The present invention relates to communications in general and in particular to transmission of signals capable of conveying information, wherein one or more of power consumption, pin-efficiency, SSO noise and common-mode noise are constraints.
One goal of a communication system may be to transport information from one physical location to another. In some electronic communication systems, the communication itself takes place between electronic components. For example, these electronic components may be integrated circuits (“ICs”) and this communication setting may be referred to as “chip-to-chip communication.” The communicating electronic components might be located in the same apparatus, such as the communication between a central processing unit (“CPU”) and memory inside a computer, tablet computing device, or other mobile device. Another example is the communication between two CPU cores that are integrated on the same chip. Yet another example is the communication between a Graphics Processing Unit (“GPU”) and memory on a graphics card. In these cases, the actual communication can take place over wires on a printed circuit board (“PCB”) and/or metal wires integrated in a chip and these wires carry electrical signals. It should be apparent upon reading this disclosure that other possibilities exist. The communication may, for instance, take place wirelessly or over an optical fiber.
In some cases, communication takes place between components that are located in different apparatuses. An example of this situation is a digital photo camera that is connected to a computer. In this setting, the communication can take place over a physical cable or wirelessly. Another example is a set of computers that are connected to a network. The electronic components on the network card of each computer may communicate with the electronic components of another network card of yet another computer.
In such communication settings, a goal may be to transmit digital information from one electronic component to another in a reliable and efficient way. The efficiency of the communication can be expressed in terms of the time it takes to transfer certain amount of information (speed), the energy that is required to transmit the information reliably (power consumption) and the number of wires per bit that is required for communication (pin-efficiency). Typically, several trade-offs exist between these parameters and, depending on the application, some of these parameters may be more important than others. One example is the communication between a CPU and a memory in a mobile device. A battery powers the mobile device and the power consumption of the communication between the CPU and memory can have a significant impact on the battery life. The desired trade-off may even change when the mobile device is connected to a non-portable power supply.
In some chip-to-chip communication systems communication takes place over a plurality of wires, for example, to increase the aggregate bandwidth. A single or pair of such wires may be referred to as a channel or link and multiple channels create a communication bus between the electronic components.
A difficulty in designing high speed, low power and pin-efficient chip-to-chip communication systems lies in part in the fact that the communication channel is not perfect. For example, the physical wires may disturb the signals transmitted on them and noise and interference may be added to the transmitted signals. As another example, the electronic components used to implement the communication system are not perfect and this can disturb the signals used for communication.
There can be multiple sources of noise in chip-to-chip communication systems. For example, there may be noise and interference that is common to a set of wires. This type of noise and interference is called common-mode noise. As another example, there may be thermal noise that is induced in electrical conductors. Thermal noise may be modeled as Gaussian noise that is added to each conductor independently. As yet another example, there may be simultaneous switching output (“SSO”) noise that is caused by a time-varying current in the electronics that drive the wires. As still another example, the signals transmitted on different wires may interfere with one other, which can cause crosstalk and significantly degrade signal integrity, especially at high speeds. As still yet another example, for some signaling methods an absolute voltage or current reference is required at the receiver. Such references are difficult to maintain with great precision and errors in the reference may cause unwanted distortions and noise.
Conventional attempts to combat the various types of noise while optimizing pin-efficiency and power consumption are inefficient, ineffective and/or have undesirable side effects or other drawbacks with respect to at least one significant use case.
Embodiments of the invention are directed toward solving these and other problems individually and collectively.
Methods and circuits for efficient processing and/or detection of balanced codes are enabled. A set of controlled sources may be placed in a configuration with one or more common nodes. One or more current sources may sink a predetermined current from each of the common nodes. A code word of a balanced code may be provided as inputs to the set of controlled sources, and a result may be derived from the current provided by each controlled source and/or from a fraction of the predetermined current provided by each controlled source. Alternatively, the circuit nodes associated with each of the controlled sources may be interconnected with an impedance. The controlled sources and/or the impedances may be configured with respect to the balanced code input.
Various embodiments in accordance with the present disclosure will be described with reference to the drawings, in which:
The attached figures provide examples that are further explained in the text below. Same numbers are used throughout the disclosure and figures to reference like components and features.
The subject matter of embodiments of the present invention is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described.
