - 6, wherein the combiner is a differential amplifier.

[0058] Example 8 is a noise filter of any one of Examples 1-7, further comprising: a multiplexer configured to receive an input signal and separate the input signal into a high-band signal and a low-band signal, wherein the signal received by the separator is the low-band signal.

[0059] Example 9 is the noise filter of Example 8, wherein the multiplexer is a first multiplexer, and the combined signal is a first combined signal, and the noise filter further comprises: a second multiplexer configured to receive the first combined signal and the high-band signal and output a second combined signal.

[0060] Example 10 is a noise filter of any one of Examples 1-9, further comprising: an analog-to-digital converter configured to receive the combined signal and output a digital signal representing the combined signal; and a reshaping filter configured to receive the digital signal and output a filtered digital signal that matches a specific continuous-time linear equalizer shape response.

[0061] Example 11 is a noise filter, comprising: a first separator configured to receive the positive signal of a differential signal pair and separate the positive signal into at least a first separated signal and a second separated signal, each of the first and second separated signals substantially comprising the entire bandwidth of the positive signal; a second separator configured to receive the negative signal of the differential signal pair and separate the negative signal into at least a third separated signal and a fourth separated signal, each of the third and fourth separated signals substantially comprising the entire bandwidth of the negative signal; a first path configured to receive the first separated signal, the first path including a first variable attenuator and a first variable delay line; a second path configured to receive the second separated signal; a third path configured to receive the third separated signal, the third path including a second variable attenuator and a second variable delay line; a fourth path configured to receive the fourth separated signal; a first combiner configured to combine the signal from the first path and the signal from the fourth path into a first combined signal; a second combiner configured to combine the signal from the second path and the signal from the third path into a second combined signal; and a third combiner configured to combine the first combined signal and the second combined signal into a third combined signal.

[0062] Example 12 is the noise filter of Example 11, wherein the second path and the fourth path include fixed delay lines.

[0063] Example 13 is a noise filter of Example 11 or 12, wherein at least one of the first variable attenuator, the first variable delay line, the second variable attenuator, and the second variable delay line is adjusted by a controller.

[0064] Example 14 is a noise filter of any one of Examples 11 - 13, wherein at least one of the first variable attenuator and the second variable attenuator includes a plurality of attenuators, each attenuator having a different attenuation amount; and a plurality of switches, wherein at least one of the first variable attenuator and the second variable attenuator is adjusted by switching one of the plurality of attenuators to the first path.

[0065] Example 15 is a noise filter of any one of Examples 11 - 14, wherein at least one of the first variable delay line and the second variable delay includes a plurality of delay lines, each delay line having a different delay amount; and a plurality of switches, wherein at least one of the first variable delay line and the second variable delay is adjusted by switching one of the plurality of delay lines to the first path.

[0066] Example 16 is a noise filter of any one of Examples 11 - 15, wherein the third combiner is a balun having an inverting input and a non - inverting input.

[0067] Example 17 is a noise filter of any one of Examples 11 - 16, wherein at least one of the first combiner, the second combiner, and the third combiner is a multiplexer.

[0068] Example 18 is a noise filter of any one of Examples 11 - 17, further comprising: an analog - to - digital converter configured to receive the third combined signal and output a digital signal representing the third combined signal; and a filter configured to receive the digital signal and output a filtered digital signal.

[0069] Example 19 is a noise filter of any one of Examples 11 - 18, wherein each of the first and second separated signals substantially includes the entire bandwidth of the positive signal, and each of the third and fourth signals substantially includes the entire bandwidth of the negative signal.

[0070] Example 20 is a noise filter, including: a first multiplexer configured to receive a positive signal of a differential signal pair and separate the positive signal into a positive high-band signal and a positive low-band signal; a second multiplexer configured to receive a negative signal of the differential signal pair and separate the negative signal into a negative high-band signal and a negative low-band signal; a first path configured to receive the negative high-band signal, the first path including: a first variable attenuator and a first variable delay line; a second path configured to receive the positive high-band signal; a third path configured to receive the negative low-band signal, the third path including: a second variable attenuator and a second variable delay line; a fourth path configured to receive the negative low-band signal; a first combiner configured to combine a signal from the first path and a signal from the second path into a first combined signal; a second combiner configured to combine a signal from the third path and a signal from the fourth path into a second combined signal; and a third multiplexer configured to combine the first combined signal and the second combined signal into a third combined signal.

[0071] Example 21 is the noise filter of Example 20, wherein each of the second path and the fourth path includes a fixed delay line.

[0072] Example 22 is the noise filter of any one of Examples 20 or 21, wherein at least one of the first variable attenuator, the first variable delay line, the second variable attenuator, and the second variable delay line is adjusted by a controller.

[0073] Example 23 is the noise filter of any one of Examples 20-22, wherein at least one of the first variable attenuator and the second variable attenuator includes a plurality of attenuators, each attenuator having a different attenuation amount; and a plurality of switches, wherein at least one of the first variable attenuator and the second variable attenuator is adjusted by switching one of the plurality of attenuators to the first path.

