Adaptive Cable Equalizer

Abstract

To address signal degradation, a cable equalizer is provided that performs equalization using an equalizer integrated into the host module. [Solution] The cable equalizer is configured as part of the cable and comprises a first stage 208, a second stage 212, and a third stage 216. The first stage comprises a first stage bias voltage source 224 that provides a bias voltage to the first stage and a pre-emphasis module 228 that introduces pre-emphasis into the received signal to counteract the effects of signal amplification. The second stage comprises a buffer 242 that impedance matches with the first stage. The third stage comprises a bias current source 262 that generates a bias current and a tank equalizer circuit 260 that performs frequency-specific equalization on the second stage signal.

Description

[Technical Field]

[0001] 1. Field of the Invention The present invention relates to signal equalization, and in particular to a method and apparatus for signal equalization in a cable. [Background Art]

[0002] 2. Related Art As is understood in the art, signal equalization is an effective tool for counteracting the effects on a signal associated with passing through a channel. In some environments, it is necessary to connect electronic devices located only a short distance apart. Cables are often used to connect co-located devices. However, in many cases, signals passing through the cable result in unacceptable levels of signal degradation even when the cable is short. [Summary of the Invention] [Problem to be Solved by the Invention]

[0003] To address signal degradation, equalization can be implemented by an equalizer integrated in a host module. However, this is a complex and costly solution and may not be optimal in some cases because the properties or length of the cable may change, or the host may be connected without using a cable interconnect.

[0004] Another proposed solution is active copper cable equalization, which is incorporated into a cable, such as a twin-axial copper cable, to extend the reach of the cable. The additional reach is useful for saving cost in data center interconnections. The equalizer can be integrated on the paddle card in the cable module. Prior art systems have a number of drawbacks. One drawback of prior art cable-based equalizers is lack of linearity. The non-linearity of the equalizer cancels any equalization (pre-emphasis and de-emphasis) added at the host transmitter. In addition, prior art equalizers introduced an unacceptable amount of noise and increased the BER (bit error rate). [Means for solving the problem]

[0005] overview To overcome the shortcomings of prior art, a cable equalizer is disclosed. In one embodiment, the cable equalizer comprises a first stage, a second stage, and a third stage. The first stage comprises a first-stage bias current circuit configured to generate a bias current and a pre-emphasis module configured to introduce pre-emphasis into the received signal to counteract the effects of signal amplification. Part of the first stage is a bias voltage circuit configured to provide a bias voltage to the first stage. The second stage comprises a buffer configured to impedance match with the first stage. The third stage comprises a third-stage bias current circuit configured to generate a bias current. Part of the third stage comprises an equalizer circuit configured to perform frequency-specific equalization on the signal of the second stage and an amplifier configured to amplify the signal of the second stage. An output driver configured to output the amplified equalized signal from the third stage. To overcome the shortcomings of prior art, measures have been taken in the design to maintain high linearity and low noise. In one embodiment, the cable equalizer is configured to provide a 6-15 dB boost at the Nyquist frequency of 26.5625 GHz (100 G / lane) with high linearity and low noise.

[0006] In one embodiment, the cable equalizer further comprises a bias voltage circuit configured to provide bias voltages to the first and third stages. It is intended that the pre-emphasis module may comprise a diode-connected transistor in series with one or more resistors. The tank equalizer circuit may comprise two or more capacitors that can be switched to or out of the tank equalizer circuit in response to a control signal. In one configuration, the amplifier comprises a cascode common-emitter transistor pair and a cross-coupled capacitor. It is also intended that both the first-stage bias current circuit and the third-stage bias current circuit generate current based on a control signal that controls the bias current.

[0007] This specification also discloses a method for performing cable equalization, comprising receiving a signal that is being transmitted or will be transmitted through a cable, and performing pre-emphasis on the signal to counteract the effects of amplification to create a modulated signal. The modulated signal is then buffered by an intermediate stage to optimize return loss, and the buffered modulated signal is amplified and equalized in response to the effects on the signal passing through the cable.

[0008] In one embodiment, pre-emphasis processing counteracts frequency-specific effects of amplification. This method may further include generating one or more bias currents used to perform pre-emphasis and amplification, and may further include adjusting one or more bias currents to optimize cable equalization. In addition, the method may further include generating one or more equalization control signals used to adjust the capacitance of the equalizer to optimize cable equalization. Equalization can also be customized using one or more high-frequency control signals and one or more low-frequency control signals.