In accordance with at least one embodiment of the invention, methods and circuits for efficient processing and/or detection of balanced codes are enabled. Circuits that are matched to balanced codes may recover transmitted information in a noise resilient and power efficient manner. Circuit components for processing a balanced code may include one or more of: matched amplification of the signals representing the balanced code, matched equalization and/or filtering on the signals representing the balanced code, matched non-linear filtering on the signaling representing the balanced code to detect the presence of particular symbols and matched latching of the signals representing the balanced code. Such matched circuits and circuit components may be achieved at least in part by incorporating suitable common circuit nodes and/or a single energy source into circuit topologies.
In this disclosure the signaling methods disclosed in Cronie I, Cronie II and Cronie III are referred to as “balanced codes”. Balanced codes operate on three or more bus wires. A balanced code of length n has the property that the corresponding n signals transmitted on the bus satisfy
In Equation 1, si(t) denotes the signal present on the i-th bus wire. The signals may also sum to another predetermined number than 0 as is the case in Equation 1. In accordance with at least one embodiment of the invention, this predetermined number may be held constant for consecutive uses of the communication bus. Furthermore, after transmission across the wires of the bus, Equation 1 may only hold to a first approximation. Depending on the balanced code used, the signals transmitted on the wires of the bus may also satisfy additional constraints. For example, sparse signaling codes as introduced in Cronie II may result in a significant number of signals that are equal to 0. These additional properties may be used to implement power efficient receiver architectures as is shown in this disclosure.
A code word of a balanced code represents a set of information bits. One of the tasks of the receiver circuitry may be to recover these information bits. This recovery process may comprise several tasks such as amplification, equalization, analog-to-digital conversion, decoding and other suitable signaling processing. Collectively these processing steps are referred to herein as “processing a balanced code”. The operation of processing a balanced code may include one or more of: amplification of the signals representing the balanced code, performing equalization and/or filtering on the signals representing the balanced code, non-linear filtering on the signaling representing the balanced code to detect the presence of particular symbols and latching the signals representing the balanced code. It is often desirable to be able to perform several of these tasks in a power efficient way. In accordance with at least one embodiment of the invention, method and circuit techniques that are matched to balanced codes may recover the original information in a noise resilient and power efficient manner.
In accordance with at least one embodiment of the invention, the controlled sources 120 may incorporate one or more metal-oxide-silicon (MOS) transistors and/or bipolar transistors. Such transistors may be integrated in a chip (e.g., an integrated circuit or IC chip). In accordance with at least one embodiment of the invention, the controlled sources 120 may be implemented as a passive component such as a resistor or capacitor. In this case the controlled sources may comprise fewer terminals (e.g., two), as will be apparent to one of skill in the art familiar with resistors and capacitors.
Below, further aspects and/or details of processing units for balanced codes in accordance with at least one embodiment of the invention are described. For clarity, the above example of processing unit 100 is referenced consistently. However, processing unit 100 is not a limiting example. Processing units in accordance with at least one embodiment of the invention may implement one or more of: amplification for balanced codes, linear equalization for balanced codes, non-linear equalization for balanced codes, analog-to-digital conversion for balanced codes and decoding and detection of balanced codes.
Amplification for Balanced Codes
In accordance with at least one embodiment of the invention, a processing unit 100 may perform amplification of signals representing a word of a balanced code.
In accordance with at least one embodiment of the invention, the operation of the circuit 200 is such that this correspondence is linear to first approximation. Each of the currents in the branches 230 may flow through a resistor. This converts the current to a voltage and these voltages Vmax1, . . . , Vmax8 may correspond to the output of the circuit 200. In the circuit 200, common mode noise that is present on the inputs Vw1, . . . , Vw8 may be rejected. Since the input voltages correspond to a balanced code only a single tail current source 210 need be used. This can make the circuit 200 power efficient. Without significant modification the circuit 200 can be used to amplify four differential input signals and generate four differential output signals. Therefore, this circuit 200 can be used in multi-mode applications when the user wants to switch from one application to other ones. In accordance with at least one embodiment of the invention, the balanced code used is a sparse signaling code and may be the 8b8w code described in Cronie III. As will be apparent to one of skill in the art, the circuit 200 may easily be adapted to a different number of inputs and outputs.
