With the accession of the NI agent arresting transceiver (VST), National Instruments redefines chart by bringing the adaptability of user-programmable FPGAs to RF instrumentation.
The NI Agent Arresting Transceiver (VST) ancestors combines RF I/O functionality begin in acceptable box appearance agent arresting analyzers (VSAs) and agent arresting generators (VSGs) forth with user-defined functionality to apparatus arresting processing and ascendancy all central a field-programmable aboideau arrangement (FPGA). The RF ascribe and RF achievement both accept absolute bounded oscillators (LOs), abundance advantage from 65 MHz to 6 GHz, and absolute bandwidth of up to 200 MHz. The VST is a distinct 3 or 4 aperture PXI Express bore (see Amount 1 below). Assorted Input, Assorted Achievement (MIMO) configurations can additionally be created by appliance several VST modules in a distinct PXI Express chassis.
Figure 1: NI PXIe-5644R/45R/46R Accouterments Avant-garde Panel
What’s so acute about the NI PXIe VST family? The aerial achievement that is attainable in such a baby footprint. Through avant-garde arrangement and wideband agenda correction, NI’s VST bandage achieves the achievement expectations of R&D-grade chart while advancement an abundantly baby anatomy factor. Coupling bunched chart with faster analysis times and adaptability from the user-programmable FPGA makes the VST alluringly ill-fitted for RF characterization, verification, validation, and assembly test.
While aerial functionality in a baby brand is impressive, the best advocate affection of the VST ancestors is the user-programmable FPGA. The Xilinx Virtex-6 FPGA, which is programmable with the NI LabVIEW FPGA Module, is affiliated to the VSA and VSG baseband I/Q data, as able-bodied as 24 agenda I/O curve with a abstracts amount of up to 250 Mbit/s. This able aggregate of RF, accelerated agenda I/O, and FPGA technologies gives the VST the adeptness to abode a avant-garde array of applications such as real-time accessory beneath analysis (DUT) control, custom triggering, power-level servoing, software authentic radio, approach emulation, and abounding others.
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The VST ancestors FPGA basecard consists of a Xilinx Virtex-6 FPGA, baseband clocking circuitry, analog-to-digital converters (ADCs), digital-to-analog converters (DACs), a programmable action agenda I/O bandage (PFI 0), agenda I/O connector, PCI Express interface, PXI triggers, DRAM, and SRAM.
Figure 2: Block Diagram of the VST Basecard
The NI PXIe-5644R/45R contains a Xilinx Virtex-6 LX195T FPGA and the NI PXIe-5646R utilizes the Xilinx Virtex-6 LX240T. The Xilinx Virtex-6 FPGAs are acclimated for arrangement configuration, agenda abstracts movement, and agenda arresting processing. The onboard FPGA has absolute admission to the ADCs, DACs, PCI Express bus, DRAM, SRAM, PFI 0, agenda I/O, and PXI triggers, acceptance for custom programming to accommodated the needs of abounding types of applications.
The Xilinx Virtex-6 LX195T and the LX240T FPGAs accept the afterward resources.
Experienced and amateur users in acceptable FPGA architectonics can productively administer the adeptness of reconfigurable accouterments through use of the LabVIEW FPGA Module. The LabVIEW development environment, congenital on the archetype of abstracts breeze and parallelism, is able-bodied ill-fitted to accompaniment the inherent accommodation of reconfigurable accouterments design. The LabVIEW FPGA Bore provides users the adeptness to absolutely affairs the Xilinx FPGA present in the VST family.
National Instruments provides LabVIEW sample projects appliance the Apparatus Architectonics Library (IDL) API for the VST acceptance users to alpha utilizing their accouterments for analysis and development immediately. The IDL VIs accommodate the user admission to adapt LabVIEW cipher at both the FPGA and processor levels. Archetype IDL VIs are categorized according to function, such as configuration, acquisition, generation, agenda arresting processing (DSP), and synchronization (see Amount 3 below). To apprentice added about the software of the VST, apprehend the VST Software Architectonics white cardboard or watch the VST webcast.
Figure 3: LabVIEW Sample Project and Apparatus Architectonics VI Mapping to VST Hardware
The VST has assorted clocks central the onboard FPGA. The capital alarm is the sample clock, acclimated to alarm the ADCs, DACs, and their accompanying FPGA logic.
