Patent Application
20180226983
The present disclosure relates generally to electronic circuitry, and more specifically to data converters.
A wireless device (e.g., a cellular phone or a smartphone) in a wireless communication system may transmit and receive data for two-way communication. In the process, the data signals communicated may be converted from an analog signal to a digital signal and vice versa. In a time-interleaved analog-to-digital converter (ADC), the signal-to-noise and distortion ratio (SNDR) determines the effective number of bits, and the spurious free dynamic range (SFDR) determines the dynamic range with consideration for spurs. For high performance systems with multiple sub-carriers, such as the orthogonal frequency division multiplexing (OFDM) family, spurs at a specific sub-carrier may cause high error rate at that sub-carrier. Therefore, for low error rates, low spurs are desired, resulting in stringent SFDR specifications. A time-interleaved ADC achieves a high sampling rate (fs) by interleaving N sub-ADC's. Unfortunately, the mismatches between sub-ADCs may cause spurs that reduce SFDR and SNDR, and decrease performance.
In an aspect of the present disclosure, a data converter is presented. The data converter includes multiple subunits to convert an input. The subunits are selected to sample the input in an order that varies over time. Two or more of the subunits are enabled at the same time.
In another aspect of the present disclosure, a method of data conversion is presented. The method includes simultaneously selecting multiple subunits to convert an input signal. The subunits are selected according to a variable hopping frequency. One of the subunits is enabled for calibration.
In yet another aspect of the present disclosure, a data converter is presented. The data converter includes means for simultaneously selecting multiple subunits to convert an input signal. The subunits are selected according to a variable hopping frequency. One of the subunits is enabled for calibration. The data converter further includes means for calibrating non-selected subunits during a period in which the selected subunits perform data conversion.
In yet still another aspect of the present disclosure, a wireless communication device is presented. The wireless communication device includes a data converter. The data converter includes multiple subunits that convert an input. The subunits are selected in an order that varies over time. Two or more of the subunits are enabled at the same time.
Additional features and advantages of the disclosure will be described below. It should be appreciated by those skilled in the art that this disclosure may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the teachings of the disclosure as set forth in the appended claims. The novel features, which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages, will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.
Aspects and features of the present disclosure will be more apparent by describing example aspects with reference to the accompanying drawings, in which:
While a number of inventive aspects are described herein, these aspects are presented by way of example only, and are not intended to limit the scope of protection. The apparatuses and methods described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions, and changes in the form of the example apparatuses and methods described herein may be made without departing from the scope of protection.
In accordance with aspects of the present disclosure, methods for mitigating time-interleaved ADC artifacts are presented. In one aspect, a sampling frequency hopping process achieves good SFDR, which is difficult to achieve with a time interleaving ADC. The hopping pattern may be based on a pseudorandom binary sequence (PRBS), for example. Based on the hopping pattern, a phase selector may be driven (e.g., via a finite state machine) to choose a specific sub-ADC. The ADC output samples may, in turn, follow a random order, so an output selector will sort them into the normal order. In another aspect, a finite state machine, for example, may drive the phase selector to choose a specific sub-ADC to sample the input and may drive a phase selector at the same phase to calibrate the unselected sub-ADC in the same time interval, resulting in SNDR improvement.
In yet another aspect of the present disclosure, a timing skew calibration process may be implemented to further improve performance. In one example, the output of a data converter channel under calibration may be measured at the highest slope. The output at the highest slope may be compared to an output of a reference channel. The difference between the outputs (e.g., the output of the channel being calibrated and the reference channel output) provides the sign of the timing skew. In turn, a finite state machine may be employed to converge to a correct trim code with a successive approximation process based on the sign of the timing skew.
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A mobile communication device 110 may communicate with the communication network 120 on a subscription 115 via the first eNodeB 122. For example, the mobile communication device 110 may transmit data to and receive data from the communication network 120 via the first eNodeB 122. A person having ordinary skill in the art can appreciate that the mobile communication device 110 may communicate with the communication network 120 on the subscription 115 via a different eNodeB (e.g., the second eNodeB 124) without departing from the scope of the present disclosure. Moreover, a person having ordinary skill in the art can appreciate that the mobile communication device 110 may communicate with different and/or additional communication networks on the subscription 115 and/or a different subscription without departing from the scope of the present disclosure.
The mobile communication device 110 may be any device capable of wirelessly communicating with one or more communication networks including, for example, but not limited to, the communication network 120. The mobile communication device 110 may be, for example, but not limited to, a smartphone, a tablet PC, or a laptop computer.
The SIM 240 may associate the communication unit 220 with the subscription 115 on the communication network 120. Although the mobile communication device 110 is shown to include a single SIM (e.g., the SIM 240), a person having ordinary skill in the art can appreciate that the mobile communication device 110 may include additional SIMs without departing from the scope of the present disclosure. The additional SIMs may associate the communication unit 220 with a different subscription on the communication network 120 or a different communication network.