[0009] In another embodiment, a cable equalizer is disclosed, comprising a first stage including a pre-emphasis module configured to introduce pre-emphasis into the received signal to counteract the effects of signal amplification. A third stage is provided, comprising equalizer and amplifier circuits configured to perform frequency-specific equalization and amplification. A buffer is located between the first and second stages to minimize return losses between them.

[0010] In one embodiment, the pre-emphasis module comprises a diode-connected transistor in series with one or more resistors. The equalizer circuit comprises two or more capacitors that can be switched to or out of the tank equalizer circuit in response to a control signal. The amplifier circuit may comprise a cascode common-emitter transistor pair and a cross-coupled capacitor. The cable equalizer may further comprise a first-stage bias current circuit and a third-stage bias current circuit, both of which generate current based on a control signal that controls the bias current. In one embodiment, the buffer comprises an emitter follower pair. The buffer may be configured to shunt high-frequency signal components.

[0011] Other systems, methods, features, and advantages of the present invention will become apparent to those skilled in the art by examining the accompanying drawings and detailed description. All such additional systems, methods, features, and advantages are contained within this description, fall within the scope of the present invention, and are intended to be protected by the accompanying claims. [Brief explanation of the drawing]

[0012] Brief explanation of the drawing The components in the drawings are not necessarily proportional to the actual size; instead, the focus is on illustrating the principles of the present invention. In the drawings, similar reference numerals indicate corresponding parts in different figures. [Figure 1] This figure shows a block diagram and an exemplary embodiment of an adaptive cable equalizer. [Figure 2] This is an illustrative circuit diagram of a cable equalizer according to one embodiment. [Figure 3] Figure 2 is a circuit diagram of the equivalent circuit of the diode-connected transistor shown. [Figure 4] This figure shows an illustrative signal plot of the transfer functions of two circuit components. [Figure 5] This figure shows an exemplary tank equalizer that can be implemented according to the present invention. [Figure 6] This figure shows an exemplary ideal or theoretical transfer function from the equalizer input to the output, with each equalizer stage represented separately. [Figure 7] This figure shows exemplary plots of equalizer outputs for various equalizer control inputs. [Modes for carrying out the invention]

[0013] Detailed explanation Figure 1 shows a block diagram and an exemplary embodiment of an adaptive cable equalizer. In this exemplary embodiment, an input from a cable, etc., is connected to the equalizer 102 to provide a signal to the equalizer. The cable may include one or more cables, such as copper conductors, and the signal may include one or more signals passing through the cable. The input signal is provided to a first stage 108, which in this embodiment is configured to provide pre-emphasis to the received signal to compensate for subsequent stages and to impedance match the cable. The first stage 108 provides additional functions, which will be described later.

[0014] The second stage 112 is connected to the first stage and configured to perform buffering to interface with the first stage 108 and the third stage 116. The third stage 116 consists of amplification and equalization, as well as other functions. The output of the third stage is provided to an output 120 which may be for a cable or connector. The equalizer may be at one end of the cable or at both ends.

[0015] Figure 2 is an exemplary circuit diagram of a cable equalizer according to one embodiment. This is only one possible circuit embodiment, and it is intended that other circuit layouts are possible without departing from the scope of the appended claims. In addition, many of the circuit element groups are grouped by function within dashed boxes to aid in understanding and generalizing the configuration of the layout. As discussed herein, this configuration includes a first stage 208, a second stage 212, and a third stage 216.

[0016] As shown in the figure, input 204 is provided and configured to receive a signal from the cable. In series with each input path is an inductor 206, which is configured to decouple the circuit from the cable, improve input return loss, resonate the input capacitance of the diode-connected transistor 284 and the emitter follower stage, and also improve input impedance matching. Input 204 is connected to the first stage 208. Within the first stage 208 is a 55-ohm impedance matching resistor 220, which is configured to impedance match to 50 ohms when combined with a resistor in the pre-emphasis module 228. In other embodiments, other resistor values ​​may be used. Resistor 220 may also be referred to as a termination resistor.

