The present invention generally relates to high speed serial links, and, more particularly, to compensation circuits utilized in the receiving end of the high speed serial link.
High speed serial links are common in modern electronic devices which, for example, use Serial Advanced Technology Attachment (SATA), Peripheral Component Interconnect (PCI)-Express (PCIe) or Universal Serial Bus (USB) interfaces to transmit data. Due to the imperfect transmission channel (i.e., inevitable channel losses), signals usually attenuate during transmission. In view of this, the receiving end of the high speed serial link needs to compensate the received signal to obtain a better eye diagram. The better the quality of the eye diagram, the better the performance of the electronic device.
However, channel losses are usually frequency-dependent (i.e., losses are different from frequency to frequency); therefore, to provide a channel loss compensation circuit (which can also be referred to as an equalizer in some applications) that can flexibly adjust the gain-frequency relationship (i.e., the alternate current (AC) response, which can be regarded as the compensation characteristic of the channel loss compensation circuit) has become an important issue in this technical field.
In view of the issues of the prior art, an object of the present invention is to provide a channel loss compensation circuit, so as to make an improvement to the prior art.
According to one aspect of the present invention, a channel loss compensation circuit is provided. The channel loss compensation circuit is utilized in a receiving end of an electronic device and includes a load, a first transistor, a second transistor, a first current source, a second current source, an adjustable capacitor, and an adjustable resistor. The first transistor has a first terminal, a second terminal, and a third terminal. The first terminal receives an input signal, and the second terminal is coupled to a power supply voltage through the load. The second transistor has a fourth terminal, a fifth terminal, and a sixth terminal. The fourth terminal receives the input signal, and the fifth terminal is coupled to the power supply voltage through the load. The first current source is coupled between the third terminal and a reference voltage. The second current source is coupled between the sixth terminal and the reference voltage. The adjustable capacitor is coupled between the third terminal and the sixth terminal. The adjustable resistor is coupled between the third terminal and the sixth terminal.
According to another aspect of the present invention, a channel loss compensation circuit is provided. The channel loss compensation circuit is utilized in a receiving end of an electronic device and includes a load, a first transistor, a second transistor, a first current source, a second current source, a capacitor array, and a resistor array. The first transistor has a first terminal, a second terminal, and a third terminal. The first terminal receives an input signal, and the second terminal is coupled to a power supply voltage through the load. The second transistor has a fourth terminal, a fifth terminal, and a sixth terminal. The fourth terminal receives the input signal, and the fifth terminal is coupled to the power supply voltage through the load. The first current source is coupled between the third terminal and a reference voltage. The second current source is coupled between the sixth terminal and the reference voltage. The capacitor array is coupled between the third terminal and the sixth terminal and includes a plurality of capacitors and a plurality of first switches. The resistor array is coupled between the third terminal and the sixth terminal and includes a plurality of resistors and a plurality of second switches. An equivalent capacitance of the capacitor array is related to the number of the first switches that are turned on, and an equivalent resistance of the resistor array is related to the number of the second switches that are turned on.
These and other objectives of the present invention no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiments with reference to the various figures and drawings.
The following description is written by referring to terms of this technical field. If any term is defined in this specification, such term should be interpreted accordingly. In addition, the connection between objects or events in the below-described embodiments can be direct or indirect provided that these embodiments are practicable under such connection. Said “indirect” means that an intermediate object or a physical space exists between the objects, or an intermediate event or a time interval exists between the events.
The disclosure herein includes channel loss compensation circuits. On account of that some or all elements of the channel loss compensation circuits could be known, the detail of such elements is omitted provided that such detail has little to do with the features of this disclosure, and that this omission nowhere dissatisfies the specification and enablement requirements. A person having ordinary skill in the art can choose components equivalent to those described in this specification to carry out the present invention, which means that the scope of this invention is not limited to the embodiments in the specification.
The transistor M1 and transistor M2 are embodied by N-type Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) (hereinafter referred to as NMOS transistors). The gate of the transistor M1 receives the input signal Vip, the drain of the transistor M1 is coupled to the power supply voltage VDD through the resistor Ra of the load 110, and the source of the transistor M1 is coupled to the reference voltage (e.g., ground) through the current source 120. The gate of the transistor M2 receives the input signal Vin, the drain of the transistor M2 is coupled to the power supply voltage VDD through the resistor Ra′ of the load 110, and the source of the transistor M2 is coupled to the reference voltage through the current source 125. The gate of the transistor M1 and the gate of the transistor M2 together form the input terminals of the channel loss compensation circuit 100, and the input signal Vip and the input signal Vin together form a differential input signal Vi. The channel loss compensation circuit 100 compensates the differential input signal Vi and generates a differential output signal Vo, which comprises the output signal Vop and the output signal Von. The drain of the transistor M1 and the drain of the transistor M2 together form the output terminals of the channel loss compensation circuit 100. The output signal Vop is outputted from the drain of the transistor M1, and the output signal Von is outputted from the drain of the transistor M2. The drain of the transistor M1 and the drain of the transistor M2 are respectively coupled to the ground through the load capacitors CL. The load capacitors CL are the load of the channel loss compensation circuit 100 and do not belong to the channel loss compensation circuit 100.