The sample alarm runs at 120 MHz and 250 MHz for the NI PXIe-5644R/45R and 5646R, respectively, with a absolutely selectable source. Users can baddest the onboard Temperature Controlled Oscillator (TCXO), REF IN avant-garde console connector, or PXI_CLK 10 as the advertence arresting for the Appearance Lock Bend (PLL). Although the sample alarm abundance is anchored at 120 MHz with the 5644R/45R or 250 MHz with the 5646R, high-resolution I/Q abstracts ante can be able appliance the Fractional Interpolation and Fractional Decimation DSP VIs central the FPGA.
Figure 4: VST Clocking Architecture
The afterward table lists the clocks in the FPGA. In accession to these clocks, LabVIEW FPGA allows for acquired clocks at user-defined frequencies.
The VST uses dual-channel, 16-bit ADCs and DACs while the NI PXIe-5646R makes use of 14-bit ADCs and 16-bit DACs to accomplish faster abstracts rates. The ADCs and DACs are clocked at 120 MS/s to accommodate 80 MHz of circuitous bandwidth for the 5644R/45R and 250 MS/s to accommodate 200 MHz of circuitous bandwidth for the 5646R. All VST ADCs and DACs are automatically synchronized to the sample alarm area central the FPGA, which enables deterministic cessation amid accept and transmit. The RF IN and RF OUT IQ abstracts streams are calmly in the aforementioned FPGA alarm area authoritative programming easier acceptance synchronization and deterministic cessation for real-time analysis and anchored applications.
PFI 0 is a 3.3 v LVTTL, bidirectional, general-purpose agenda I/O signal. The best accepted use of PFI 0 is as a activate ascribe or a marker/event output. However, because the PFI 0 I/O absorber is affiliated anon to the FPGA, its functionality can be programmed for custom applications appliance LabVIEW FPGA.
The agenda I/O on the VST is attainable via a VHCDI port. There are 24 bidirectional LVTTL agenda I/O lines, configurable per port, with four curve per anchorage (six ports total). The agenda I/O adapter contains the Alarm In and Alarm Out lines, as able-bodied as PFI 1 and PFI 2 curve that can be acclimated for triggering or added bidirectional agenda I/O. The agenda I/O buffers are affiliated anon to the FPGA, acceptance the functionality of the alone agenda I/O signals to be programmed for custom applications appliance LabVIEW FPGA.
National Instruments offers several cables and accessories that are accordant with the agenda I/O connector. Note that these cables and accessories use a custom pinout that matches the VST agenda I/O and advance the 50 ohm manual bandage environment. The use of added VHDCI cables is not recommended.
The NI PXIe-5644R/45R has two banks of DRAM with 256 MB per coffer and a abstract best abstracts amount of 2.1 GB/s per bank; anniversary coffer is apart attainable from the FPGA. These DRAM banks are accepted purpose, but are generally acclimated for autumn waveforms to be generated or waveforms that accept been acquired.
The NI PXIe-5646R has two banks of DRAM with 512 MB per coffer for a absolute of 1 GB and a abstract best abstracts amount of 2.1 GB/s per bank. The banks are addressable as 512 MB blocks appliance the NI-RFSA and NI-RFSG disciplinarian sets, area anniversary 512 MB block is aloof for Tx and Rx tasks. The Apparatus Architectonics Library disciplinarian set provides the added functionality of acclamation the absolute DRAM as 1GB to be activated by a distinct Tx or Rx task.
Every affiliate in the VST ancestors has 2 MB of onboard SRAM with a best apprehend abstracts amount of 40 MB/s and address abstracts amount of 36 MB/s. SRAM is accepted purpose memory, which is generally acclimated for autumn assorted accouterments configurations that can be activated anon from the FPGA after action from the host.
The VST has a PCI Express, Gen 1 x4 backplane connection, which is acclimated for DMA transfers, programmed I/O, and peer-to-peer streaming.
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The VST ancestors appearance a dyne RF receiver, additionally accepted as a synchrodyne, zero-IF (ZIF), or direct-down about-face receiver. In a dyne receiver, the admission RF arresting is fed into a abundance mixer aloof like in a acceptable heterodyne receiver. However clashing a heterodyne receiver, the abundance of the LO in a dyne receiver is identical to, or actual aing to, the abundance of the admission RF signal, consistent in a DC-centered or low IF arresting such as 10 or 20 MHz.
The ascribe arresting is alloyed bottomward to baseband and breach into in-phase (I) and quadrature-phase (Q) components, area the carrier is in-phase and account by 90 degrees respectively. The I and Q aisle signals are again alone digitized consistent in I and Q data. Finally, the I and Q abstracts streams are accumulated in software, apprehension the aboriginal signal. Amount 5 shows a simplified block diagram of a dyne, or zero-IF architecture.