[0017] The input path also connects to a bias circuit 224, which is configured to set and maintain a specified bias point (voltage) for the pre-emphasis module 228. In an embodiment, the bias circuit 224 includes a two-input operational amplifier. The pre-emphasis module 228 includes transistors connected as resistors and diodes as shown, to compensate for non-linearity in a subsequent stage such as the third stage 216 by generating inverse pre-distortion. When viewed from inside an integrated circuit, the diode-connected transistors 284 operate as a voltage divider between a source impedance and an input impedance. The diode-connected transistors 284 have their bases and collectors short-circuited, as a result of which the remaining terminals, namely the bases and emitters, are configured as diode terminals. The pre-emphasis module 228 is also connected to a variable bias current transistor 232 configured to establish and provide a first-stage bias current. The bias current can be adjusted to account for temperature, variation across processes, or any other factor. In this embodiment, the first-stage bias current source 232 has four different adjustable current settings for all the bias current sources 232, 244, 262 in each stage, but in other embodiments, a larger or smaller number of bias current levels may be established.

[0018] The variable bias current transistor 232 is part of a variable bias current mirror bank 236 that provides tail bias current to all three stages 208, 212, and 216. A bias bank control signal generator 238 provides a control signal to the variable bias current bank 236. The bias bank control signal generator 238 comprises two digital-to-analog converters (DACs) configured to convert a digital PTAT (proportional to absolute temperature) current from a bandgap reference generator and a digital calibration current into analog signals used to adjust and control the transistors 232, 244, 262 configured as current mirrors, and to control the current output of the transistors in the variable bias current bank 236. Inputs to the DACs may come from a memory, or may be stored or generated on-chip. The variable bias current bank 236 comprises devices for supplying bias current to each of the stages 208, 212, 216 through programmable transistors 232, 244, 262 as illustrated. By controlling the switches that control the inputs to the variable transistors 232, 244, 262, two current types can be mixed to achieve different temperature coefficients, which can ultimately be managed to reduce temperature variation of gain boost.

[0019] The pre-emphasis module 228 is configured to introduce pre-emphasis to the signal before amplification in the third stage 216, so as to counteract the frequency-dependent effect of amplification. Using pre-emphasis in an equalizer increases and maintains the linearity of the equalizer located at the third stage 216 when viewed from the input 204 to the output 240.

[0020] Referring here to the second stage 212, the signal path enters a buffer 242 in this embodiment, which includes a number of transistors, capacitors, inductors, and a pair of transistors 246 with a gain of 1. The transistors in buffer 246 are configured as an emitter follower pair 246, which helps maintain input return loss. The emitter follower pair 246 acts as a buffer between the first stage 208 and the third stage 216, and is configured to optimize input return loss, which would not be possible if the input stage were coupled to the output stage. The emitter follower pair 246 offers the advantages of being highly linear, low noise, and low power consumption. In this exemplary configuration, the signal in question is below 26 GHz, so above this frequency, the signal component is either noise or contained in noise and therefore unnecessary or undesirable and can be blocked. For this reason, amplification is performed up to 26 GHz, after which signal attenuation occurs and the noise is blocked. Buffer 242 (e.g., resistors, inductors, and capacitors) is configured such that at high frequencies, the capacitors short-circuit, shunting high-frequency signal components away from the next stage, thereby maintaining a low noise level.

[0021] The second-stage bias current source 244 supplies bias current to the buffer. The bias bank control signal generator 238, as configured in the first stage 208, supplies bias current to the second-stage bias current source 24 The second-stage bias current source 244 generates a control signal that is supplied to 4. The second-stage bias current source 244 has a switch associated with it to control which of two or more control signals is connected to the base of transistor 224. In this embodiment, one control signal is temperature-based or temperature-responsive, and the other control signal is based on or response to tests and measurements that occur during calibration.

[0022] The upper compartment of the second stage 212 contains a voltage generator 248 configured to supply voltage to the first stage bias voltage source 224. The voltage generator 248 includes a programmable or variable resistor that allows the output voltage to be adjusted to account for variations in manufacturing variables and processes. Once set to a desired level, it generally remains fixed during operation. Within the voltage generator 248 are a current source 252 and a variable resistor 250 that can be used to adjust the voltage to a desired level.