The capacitor array 130, coupled between the source of the transistor M1 and the source of the transistor M2, includes multiple capacitors (C1 to Cm, m>1) and multiple switches (S1a to Sma and S1a′ to Sma′). The switch Spa and the switch Spa′ form a switch pair (1≤p≤m, that is, the capacitor array 130 includes m switch pairs). One end of the capacitor Cp is coupled to the source of the transistor M1 through the switch Spa, and the other end of the capacitor Cp is coupled to the source of the transistor M2 through the switch Spa′. The switches S1a to Sma and the switches S1a′ to Sma′ are controlled by the control signal Ctrl1. In other words, the number of capacitors in the capacitor array 130 that are actually connected in parallel (i.e., the number of capacitors that are connected as a result of the switch pairs electrically connected thereto being turned on) can be controlled by the control signal Ctrl1. In other words, the equivalent capacitance of the capacitor array 130 is controlled by the control signal Ctrl1. The capacitance of the capacitors C1 to Cm can be any value. In some embodiments, the control signal Ctrl1 controls at least one switch pair to be turned on.
The resistor array 140, coupled between the source of the transistor M1 and the source of the transistor M2, includes multiple resistors (R1 to Rn, n>1) and multiple switches (S1b to Snb and S1b′ to Snb′). The switch Sqb and the switch Sqb′ form a switch pair (1≤q≤n, that is, the resistor array 140 includes n switch pairs). One end of the resistor Rq is coupled to the source of the transistor M1 through the switch Sqb, and the other end of the resistor Rq is coupled to the source of the transistor M2 through the switch Sqb′. The switches S1b to Snb and the switches S1b′ to Snb′ are controlled by the control signal Ctrl2. In other words, the number of resistors in the resistor array 140 that are actually connected in parallel (i.e., the number of resistors that are connected as a result of the switch pairs electrically connected thereto being turned on) can be controlled by the control signal Ctrl2. In other words, the equivalent resistance of the resistor array 140 is controlled by the control signal Ctrl2. The resistance of the resistors R1 to Rn can be any value. In some embodiments, the control signal Ctrl2 controls at least one switch pair to be turned on.
In some embodiments, the switches S1a to Sma, the switches S1a′ to Sma′, the switches S1b to Snb, and the switches S1b′ to Snb′ are embodied by transistors, and the control signal Ctrl1 and the control signal Ctrl2 are digital signals. For example, the control signal Ctrl1 includes m bits, each bit corresponding to a switch pair (including the switch Spa and the switch Spa′), and the control signal Ctrl2 includes n bits, each bit corresponding to a switch pair (including the switch Sqb and the switch Sqb′). The control signal Ctrl1 and the control signal Ctrl2 can be generated by the baseband processor of the electronic device (such as a central processing unit (CPU), micro controller, micro processor, digital signal processor (DSP), or their equivalents). In some embodiments, the baseband processor generates the control signal Ctrl1 and the control signal Ctrl2 according to the AC response of the differential input signal Vi.
Since the positions of the zero point ωz1 and the pole ωp1 are related to the equivalent capacitance of the capacitor array 130 and the equivalent resistance of the resistor array 140, the positions of the zero point ωz1 and the pole ωp1 can be changed (i.e., adjusting the compensation characteristics of the channel loss compensation circuit 100) by the control signal Ctrl1 and/or the control signal Ctrl2. For example, please refer to
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In summary, the channel loss compensation circuit of the present invention can flexibly adjust the compensation characteristics (i.e., the relationship between the gain and the frequency), and its effects include a smaller jitter in the eye diagram and the obtaining of the convergence point of the better minimum edge of the eye diagram. The channel loss compensation circuit of the present invention can improve the eye diagram of the receiving end of the high speed serial link, which, in other words, can improve the performance of the receiving end of the high speed serial link.
The transistors in the embodiments discussed above are not limited to the NMOS transistors, and people having ordinary skill in the art can replace the NMOS transistors with P-type metal-oxide-semiconductor (PMOS) field-effect transistors based on the above discussions. The channel loss compensation circuit of the present invention can also be utilized in the managed switches conforming to the XSGMII/TGR specification.
The shape, size, and ratio of any element in the disclosed figures are exemplary for understanding, not for limiting the scope of this invention.
The aforementioned descriptions represent merely the preferred embodiments of the present invention, without any intention to limit the scope of the present invention thereto. Various equivalent changes, alterations, or modifications based on the claims of the present invention are all consequently viewed as being embraced by the scope of the present invention.
Number | Date | Country | Kind |
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110108142 | Mar 2021 | TW | national |