Figure 5: Homodyne (Zero-IF) Architectonics Basic Block Diagram
The dyne architectonics boasts a cardinal of advantages over the acceptable heterodyne architectonics including simpler design, lower cost, beneath adeptness consumption, and aerial selectivity, which allows break of adjoining channels whose signals overlap. Added advantages accommodate college abeyant bandwidths, simpler designs with distinct LOs, and a abate brand due to a added bunched design. These advantages are declared in added detail below.
1. Bandwidth. Receivers with distinct ADCs accept a activated aerial absolute for arresting bandwidth of 40 percent of the sample alarm frequency. With the aforementioned sample alarm frequency, dyne architectures acquiesce bifold the bandwidth, or 80 percent of the sample alarm frequency, because two ADCs are used. In general, ADCs with lower acceptable sample alarm frequencies accept bigger spurious-free activating ambit (SFDR) and signal-to-noise arrangement (SNR) performance. Homodyne receivers acquiesce added bandwidths after the accommodation in ADC achievement that is a all-important accommodation of distinct ADC receivers.
2. Distinct LO. With multichannel altitude systems acceptable added important for assorted input, assorted achievement (MIMO) applications, administration the LO is a requirement. With alone one LO to allotment in a dyne architectonics as against to assorted LOs in a acceptable heterodyne architecture, dyne architectures become a added cost-effective and beneath complicated arrangement to configure.
3. Bunched Design. Homodyne architectures accept abundant simpler RF designs over heterodyne architectures. Beneath LO signals; no bulky, big-ticket RF and IF filters; and beneath about-face stages for the dyne architectonics accomplish for a added bunched design.
Although the advantages are numerous, the dyne architectonics does appear with its own set of challenges, such as the disability to apparatus envelope detection. The VST overcomes this botheration by appliance quadrature apprehension and agenda arresting processing.
DC offsets are accession claiming of a zero-IF architecture. Any arresting that mixes bottomward to 0 Hz in the ZIF anatomy causes a ashen basic at DC. This baloney avalanche at the centermost of the absolute bandwidth of the abstracts acquisition. A spectrum composed of pasted calm abstracts acquisitions, anniversary account in abundance by the absolute bandwidth, will appearance this DC account appellation replicated in the centermost of anniversary abstracts acquisition. Nulling of the DC account is able on the digitized I and Q abstracts streams by applying offsets. A abstracted nulling action charge be activated for anniversary LO frequency, which is done automatically by active the VST self-calibration procedure.
The high-level architectonics of the VST receiver architectonics is apparent in Amount 6. This diagram highlights the arrangement synthesizer, alternative attenuators for aerial power, alternative amplifiers for low adeptness signals, out of bandage baddest filters, added accretion and abrasion arresting conditioning, and demodulation over one of three mixers depending on frequency.
Figure 6: VST Receiver Block Diagram
The baddest clarify coffer has eight altered paths with lowpass or bandpass filters. These filters aish abundant of the exceptionable noise, absorption alone on the arresting ambit of interest. After implementing the selectable clarify and applying some added arresting conditioning, the RF arresting is again beatific to one of three demodulators, depending on the signal’s frequency. Anniversary demodulator operates aural a specific abundance bandage to optimize accretion and appearance arresting integrity.
The receiver aisle includes several solid accompaniment attenuators that accommodate added than 80 dB of attenuation, capricious in 1 dB steps. The RF ascribe is AC-coupled. There are three switchable accretion amplifiers and a preamplifier to extend activating ambit and advance the system’s babble figure.
A low appearance babble LO is supplied internally to affix assorted downconverters with a distinct LO source. Appliance the aforementioned LO antecedent is advantageous for phase-coherent arresting accretion applications, such as assorted input, assorted achievement (MIMO) systems. Appliance this agreement ensures every RF channel, administration the accepted LO, is acquainted to the aforementioned RF frequency.
The downconverted baseband arresting is anon transmitted to the centralized ADC channels of the VST. The ADC channels digitize the baseband analog arresting and avenue the aftereffect to the onboard FPGA for added processing, and again alteration to the host. The NI PXIe-5644R/45R and 5646R ADCs digitize the baseband analog arresting at 120 MS/s over a 16-bit activating ambit and 250 MS/s over a 14-bit activating ambit respectively.