[0023] Referring here to the third stage 216, the signal path is connected to an amplifier 254 with a gain greater than 1 in this embodiment. The amplifier is formed by a pair of cascode common-emitter transistors 252 coupled to a switchable degenerate tank and a cross-coupled capacitor 256. The term degenerate indicates that the tank attenuates all or part of the signal. The gain of the third stage 216 can be directly expressed as follows:

[0024]

number

[0025] In the formula, Y tank This is tank admittance. The third stage 216 acts as the main programmable equalizer and final driver from the integrated circuit. Although not shown, off-chip AC coupling capacitors may be required to block DC bias from the host transmitter and receiver. Amplifier 254 is configured with a gain greater than 1, but it is desirable to suppress common-mode gain to avoid differential imbalance and undesirable resonance. To reduce common-mode gain, degenerate resistors and inductors are used in the emitter follower stage (second stage 212) and the common-emitter stage (third stage 216), respectively. To further reduce the common-mode gain of the common-emitter (third stage), a tank equalizer 260 may be placed inside a p-well and connected to global GND through a large impedance.

[0026] The gate-collector connection of the cross-coupled capacitor 256 to the main differential pair cancels out undesirable capacitance at the base of the third-stage transistor 252, thereby increasing the bandwidth of the third-stage transistor 216.

[0027] Below the amplifier 254 is a tank equalizer 260, which is configured as a tank equalizer circuit. The tank equalizer 260 will be described in more detail below in relation to Figure 5.

[0028] The tank equalizer 260 performs equalization on the signal and functions as a low-pass filter, with the passband blocked at frequencies above the relevant signal frequency, which in this embodiment is 26 GHz. The tank equalizer 260 is connected to an inductor and a third-stage bias current source transistor 262, which is part of a bias current source bank 236. The third-stage bias current source transistor 262 is variable and can be switched between two inputs shown, which are from a bias bank control signal generator 238.

[0029] The tank equalizer 260 receives an input from a voltage source 264 that provides the tank equalizer 260 with a desired voltage, which in this embodiment is 1.8 volts generated by a resistor network from a 3.3-volt source. In this embodiment, the tank transistor utilizes a 1.8-volt power supply. However, in other embodiments, the tank equalizer 260 may utilize a different voltage.

[0030] Furthermore, the equalization control signal source 28 provides input to the tank equalizer 260. The equalization control signal source 268 provides two control signals, which in this embodiment are a low-frequency bit control signal and a high-frequency bit control signal. The high-frequency bits are from the lookup table (LUT) 270. Lookup table calculations are used to compensate for variations between parts and different cable lengths. In addition, different lookup tables can be stored in memory to accommodate a wider range of environments and cable lengths / types. The use of the low-frequency bit control signal and the high-frequency bit control signal will be discussed in more detail below in relation to Figure 5.

[0031] Above amplifier 254 is an output driver (or output stage) 272, which includes an equalizer output 240. The output driver 272 receives the equalized amplified signal from amplifier 254. The output driver 272 includes a transistor 274 with a base terminal connected to a bias voltage source 248 found in the second stage 212. An inductor 276, which functions to block undesirable high-frequency signal components and noise from the output port 240, connects the output driver 272 to amplifier 254. The output driver 272 includes a supply voltage connected through an output impedance matching resistor 280.

[0032] Figure 3 shows the schematic of the equivalent circuit of the pre-emphasis module 228 shown in Figure 2. The input termination diode pair 228 in Figure 3 can be represented as a circuit having an input 304 connected in parallel to two resistors 308, 312, with one branch of a parallel-connected resistor having diode 316. The output Vo 320 is also shown. Diode 316 represents the diode-connected transistor shown in Figure 2. The equivalent resistors 308, 312 set the input impedance to match the transmission line input impedance represented as a 50-ohm resistor 324.

[0033] Figure 4 shows an exemplary signal plot of the transfer functions of two circuit components. The vertical axis 404 represents the transconductance (g mThe horizontal axis 408 represents the voltage Vd across the diode-connected transistor 284 in Figure 2. The diode-connected transistor transfer function plot 412 shows that at high Vd voltages the pre-emphasis module 228 (Figure 2) allows the signal to pass through, and at low Vd voltages the pre-emphasis module attenuates the signal.