In some cases it may be an advantage to implement the circuit of
In accordance with at least one embodiment of the invention, a circuit topology may be required to process a balanced code that provides more gain than the circuits depicted in
Each of the currents in the branches 430 flows through a resistor 450. One of the terminals of the resistors 450 is connected to the branches 430 and the other terminals are connected to a common-mode voltage VCM. This common-mode voltage may for example be equal to Vdd/2. The resistors 450 convert the current in the corresponding branch to a voltage and these voltages Vout1, . . . , Vout8 correspond to the output of the circuit. In the circuit 400, common-mode noise that is present on the inputs Vw1, . . . , Vw8 may be cancelled. Since the input voltages correspond to a balanced code only a single tail current source 411 is needed. This can make the circuit power efficient. The transconductance of PMOS transistors 421 may be configured to sum to the transconductance of the corresponding NMOS transistors 420 to increase the gain and also the bandwidth of the circuit. As will be apparent to one of skill in the art, the circuit 400 can be used to amplify four differential input signals and generate 4 differential output signals without significant modification. Therefore, this circuit can be used in multi-mode applications when the user wants to switch from one application to other ones. As will be apparent to one of skill in the art, the circuit may easily be adapted to a different number of inputs and outputs.
With technology scaling, the value of Vdd may be lowered and measures may need to be taken to operate the analog circuitry reliably.
Using such an RC network can enable several possibilities. For example, the DC bias at the gate of NMOS transistor 520 and PMOS transistor 521 may be changed such that the voltage headroom for these transistors is increased further. As another example, the RC network can provide frequency compensation and is useful for equalization. While in low frequencies 532 and 537 act as resistive dividers and hence change the DC bias voltage, at high frequencies, the parallel capacitors 532 and 537 show less impedance and will provide a boost at high frequencies. Furthermore, capacitors 532 and 537 can provide appropriate and independent DC operating conditions for the input transistors 520, 521.
Linear Equalization for Balanced Codes
The signals that represent a code word of a balanced code may be transmitted on wires that have a frequency selective transfer. In this case equalization circuitry may be required to reliable detect the information represented by the code word. For this purpose equalization circuitry may be used to compensate for the frequency selective channel transfer. In case a balanced code is used, power-efficient equalization circuitry can be designed. Several examples are described below.
An example circuit 700 that can be used for amplification and equalization is shown in
The common node 750 may be left floating since the input signals represent a code word of a balanced code. In the circuit 700, common-mode noise that is present on the input signals may be rejected. The circuit 700 may be relatively power efficient. Compared to the circuits in
In accordance with at least one embodiment of the invention, the transfer from input to output of the circuits exemplified in
In accordance with at least one embodiment of the invention, it is desirable to employ a complementary amplifier as described above with reference to
Non-Linear Equalization for Balanced Codes
In chip-to-chip communications, it may be desirable to be able to compensate for channel attenuation. In accordance with at least one embodiment of the invention, a decision feedback equalizer (DFE) may be incorporated into a suitable equalization architecture. A DFE is a non-linear equalizer that can exhibit a superior performance compared to linear equalizer architectures. For balanced codes, efficient circuit topologies may be derived using the property that the signals representing a code word of a balanced code sum to the same constant. An example DFE architecture is now further described with reference to
The coefficient c is chosen depending on the characteristics of the channel for which the DFE is designed. The currents steered into branches 952 are superimposed to the currents steered into branches 954. This performs the cancellation operation of the DFE. The resulting currents flow through resistor 930. The outputs of the circuit 900 include the voltages V1, . . . , V4. These voltages may be sampled and the balanced code may be decoded resulting a new decision for the next time slot.
In the DFE front-end of
Voltage-to-Time Conversion for Balanced Codes
In accordance with at least one embodiment of the invention, an analog-to-digital converter (ADC) may be employed to convert the signals that represent the code word of a balanced code to a digital representation. An architecture 1000 for an ADC that may exploit the properties of a balanced code is described with reference to
An example such VTC is now further described with reference to
Decoding and Detection for Balanced Codes
In accordance with at least one embodiment of the invention, a ternary balanced code is used. Examples of ternary balanced codes include the 4b5w code and the 8b8w code. The 4b5w code and 8b8w code are a type of balanced codes that are called sparse signaling codes. These codes are detailed in Cronie III. The code words of a sparse signaling code contain ‘1’ symbols, ‘−1’ symbols and ‘0’ symbols. To decode ternary sparse signaling codes one may employ an architecture that is based on finding the positions of the 1 symbols and −1 symbols only. For this purpose, max-detector circuits that may be employed to find the positions of the 1 symbols are described below. Furthermore, min-detector circuits that may be employed to find the positions of the −1 symbols are also described below.