[0074] Example 24 is the noise filter of any one of Examples 20-23, wherein at least one of the first variable delay line and the second variable delay includes a plurality of delay lines, each delay line having a different delay amount; and a plurality of switches, wherein at least one of the first variable delay line and the second variable delay is adjusted by switching one of the plurality of delay lines to the first path.

[0075] Example 25 is a noise filter of any one of Examples 20-24, further comprising: an analog-to-digital converter configured to receive the third combined signal and output a digital signal representing the third combined signal; and a filter configured to receive the digital signal and output a filtered digital signal.

[0076] Example 26 is a method comprising separating a signal into at least a first separated signal and a second separated signal, each of the first and second separated signals substantially comprising the entire bandwidth of the input signal; setting an attenuation amount for a variable attenuator; setting a delay amount for a variable delay line; attenuating the first separated signal by the attenuation amount through the variable attenuator; delaying the first attenuated separated signal by the delay amount through the variable delay line; and combining the delayed and attenuated first separated signal and the second separated signal into a combined signal.

[0077] Example 27 is the method of Example 26, further comprising delaying the second separated signal through a fixed delay line before combining the second separated signal and the delayed and attenuated first separated signal.

[0078] Example 28 is the method of any one of Examples 26 or 27, wherein setting the attenuation amount for the variable attenuator comprises switching in one of a plurality of different attenuators.

[0079] Example 29 is the method of any one of Examples 26-28, wherein setting the delay amount for the variable delay line comprises switching in one of a plurality of different delay lines.

[0080] Example 30 is the method of any one of Examples 26-29, wherein the signal is a first signal, and the method further comprises separating an input signal into a high-band signal and a low-band signal, wherein the first signal is the low-band signal.

[0081] Example 31 is the method of Example 30, wherein the combined signal is a first combined signal, and the method further comprises combining the first combined signal and the high-band signal into a second combined signal.

[0082] Example 32 is the method of any one of Examples 26-31, further comprising converting the combined signal into a digital signal representing the combined signal; and filtering the digital signal to reduce noise added by test and measurement instruments from the input signal.

[0083] Example 33 is a computer-readable storage medium having stored instructions that, when executed by one or more processors of a noise filter, cause the noise filter to separate a signal into at least a first separated signal and a second separated signal, each of the first and second separated signals substantially comprising the entire bandwidth of the input signal; set an attenuation amount for a variable attenuator; set a delay amount for a variable delay line; attenuate the first separated signal by the variable attenuator; delay the first separated signal by the variable delay line; and combine the delayed and attenuated first separated signal and the second separated signal into a combined signal.

[0084] Example 34 is the computer-readable storage medium of Example 33, wherein the instructions further cause the noise filter to delay the second separated signal by a fixed delay line before combining the second separated signal and the delayed and attenuated first separated signal.

[0085] Example 35 is the computer-readable storage medium of either Example 33 or 34, wherein setting the attenuation amount for the variable attenuator includes turning on one of a plurality of different attenuators.

[0086] Example 36 is the computer-readable storage medium of any one of Examples 33 - 35, wherein setting the delay amount for the variable delay line includes turning on one of a plurality of different delay lines.

[0087] The previously described versions of the disclosed subject matter have many advantages that have been described or will be apparent to one of ordinary skill in the art. Even so, these advantages or features are not required in all versions of the disclosed apparatus, system, or method.

[0088] In addition, this written description refers to specific features. It is to be understood that the disclosure in this specification includes all possible combinations of those specific features. Where a particular feature is disclosed in the context of a particular aspect or example, that feature can also be used, to the extent possible, in the context of other aspects and examples.

[0089] Moreover, when reference is made in this application to a method having two or more defined steps or operations, the defined steps or operations can be performed in any order or simultaneously, unless the context excludes those possibilities.

[0090] Although specific examples of the invention have been illustrated and described for purposes of illustration, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.

Claims

1. A noise filter for removing noise from a signal received from a device under test by a test and measurement instrument, wherein the noise is added to the signal by a specific channel of the test and measurement instrument, the noise filter comprising: A separator configured to receive a signal and separate the signal into at least a first separated signal and a second separated signal; A first path configured to receive the first separated signal, the first path including: A variable attenuator, and A variable delay line; A second path configured to receive the second separated signal; A combiner configured to combine the signal from the first path and the signal from the second path into a combined signal, An analog-to-digital converter configured to receive the combined signal and output a digital signal representing the combined signal; and A reshaping filter configured to receive the digital signal and output a filtered digital signal that matches a specific continuous-time linear equalizer shaped response, wherein at least one of the variable attenuator and the variable delay line is adjusted based on a specific channel of a test and measurement instrument.

2. The noise filter according to claim 1, wherein, The second path includes a fixed delay line.

3. The noise filter according to claim 1, wherein, At least one of the variable attenuator and the variable delay line is adjusted by a controller.

4. The noise filter according to claim 1, wherein, The variable attenuator includes: A plurality of attenuators, each attenuator having a different attenuation amount; and A plurality of switches, wherein the variable attenuator is adjusted by switching one of the plurality of attenuators to the first path.