[0034] Conversely, the third-stage transfer function plot 416 shows that at high Vd voltages, the third stage 216 (Figure 2) attenuates the signal, while at low Vd voltages, the third stage does not attenuate the signal. The Rd plot 412 shows the transfer function of the resistance of the first stage 208 generated from the diode-connected transistor 284. m Plot 416 represents the third-stage transfer function. By multiplying or combining these two circuit transfer functions, the result is a more linear transfer function from input to output. In this way, the combined transfer function can resemble plot 420, thereby the first stage 208 provides pre-emphasis to compensate the third stage 216 in order to maintain linearity across the equalizer from input to output.

[0035] Figure 5 shows an exemplary tank equalizer 260 that can be implemented by this technological innovation. The circuit in Figure 5 is an exemplary representation of the tank equalizer 260 of Figure 2. However, it is intended that other equalizer circuits that do not depart from the scope of the appended claims may be used. In this embodiment, the tank equalizer 260 controls bias current It includes a lower terminal 504 connected to the power source and an upper terminal 508 connected to the amplifier 254 shown in Figure 2. An inductor 550 is in series with the lower terminal 504, and at very high frequencies the inductor appears as an open circuit, so the inductor 550 makes the resistor in the RL branch insignificant or as if it were not in the circuit at high frequencies. As a result, the inductor 550 maintains the input impedance of the tank equalizer 260 at high frequencies.

[0036] Internally, the tank equalizer 260 has three equalization branches 520, 524, and 528, which may each have one or more sub-branches. One of the branches includes an RL branch 520, which is configured with a resistor as shown. The RL branch 520 includes a resistor and an inductor as shown. The RL branch 520 is configured to attenuate signal frequencies beyond the target frequency range. In this embodiment, all three equalization branches 520, 524, and 528 are connected in parallel.

[0037] The second equalization branch is referred to herein as a high-frequency equalization branch 524 configured to equalize the high-frequency components of the signal. The high-frequency equalization branch 524 receives a control signal on a high-frequency control signal path 530. The control signal is supplied to a resistor 544, which is connected to a branch containing a plurality of capacitors 536. Between the plurality of capacitors 536 is a switching transistor 540 configured to enable or disable one or more of the above-mentioned branches of the high-frequency equalization branch 524 in response to the control signal. Thus, the above-mentioned branches are either part of the circuit or excluded from the circuit (on or off), thereby adjusting the capacitance of the tank equalizer 260. In this embodiment, there are eight high-frequency control signals on the control signal path 530 and eight sub-branches within the high-frequency equalization branch 524. In other embodiments, more or fewer sub-branches may be configured. During operation, the high-frequency equalization branch 524 is controlled to selectively filter the high-frequency components of the signal.

[0038] Furthermore, part of the equalizer is a low-frequency equalization branch 528 that receives low-frequency control signals on the low-frequency control signal path 534. The low-frequency equalization branch 528 is configured similarly to the high-frequency equalization branch 524, but also includes a capacitor and a resistor in series. For DC or low-frequency signal contents, the capacitor appears as an open circuit, while at high frequencies, the capacitor appears as a short circuit, and the resistor remains the dominant element in the low-frequency equalization branch. The low-frequency control signals are supplied on the low-frequency control signal path 534, which in this embodiment includes three control signals, each supplied to one of the three sub-branches of the low-frequency equalization branch 528. The operation of the low-frequency equalization branch 528 is similar to that of the high-frequency equalization branch 524.

[0039] The tank equalizer 260 is implemented by an RL branch in parallel with multiple RC and C branches, which may be controlled by a switch that is an NMOS device. The RL branch 520 sets the DC gain by providing low-frequency emitter degeneracy. Eight RC branches 528 control the gain in the low-frequency range (up to 10 GHz), while three C branches 524 are for the high-frequency range up to the Nyquist frequency of 26.5 GHz. Parasitic elements present in the actual implementation of the RC and C branches 523, 528 dramatically reduce admittance in the higher frequency range. Therefore, at high frequencies, the admittance of the tank equalizer 260 is determined by the RL branch 520, thereby helping the inductor 550 reduce the admittance of the branch. A low overall admittance of the tank equalizer 260 results in greater degeneracy and smaller gain boost. A steep roll-off above the Nyquist frequency is preferable to reduce the integrated noise of the equalizer. As used herein, the term "integrated noise" is defined to mean noise that is integrated or accumulated over frequency and introduced in association with each element of the circuit. This noise reduction is achieved without consuming the extra power conventionally used to reduce noise.