An example max-detector circuit 1200 is now further described with reference to
The transistors of the circuit shown in
In accordance with at least one embodiment of the invention, it may be desirable for circuits to have a differential output.
Vout1=3Vin1−(Vin2+Vin3+Vin4) (Eqn. 2)
In case a balanced code is us used the sum of Vin2, . . . , Vin4 equals −3Vin1 and the differential output voltage Vout1 is proportional to Vin1. When the transistors 1310, 1320 operate in the linear regime the circuit 1300 of
The use of the circuitry 1300 described above is not limited to ternary balanced codes. Another example is provided by the binary balanced code of length 6 in which the code words are the 20 different permutations of the vector (+1,+1,+1,−1,−1,−1), or a suitable subset thereof. Here, when comparing 6 times the value of a coordinate position against the sum of the other coordinate positions, the resulting comparison will be the sign of the value of the given coordinate position. The circuitry in
Advantages of Processing Circuits for Balanced Codes
The circuits described above for processing of balanced codes provide multiple advantages. For example, the circuits for amplification and equalization provide resilience against common-mode noise that may be present on the input signals. The combination of the signals satisfying the balanced code property as given by Equation 1 and the presence of common nodes such as common node 130 of
As another example, the power consumption of the described circuits is relatively low. One reason for this is the presence of a common node 130 and a single source of energy 140. This single source of energy can take its form as a single or two current sources. For example, in
Balanced codes may also find their use in other applications besides chip-to-chip communications. Many of the methods and circuit techniques disclosed herein can provide similar advantages in these settings. An example is the application of balanced codes in the non-volatile storage of information as is described in Cronie IV. In accordance with at least one embodiment of the invention, the transistors 220 in
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and/or were set forth in its entirety herein.
The use of the terms “a” and “an” and “the” and similar referents in the specification and in the following claims are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “having,” “including,” “containing” and similar referents in the specification and in the following claims are to be construed as open-ended terms (e.g., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely indented to serve as a shorthand method of referring individually to each separate value inclusively falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation to the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to each embodiment of the present invention.
Preferred embodiments are described herein, including the best mode known to the inventors. Further embodiments can be envisioned by one of ordinary skill in the art after reading this disclosure. Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and subcombinations are useful and may be employed without reference to other features and subcombinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications can be made without departing from the scope of the claims below.
This application is a Continuation of and claims priority under 35 USC §120 to co-pending U.S. application Ser. No. 14/089,577, filed Nov. 25, 2013, which is a Continuation of U.S. application Ser. No. 13/542,599, now issued U.S. Pat. No. 8,593,305, filed Jul. 5, 2012, which is a non-provisional application claiming priority under 35 USC §119 to U.S. Provisional Application No. 61/504,676, entitled “Method and Circuits for Efficient Processing and Detection of Balanced Codes,” filed on Jul. 5, 2011, all of which are hereby incorporated herein by reference. The following references are additionally herein incorporated by reference in their entirety for all purposes: U.S. Patent Publication 2011/0268225 of application Ser. No. 12/784,414, filed May 20, 2010, naming Harm Cronie and Amin Shokrollahi, entitled “Orthogonal Differential Vector Signaling” (hereinafter “Cronie I”);U.S. Patent Publication 2011/0302478 of application Ser. No. 12/982,777, filed Dec. 30, 2010, naming Harm Cronie and Amin Shokrollahi, entitled “Power and Pin Efficient Chip-to-Chip Communications with Common-Mode Resilience and SSO Resilience” (hereinafter “Cronie II”);U.S. patent application Ser. No. 13/030,027, filed Feb. 17, 2011, naming Harm Cronie, Amin Shokrollahi and Armin Tajalli, entitled “Methods and Systems for Noise Resilient, Pin-Efficient and Low Power Communications with Sparse Signaling Codes” (hereinafter “Cronie III”); andU.S. patent application Ser. No. 13/464,849, filed on May 4, 2012, naming Harm Cronie and Amin Shokrollahi, entitled “Differential Vector Storage for Non-Volatile Memory” (hereinafter “Cronie IV”).
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Number | Date | Country | |
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61504676 | Jul 2011 | US |
Number | Date | Country | |
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Parent | 14089577 | Nov 2013 | US |
Child | 14956021 | US | |
Parent | 13542599 | Jul 2012 | US |
Child | 14089577 | US |