The VST receiver appearance a single-stage, absolute about-face (I/Q) downconverter. The RF arresting is downconverted from the configured LO abundance to DC, area the baseband arresting can be digitized for processing. This architectonics allows for avant-garde absolute bandwidth with aerial angel aishment and basal LO leakage. Angel aishment and LO arising achievement is able by wideband quadrature correction. The receiver aisle is optimized to be acclimated as a agent arresting analyzer for wideband demodulation.
A low IF receiver is accession blazon of receiver that uses an IQ demodulator, area the block diagram is identical to the zero-IF receiver apparent in Amount 5. Clashing in the zero-IF receiver area the LO abundance is positioned to be aural the abundance ambit of the articulate signal, in the low IF receiver the LO abundance is placed alfresco of the articulate arresting range. The aftereffect is that the DC basic is no best aural the downconverted span. Abounding of the impairments associated with the DC appellation such as DC offset, 1/f noise, and in some cases baseband accord are no best an issue.
Any user can amalgamate the capabilities of LO affability and agenda abundance alive to accomplish the VST in low IF mode. Acquiring or breeding the arresting of absorption at a digitally confused abundance from the carrier avoids the implications of LO arising present in absolute about-face topology. The accommodation is the best BW of the low IF receiver is bisected that of the zero-IF receiver accustomed identical ADC sample rates. The NI PXIe-5644R/45R supports up to 80 MHz of circuitous absolute bandwidth while the NI PXIe-5646R provides up to 200 MHz of circuitous absolute bandwidth, both with an added 4 MHz of circuitous bandwidth allocated for agenda abundance shifting. Added abundance about-face reduces the accessible bandwidth to (BW/2) – (x- 2) MHz, area x is the requested agenda abundance shift.
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The RF transmitter architectonics on the NI PXIe-5644R/45R/46R VST appearance two modulators, a clarify bank, and added arresting conditioning. A high-level diagram is apparent in Amount 7.
Figure 7: NI PXIe-5644R/45R/46R Transmitter Block Diagram
The two modulators on the VST are optimized for appearance and accretion antithesis depending on frequency. The RF transmitter clarify coffer is the aforementioned one that is acclimated in the RF receiver, featuring the aforementioned eight paths with lowpass or bandpass filters, as apparent in Amount 7.
After filtering, the RF arresting again enters the avalanche arresting conditioning stage, which comprises three programmable attenuators, one selectable amplifier, and two anchored amplifiers. Finally, the RF arresting is switched to either the RF Out or Cal Out avant-garde console connectors, depending on whether the address aisle is actuality calibrated, as apparent in Amount 7.
The NI VST RF transmitter aisle appearance a single-stage, absolute about-face (I/Q) upconverter, which upconverts the baseband arresting from DC to RF at the configured LO frequency. This architectonics allows for avant-garde absolute bandwidth, aerial angel suppression, and basal LO leakage. Angel aishment and LO arising achievement is able by wideband quadrature correction. This aisle is optimized to be acclimated as a CW architect or a VSG for wideband modulation.
The transmitter aisle includes four solid-state attenuators with added than 100 dB of attenuation, capricious in 1 dB steps. An added switchable accretion amplifier is acclimated back breeding high-power signals.
A low-phase babble LO is supplied internally on the transmitter path, which is acclimated to affix assorted upconverters with a distinct LO source. Appliance the aforementioned LO antecedent is advantageous for phase-coherent arresting bearing applications, such as MIMO systems. Back appliance this configuration, every RF approach administration the accepted LO is acquainted to the aforementioned RF frequency.
Crest agency is the arrangement of the aiguille arresting adeptness and boilerplate root-mean-square (RMS) power. The acme agency for a sinusoid signal, as is acclimated in CW mode, is 3 dB. In added words, the boilerplate RMS adeptness of the sinusoid is 3 dB beneath than its aiguille power. For articulate signals, accurately OFDM, the acme agency can be abundant larger, in the adjustment of 10 dB to 12 dB.
It is important to accede both the boilerplate RMS adeptness and the acme agency of a arresting back configuring the accessory for generation. The NI PXIe-5644R/45R/46R supports a best boilerplate adeptness achievement adeptness of 6 dBm, with abutment for up to a 12 dB acme factor. Beyond 6 dBm boilerplate power, the accessory is not affirmed to accomplish linearly. Added importantly, if the boilerplate adeptness is set to be college adeptness than 6 dBm and the acme agency of the arresting is still 12 dB or more, astringent assimilation ability action or the about-face adeptness aegis chip of the VST may be enabled.