5. The noise filter according to claim 1, wherein, The variable delay line includes: A plurality of delay lines, each delay line having a different delay amount; and A plurality of switches, wherein the variable delay line is adjusted by switching one of the plurality of delay lines to the first path.

6. The noise filter according to claim 1, wherein, The combiner is a balun having an inverting input and a non-inverting input.

7. The noise filter according to claim 1, wherein, The combiner is a differential amplifier.

8. The noise filter according to claim 1, further comprising: A multiplexer configured to receive an input signal and separate the input signal into a high-band signal and a low-band signal, wherein the signal received by the separator is the low-band signal.

9. The noise filter according to claim 8, wherein, The multiplexer is a first multiplexer, and the combined signal is a first combined signal, and the noise filter further includes a second multiplexer configured to receive the first combined signal and the high-band signal and output a second combined signal.

10. The noise filter according to claim 1, wherein, The signal is the positive signal of a differential signal pair, the separator is a first separator, the variable attenuator is a first variable attenuator, the variable delay line is a first variable delay line, the combiner is a first combiner, and the combined signal is a first combined signal, the noise filter further includes: A second separator configured to receive the negative signal of the differential signal pair and separate the negative signal into at least a third separated signal and a fourth separated signal; A third path configured to receive the third separated signal, the third path including: A second variable attenuator, and A second variable delay line; A fourth path configured to receive the fourth separated signal; A second combiner configured to combine the signal from the second path and the signal from the third path into a second combined signal; and A third combiner configured to combine the first combined signal and the second combined signal into a third combined signal.

11. The noise filter according to claim 10, wherein, The second path and the fourth path include fixed delay lines.

12. The noise filter according to claim 10, wherein, At least one of the first variable attenuator, the first variable delay line, the second variable attenuator, and the second variable delay line is adjusted by a controller.

13. The noise filter according to claim 10, wherein, At least one of the first variable attenuator and the second variable attenuator includes: A plurality of attenuators, each having a different attenuation amount; and A plurality of switches, wherein at least one of the first variable attenuator and the second variable attenuator is adjusted by switching one of the plurality of attenuators to the first path.

14. The noise filter according to claim 10, wherein, At least one of the first variable delay line and the second variable delay line includes: A plurality of delay lines, each having a different delay amount; and A plurality of switches, wherein at least one of the first variable delay line and the second variable delay line is adjusted by switching one of the plurality of delay lines to the first path.

15. The noise filter according to claim 10, wherein, The third combiner is a balun having an inverting input and a non-inverting input.

16. The noise filter according to claim 10, wherein, At least one of the first combiner, the second combiner, and the third combiner is a multiplexer.

17. The noise filter according to claim 10, further comprising: An analog-to-digital converter configured to receive the third combined signal and output a digital signal representing the third combined signal; and A filter configured to receive the digital signal and output a filtered digital signal.

18. The noise filter according to claim 10, wherein, Each of the first and second separated signals substantially includes the entire bandwidth of the positive signal, and each of the third and fourth separated signals substantially includes the entire bandwidth of the negative signal.

19. The noise filter according to claim 10, wherein, The first separator is a first multiplexer and the second separator is a second multiplexer, and wherein the first separated signal includes a first bandwidth of the positive signal and the second separated signal includes a second bandwidth of the positive signal, the first bandwidth and the second bandwidth being different from each other, and wherein the third separated signal includes a third bandwidth of the negative signal and the fourth separated signal includes a fourth bandwidth of the negative signal, the third bandwidth and the fourth bandwidth being different from each other.

20. A method for removing noise from a signal received by a test and measurement instrument from a device under test, wherein the noise is added to the signal by a specific channel of the test and measurement instrument, the method comprising: Separate a signal into at least a first separated signal and a second separated signal; Set the attenuation amount for the variable attenuator; Set the delay amount for the variable delay line; Attenuate the first separated signal passing through the variable attenuator by the attenuation amount; Delay the attenuated first separated signal passing through the variable delay line by the delay amount; Combine the delayed and attenuated first separated signal and the second separated signal into a combined signal; Receive the combined signal by an analog-to-digital converter and output a digital signal representing the combined signal; and Receive the digital signal by a reshaping filter and output a filtered digital signal that matches the shape response of a specific continuous-time linear equalizer, wherein at least one of the attenuation amount or the delay amount is set based on a specific channel of a test and measurement instrument.

21. The method according to claim 20, further comprising delaying the second separation signal through a fixed delay line before combining the second separation signal and the delayed and attenuated first separation signal.

22. The method according to claim 20, wherein setting the attenuation amount for the variable attenuator includes turning on one of a plurality of different attenuators, and / or wherein setting the delay amount for the variable delay line includes turning on one of a plurality of different delay lines.

23. The method according to claim 20, wherein The signal is a first signal, and the method further includes separating an input signal into a high-band signal and a low-band signal, wherein the first signal is the low-band signal, and wherein the combined signal is a first combined signal, and the method further includes combining the first combined signal and the high-band signal into a second combined signal.

24. The method according to claim 20, further comprising: Converting the combined signal into a digital signal representative of the combined signal; and Filtering the digital signal to reduce noise added by a test and measurement instrument from the signal.

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