The SIM 240 may be a universal integrated circuit card (UICC) that is configured with SIM and/or universal SIM (USIM) applications, enabling access to GSM and/or UMTS networks. The UICC may also provide storage for a phone book and other applications. Alternatively, in a CDMA network, a SIM may be a UICC removable user identity module (R-UIM) or a CDMA subscriber identity module (CSIM) on a card. A SIM card may have a central processing unit (CPU), read-only memory (ROM), random-access memory (RAM), electrically erasable programmable read-only memory (EEPROM) and input/output (I/O) circuits. An integrated circuit card identity (ICCID) SIM serial number may be printed on the SIM card for identification. However, a SIM may be implemented within a portion of memory of the mobile communication device 110, and thus need not be a separate or removable circuit, chip, or card.
The communication unit 220 may include an RF chain 230. The RF chain 230 may include, for example, but not limited to, an RF module 232 and an antenna 234. Although the mobile communication device 110 is shown to include a single communication unit (e.g., the communication unit 220), a person having ordinary skill in the art can appreciate that the mobile communication device 110 may include additional communication units without departing from the scope of the present disclosure.
The user interface 250 may include an input unit 252. The input unit 252 may be, for example, but not limited to, a keyboard or a touch screen. The user interface 250 may further include an output unit 254. The output unit 254 may be, for example, but not limited to, a liquid crystal display (LCD) or a light emitting diode (LED) display. A person having ordinary skill in the art will appreciate that other types or forms of input and output units may be used without departing from the scope of the present disclosure.
The control unit 210 may be configured to control the overall operation of the mobile communication device 110 including controlling the functions of the communication unit 220 including, for example, but not limited to, frequency synthesis performed by the RF module 232. The control unit 210 may be, for example, but not limited to, a microprocessor (e.g., general-purpose processor, baseband modem processor, etc.) or a microcontroller.
The storage unit 260 may be configured to store application programs, application data, and user data. At least some of the application programs stored at the storage unit 260 may be executed by the control unit 210 for the operation of the mobile communication device 110.
The wireless device 300 also includes multiple receive chains for receiving signals (e.g., radio frequency signals) to be processed by the wireless device 300 via the controller/data processor 314. For example, a first receive chain includes a first receive front end (RXFE) chain 330, a first analog to digital converter (ADC) 334, and a wireless transceiver (WTR) 332. A second receive chain includes a second receive front end (RXFE) chain 340, a second analog to digital converter (ADC) 344, and a wireless transceiver (WTR) 342. Each of the RXFEs (e.g., 330, 340) may include receive circuits (e.g., 336, 346) and input circuits (e.g., 338, 348). For data reception, an antenna (e.g., 234 of
In accordance with aspects of the present disclosure, the DACs (e.g., 304, 324) and the ADCs (e.g., 334, 344) may each be configured with multiple subunits. Each of the data converters (e.g., ADCs and DACs) may be configured to operate in accordance with a sampling frequency hopping process to improve the spurious free dynamic range of the wireless device 300. In some aspects, the hopping pattern may be based on a pseudorandom binary sequence (PRBS) or may be simply non-uniform, for example. Based on the hopping pattern, a phase selector may choose a specific sub-unit of the data converter. In some aspects, the phase selector choice may be driven by a finite state machine. In turn, the data converter may output samples that follow a random order. An output selector may then be used to sort the randomized output samples into a normal order.
In some aspects, the data converters (e.g., DACs (e.g., 304, 324) and the ADCs (e.g., 334, 344)) may also include one or more multi-phase clock generators coupled to each of the subunits separately to enable variable selectable clock phases.
where fs is the overall sampling rate, N is the total number of subunits, and D is a design parameter (e.g., degree of freedom that may be set to a value D≥1). Accordingly, the subunits may operate faster than conventional systems to enable non-uniform sampling.
The phase selection/calibration module 408 may generate a selection signal (e.g., psel<1:0>) to drive the phase selector 402 to select a subunit of the multiple subunits (e.g., 406) to perform a data conversion operation. The phase selection/calibration module 408 may generate a hopping frequency based, for example on a noise generator 412. In some aspects, the noise generator 412 may supply a non-periodic sequence. For example, the noise generator (e.g., pseudorandom number generator) may produce a pseudorandom binary sequence. Accordingly, the subunits may be operable according to a non-uniform timing. For instance, the subunits (e.g., 406) may be selected and may sample an input supplied by a multiplexor (MUX) 414 via a sampler 404 according to a hopping frequency that varies over time. The converted data signal may be output via an output module 410 and supplied to other components of a wireless communication device (e.g., WTR 322 of
In addition, a background calibration process may be applied to further improve performance. For example, non-selected subunits of the data converter may be subjected to calibration during the period in which the selected subunit is active. The phase selection/calibration module 408 may enable calibrations by sending an enable signal (cal_en) to a MUX 414. The phase selection/calibration module 408 sends a selection signal to the phase selector 402 to select an idle subunit for calibration. Further, the phase selection/calibration module 408 may compute an adjustment (e.g., gain or timing skew) for the idle subunit. The computed adjustment may be applied to the idle subunit according to the calibration tone (CAL tone).