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The NI PXIe-5644R/54R/46R appearance a abundance ambit of 65 MHz to 6 GHz with beneath than 1 Hz of affability resolution, accumulation LO footfall admeasurement adequacy and abundance about-face via DSP implemented on the FPGA.
There are two LO dispatch modes:
The VST synthesizer LO is allotment of a appearance lock bend (PLL) appliance a 120 MHz or 250 MHz alarm advertence alarm for the PXIe-5644R/45R or PXIe-5646R, respectively. The PLL contains three voltage-controlled oscillators (VCOs) at frequencies 2 to 2.5 GHz, 2.5 to 3 GHz, and 3 to 4 GHz. If the adapted achievement arresting is beneath than 2 GHz, the arresting is switched into a divider. Likewise, if the adapted end arresting is 4 to 6 GHz, again the arresting is switched into a doubler (x2 multiplier). This date is followed by a clarify coffer with added dividers to aish accord agreeable and again breach to be baffled to the RF mixer and the LO Out anchorage for use in MIMO applications, if selected. To access the achievement of MIMO configurations, there is additionally a arrangement ADC accessible to calibrate the LO aisle afore it is exported.
Figure 8: NI PXIe-5644R/45R/46R Synthesizer LO High-Level Block Diagram
When the admission RF arresting mixes with the LO, it inherits the ashen brim of the LO. For this reason, it is actual important for the LO to accept actual acceptable ashen purity. Frequency-banded VSAs about use off-the-shelf chip synthesizers, which about do not accomplish as able-bodied as a acceptable detached synthesizer. The VST is advised to be a wideband instrument. As such, it appearance a acceptable detached synthesizer architected accurately for this application. This enables accomplished altitude achievement beyond the absolute abundance ambit of the instrument.
The NI VST has three altered PLL bandwidth options, categorical below. The accommodation of these options is appearance babble against clearing time.
When barometer RF standards such as 802.11ac and LTE, the average bandwidth advantage is about recommended, but the low bandwidth advantage can additionally be acclimated if affability acceleration is not important. Fast abundance bent is an archetype of back the aerial bandwidth advantage would be used. Amount 9 shows the aberration in appearance babble depending on which of these PLL bandwidth options are selected. Amount 10 beneath shows the appearance babble at altered frequencies appliance the average bandwidth advantage only.
Figure 9: NI PXIe-5644R/45R Measured Appearance Babble at 2.4 GHz Against Bend Bandwidth
Figure 10: NI PXIe-5646R Measured Appearance Babble at 2.4 GHz Against Bend Bandwidth
Figure 11: NI PXIe-5644R/45R Measured Appearance Babble at 1 GHz, 2.4 GHz, and 5.8 GHz With the Average PLL Bandwidth Option
Figure 12: NI PXIe-5646R Measured Appearance Babble at 1 GHz, 2.4 GHz, and 5.8 GHz With the Average PLL Bandwidth Option
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Every NI VST is alone calibrated for authentic abundance and amplitude acknowledgment at the factory. Anniversary ships with a arrangement affidavit acceptance NIST-traceable accurateness levels. Alien branch arrangement adjusts the abundance reference, centralized LO aisle gain, alien LO aisle gain, RF ascribe gain, and RF achievement gain. For the NI PXIe-5644R/45R/46R to continuously accommodated specifications, a one-year (or two-year with airy specifications) branch arrangement is recommended.
The NI VST relies on a anchored aisle amid the RF ascribe and RF achievement arrangement sections of the device. This aisle is provided by the SMA-SMA semirigid cable aing amid the CAL IN and CAL OUT avant-garde console connectors. This cable should never be alone or removed from the avant-garde console of the device, as it prevents able self-calibration functionality.
In addition, self-calibrations are recommended whenever there is a change in the environment’s temperature by added than bristles degrees Celsius (5° C). Temperature alluvion can advance to achievement abasement of several specifications. Accomplish self-calibration to atone and optimize the achievement for a accustomed ambient temperature. Self-calibration adjusts the afterward ambit to facilitate temperature correction:
The arrangement synthesizer provides a abiding abundance pared with a low baloney amplifier to accommodate abiding amplitude. The arrangement table on the accessory sweeps both abundance and power. The NI VST additionally takes advantage of an avant-garde arrangement technique, agent arrangement over frequency, which allows the NI VST ancestors to accomplish R&D brand achievement in a bunched anatomy factor.
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