[0040] The switch sizes (transistors 540, 558) are scaled proportionally to the sizes of the capacitors 636, 560 for each branch 524, 528. Furthermore, to reduce the capacitance of the body diodes, the control signals are connected to the drain and source terminals of the switches (transistors) 540, 558, while the gates are connected to a 1.8-volt supply. The frequency response of the tank equalizer 260 is critical to the equalizer performance, and as a result, all routing parasitic interferences are minimized and accurately modeled. Additionally, the MIM (metal, insulator, metal) capacitors are divided into slices and tiled to establish the shortest paths.

[0041] Using three branches and dynamically controllable control signals, the tank equalizer 260 may be tuned to selectively pass and block specific frequencies in order to adjust the frequency response to counteract channel influences. Equalizer tuning may also be performed in conjunction with the first-stage pre-emphasis behavior to optimize operation in order to maintain a linear transfer function as needed in the target frequency band.

[0042] To calibrate the frequency response of the tank equalizer 260 across process variations, the RC time constant of each integrated circuit is measured during automated testing at the time of manufacture. This measurement is based on the frequency of a test voltage-controlled oscillator that has a replica tank RC as a delay stage. After calibration, the tank selection control signal (bit) is adjusted to obtain a constant frequency response independent of the process corner. Furthermore, the emitter follower (second stage 212) and equalizer bias current are calibrated by the replica bias circuit to ensure consistent gain across the process corner.

[0043] Figure 6 shows an exemplary ideal or theoretical transfer function from the equalizer input to the output, with each equalizer stage represented separately. This is only one possible equalizer transfer function plot, and establishing different equalizer transfer functions is within the scope of this invention. The vertical axis 604 represents 20log(|Y|), which can be thought of as the signal magnitude or attenuation level. The horizontal axis 608 represents the logarithmic frequency in log(f).

[0044] The RL transfer function plot 620 represents the transfer function of the RL branch 520 (Figure 5) of the tank equalizer 260. As shown in the RL transfer function plot 620, the transfer function of the RL branch 520 is flat, meaning that, for example, it does not cause attenuation at low frequencies, but actively attenuates the signal beyond the target signal frequency range, which in one embodiment may be 25.6 GHz. This prevents high-frequency signal noise from undesiringly affecting the signal.

[0045] The high-frequency branch transfer function plot 624 represents the transfer function of the high-frequency branch 524 (Figure 5) of the tank equalizer 260. As shown in the high-frequency branch transfer function plot 624, the transfer function of the high-frequency branch of the tank equalizer 260 results in less attenuation at higher frequencies than at lower frequencies. At low frequencies, the high-frequency branch of the tank equalizer 260 may appear as an open circuit due to the behavior of the capacitor, while at high frequencies, the capacitor 536 (Figure 5) appears as a short circuit.

[0046] The low-frequency branch transfer function plot 628 represents the transfer function of the low-frequency branch 528 (Figure 5) of the tank equalizer 260. As shown in the low-frequency branch transfer function plot 628, the transfer function of the low-frequency branch of the tank equalizer 260 results in less attenuation at higher frequencies than at lower frequencies. At low frequencies, it may appear as an open circuit due to the behavior of the capacitor. At medium frequencies, the resistor in the low-frequency branch 528 causes the transfer function to transition almost flat, and then at high frequencies, the capacitor in the low-frequency branch 528 (Figure 5) appears as a short circuit, thereby establishing less attenuation at high frequencies.

[0047] The overall transfer function plot 632 shows the combined transfer function of the three plots, which is the overall transfer function of the tank equalizer 260. As can be seen from the figure, this is generally a high-pass filter with a flat frequency response at intermediate frequencies.

[0048] Figure 7 shows exemplary plots of the equalizer output for various equalizer control inputs. These are just one possible set of transfer function plots showing various equalizer performance results. As shown, the vertical axis 704 represents the output signal power as a function of frequency, shown on the horizontal axis 708. Various plots 712 are unfolded during testing of designs implemented using this technique and show the various frequency behaviors of the equalizer resulting from switching in and out of different sub-branches of the equalizer, which result in different tank equalizer 260 settings. As mentioned above, these plots were created by turning the eight switches of the high-frequency branch 524 (Figure 5) on and off and sweeping the gain boost as shown in Figure 5. It is clear that the operation of these switches (transistors) mainly affects the high-frequency bandwidth boost, changing the 26 GHz gain from 6.1 dB to 16 dB with a step size of less than 0.2 dB. In other embodiments, other frequencies and gain levels may be established.