The available subunits may be selected according to a non-uniform sequence. In some aspects, the selection may be random, such as based on a pseudorandom binary sequence (PRBS), for example. Each subunit has a sampling rate in the range of fs/3 and 0. That is, if a subunit is always selected, its sampling rate is fs/3 and if it is never selected, the subunit's sampling rate would be 0. In some aspects, the sampling rate may hop in the range set by these limits. Accordingly, the subunits may selectively sample the input in a non-uniform manner rather than at fixed or periodic intervals. For example, subunit 0 is selected at time steps 0T, 5T, and 8T. By implementing hopping in this manner, the tones or errors produced by the data converters (e.g., ADC) may be spread over a wide spectrum to improve SFDR performance.
The calibration module 720 corrects for gain errors. When a subunit (e.g., 702a-n) is selected for calibration (e.g., when idle), a start calibration signal (start_cal) is provided to the calibration module 720. An adjustment signal may be supplied to the phase select module 704. The phase select module 704 may select the subunit (e.g., 702a-n) for calibration based on the adjustment signal at a timing based on the master clock (mclk) supplied via the clock module 706, the synchronization clock (clkl), and the phase select signal (psel). The selected subunit for calibration may be designated via MUX 709. In this exemplary architecture, the synchronization clock clkl is generated by dividing the master clock mclk by N-D, where N is the number of subunits and D is a design parameter (e.g., N=4, D=1, so frequency of clkl is a third of the frequency of mclk). The divider 707 divides the master clock (Mclk) by an integer C (e.g., C=2, 12, 192) and sends a digital output calibration tone to the analog filter 710 to generate a differential analog calibration signal.
Table 1 below describes exemplary pseudocode for background calibration of the data conversion subunits. In the exemplary pseudocode, the gain and the timing skew are co-calibrated iteratively such that the timing skew and gain calibrations converge simultaneously, where N is the number of channels, P is the number of phases to measure, T is the number of timing skew trim bits, and the input calibration cosine wave frequency is fs/P.
Table 2 is a truth table for determining the selection signal via a decoder 810. The values included in the truth table are exemplary only and not limiting. If the two bit value psel<1:0>=p, then the clkout signal will rise after p rising edges of mclk. For instance, as shown in Table 2, if psel<1:0>=01 then the decoder 810 outputs s<2:0>=001 and the clkout signal will rise after 1 rising edge of mclk. If a subunit's clkout goes from low to high at time T, then the corresponding subunit is selected at time T.
At block 904, the process optionally calibrates the non-selected subunit enabled for calibration during the period in which the selected subunits perform the data conversion. In some aspects, the calibration includes a gain calibration process (e.g., the calibration process shown in Table 1). In other aspects, the calibration includes a timing skew calibration process (e.g., the calibration process shown in Table 1).
According to a further aspect of the present disclosure, a data converter is described. The data converter includes a means for simultaneously selecting multiple subunits to convert an input signal. The means for selecting may, for example, comprise the controller data processor 314, as shown in
In
The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the protection. For example, the example apparatuses, methods, and systems disclosed herein may be applied to multi-SIM wireless devices subscribing to multiple communication networks and/or communication technologies. The various components illustrated in the figures may be implemented as, for example, but not limited to, software and/or firmware on a processor, ASIC/FPGA/DSP, or dedicated hardware. Also, the features and attributes of the specific example aspects disclosed above may be combined in different ways to form additional aspects, all of which fall within the scope of the present disclosure.
The foregoing method descriptions and the process flow diagrams are provided merely as illustrative examples and are not intended to require or imply that the operations of the method must be performed in the order presented. Certain of the operations may be performed in various orders. Words such as “thereafter,” “then,” “next,” etc., are not intended to limit the order of the operations; these words are simply used to guide the reader through the description of the methods.
The various illustrative logical blocks, modules, circuits, and operations described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and operations have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.
The hardware used to implement the various illustrative logics, logical blocks, modules, and circuits described in connection with the various aspects disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but, in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of receiver devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. Alternatively, some operations or methods may be performed by circuitry that is specific to a given function.
In one or more exemplary aspects, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a non-transitory computer-readable storage medium or non-transitory processor-readable storage medium. The operations of a method or algorithm disclosed herein may be embodied in processor-executable instructions that may reside on a non-transitory computer-readable or processor-readable storage medium. Non-transitory computer-readable or processor-readable storage media may be any storage media that may be accessed by a computer or a processor. By way of example but not limitation, such non-transitory computer-readable or processor-readable storage media may include random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), FLASH memory, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of non-transitory computer-readable and processor-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and/or instructions on a non-transitory processor-readable storage medium and/or computer-readable storage medium, which may be incorporated into a computer program product.
Although the present disclosure provides certain example aspects and applications, other aspects that are apparent to those of ordinary skill in the art, including aspects which do not provide all of the features and advantages set forth herein, are also within the scope of this disclosure. Accordingly, the scope of the present disclosure is intended to be defined only by reference to the appended claims.
The present application claims the benefit of U.S. Provisional Patent Application No. 62/454,438, filed on Feb. 3, 2017, and titled “DATA CONVERTERS FOR MITIGATING TIME-INTERLEAVED ARTIFACTS,” the disclosure of which is expressly incorporated by reference herein in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62454438 | Feb 2017 | US |