[0049] The technological innovations described herein offer numerous advantages. One improvement is the increased linearity achieved by using pre-emphasis in the first stage to counteract the nonlinearity of the third-stage amplifier. While the third-stage amplifier is made as linear as possible, all amplifiers inherently possess some degree of nonlinearity, especially as the amplifier input signal increases. Therefore, the first stage counteracts this drawback and improves the overall linearity from cable input to cable output. Maintaining cable linearity is crucial for the operation of the entire system environment.

[0050] Although various embodiments of the present invention have been described, it will be apparent to those skilled in the art that many more embodiments and configurations are possible within the scope of the invention. Furthermore, the various features, elements, and embodiments described herein may be claimed or combined in any combination or configuration.

Claims

1. A cable equalizer that is configured as part of a cable, A pre-distortion module configured to introduce pre-distortion into the received signal to counteract the effects of subsequent processing. A pre-strain stage equipped with, It is the output stage, An equalizer circuit configured to perform frequency-specific amplification on the output stage signal, An output driver configured to perform impedance matching with the aforementioned cable and output an equalization signal from the output stage to the aforementioned cable, It includes an output stage, A buffer configured to impedance match the pre-distortion stage and the output stage, A cable equalizer equipped with [feature name].

2. The cable equalizer according to claim 1, further comprising a bias voltage circuit configured to provide a bias voltage to the pre-distortion stage and the output stage.

3. The cable equalizer according to claim 1, wherein the pre-distortion module comprises one or more resistors and a diode-connected transistor in series.

4. The cable equalizer according to claim 1, wherein the equalizer circuit comprises two or more capacitors that can be switched to or from the tank equalizer circuit in response to a control signal.

5. The cable equalizer according to claim 1, wherein the equalizer circuit comprises a cascode common emitter transistor pair and a cross-coupled capacitor.

6. The cable equalizer according to claim 1, further comprising a pre-distortion stage bias current circuit and an output stage bias current circuit, both of which generate a bias current based on a control signal that controls the bias current.

7. A method for implementing cable equalization, Receiving signals that are being transmitted or will be transmitted via a cable, To counteract the effects of amplification, pre-distortion processing is applied to the signal to create a modulated signal. In order to optimize the return loss, the modulated signal is buffered by an intermediate stage, In order to counteract the influence on the signal passing through the cable, the modulated signal after buffering is equalized. Methods that include...

8. The method according to claim 7, wherein the pre-distortion treatment counteracts the frequency-specific effects of amplification.

9. The method according to claim 7, further comprising generating one or more bias currents to bias a circuit that provides a bias current for performing pre-distortion and amplification, and further comprising adjusting at least one of the one or more bias currents to optimize cable equalization.

10. The method according to claim 7, further comprising generating one or more amplification control signals used to adjust capacitance to optimize cable equalization.

11. The method according to claim 7, further comprising customizing amplification based on one or more high-frequency control signals and one or more low-frequency control signals.

12. A pre-distortion stage comprising a pre-distortion module configured to introduce pre-distortion into the received signal to counteract the effects of the output stage, The output stage includes an equalizer circuit configured to perform frequency-specific amplification, A buffer between the pre-strain stage and the output stage to minimize the return loss between the pre-strain stage and the output stage. A cable equalizer equipped with [feature name].

13. The cable equalizer according to claim 12, wherein the pre-distortion module comprises one or more transistors and a diode-connected transistor in series.

14. The cable equalizer according to claim 12, wherein the equalizer circuit comprises two or more capacitors that can be switched to or from the tank equalizer circuit in response to a control signal.

15. The cable equalizer according to claim 12, wherein the equalizer circuit comprises a cascode common emitter transistor pair and a cross-coupled capacitor.

16. The cable equalizer according to claim 12, further comprising one or more bias current circuits configured to generate a bias current based on a control signal that controls the bias current.

17. The cable equalizer according to claim 12, wherein the buffer comprises an emitter follower pair.

18. The cable equalizer according to claim 12, wherein the buffer is configured to shunt high-frequency signal components.

19. The cable equalizer according to claim 12, wherein the output stage is further configured to perform output impedance matching.

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