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© 2004 Altera Corporation
Wideband Modem Design Using FPGAs
Wideband Modem Design Using FPGAs
Rob PeltAltera
Rob PeltAltera
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
2© 2004 Altera Corporation - Confidential
OutlineOutlineAnalog Up ConversionDigital Up Conversion (DUC)Polyphase Digital Up ConversionConclusionQuestions
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
3© 2004 Altera Corporation - Confidential
Analog Up ConversionAnalog Up ConversionCurrent Modems− Digital Baseband− Digital Intermediate Frequency (IF) Possibly− Analog RF (Possible Direct Up Conversion)
PowerAmplifier
Filter
VCO
NCO
LowNoise
AmplifierFilter
VCO
NCO
Switch
FPGA-based Digital IF & Baseband Processing
Digital-to-
Analog
Analog-to-
Digital
InterfaceBasebandProcessing
Antenna
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
4© 2004 Altera Corporation - Confidential
Analog Digital Up ConversionAnalog Digital Up ConversionImpairments are Introduced− High Order Mixing Products
3rd, 5th, 7th, . . . Order Terms− Error Vector Magnitude (EVM) Impairments
I/Q Phase & Magnitude Imbalance− Carrier Feed-through− Harmonics− Sideband Noise
Analog Filter Characteristics− Non-Linear Phase− Group Delay Variation
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
5© 2004 Altera Corporation - Confidential
Moving from Analog to DigitalMoving from Analog to DigitalAdvantages− Higher Performance− Lower Implementation Loss− Time to Market− Flexibility
Disadvantages− Incremental Cost− Higher Power
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
6© 2004 Altera Corporation - Confidential
Digital Up ConversionDigital Up Conversion
Quadrature Digital IFEliminates I/Q Imbalance (EVM Distortion)Single D/A Converter
ModulatorDigital-to-
Analog
VCO
PowerAmplifierNCO
CICFIR
CICFIR
FPGA
Anti-Aliasing
Filter
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
7© 2004 Altera Corporation - Confidential
Digital Up Conversion in FPGADigital Up Conversion in FPGACurrent FPGAs are Feature Rich− Arithmetic Operators− Embedded Memory− High-Speed I/O− PLL
FPGA Clock Speeds are >300 MHz− Bandwidths up to 150 MHz
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
8© 2004 Altera Corporation - Confidential
Altera’s Stratix II FPGA FamilyAltera’s Stratix II FPGA Family
123849,383,040179,400EP2S180
121924,520,44890,960EP2S90
6,747,840
2,544,192
1,369,728
419,328
Total Memory
Bits
252
144
64
48
18x18Multipliers
EP2S130
EP2S60
EP2S30
EP2S15
Device
12132,540
1260,440
633,880
615,600
PLLEquivalent Logic
Elements
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
9© 2004 Altera Corporation - Confidential
Digital Up ConverterDigital Up Converter
314 MHzFFT (256 point)
404 MHzNCO
339 MHzFIR Filter
Maximum SpeedComponent
Stratix II Common Building BlocksSpeeds at >300 MHzNyquist Bandwidth of ~150 MHz
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
10© 2004 Altera Corporation - Confidential
Polyphase ApproachPolyphase ApproachCurrent D/A converters Have Sample Rates of >1 GSPS− Bandwidth of >500 MHz
Standard DUC Approaches Limit Bandwidth to ~150 MHZPolyphase DUC can Take Advantage of D/A Sample Rates− Bandwidths up to DAC Nyquist
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
11© 2004 Altera Corporation - Confidential
Polyphase ApproachPolyphase ApproachFamiliar Polyphase DecompositionEach Sub-Filter Processes a Different Phase of the Input SignalOutput Commutator Supplies Up-Sampling
Polyphase Sub-Filter
Polyphase Sub-Filter
Polyphase Sub-Filter
x(t)
y(t)
Commutator
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
12© 2004 Altera Corporation - Confidential
Polyphase Digital Up ConversionPolyphase Digital Up ConversionPolyphase Decomposition of Up-ConversionSub-DUC Replaces Sub-FiltersLow Voltage Differential Signaling (LVDS)− Serializer Mux− Replaces Commutator
Digital-to-Analog
Converter
NCO
Sub-Filter
LVDSSerializer
LVD
S
Sub-DUC 0
Sub-DUC 1
FPGA-based Polyphase Modem
Sub-DUC N
BasebandProcessing
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
13© 2004 Altera Corporation - Confidential
Sub-DUC ConstructionSub-DUC ConstructionMixerFilter− Normal Polyphase Decomposition
NCO− Frequency− Initial Phase− Spectral Inversion Compensation
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
14© 2004 Altera Corporation - Confidential
NCO FrequencyNCO FrequencySet frequency Based on Desired Alias
( )gen s_nco
__ gen s_nco
for F < F /2 * for F > F /2
gena gen
gen s nco
FF
F F alias = −
Where:Fa_gen is alias frequency setting for the NCOFgen is the desired output frequencyalias is the Nyquist zone number
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
15© 2004 Altera Corporation - Confidential
NCO PhaseNCO PhasePhase Set for Alias Frequency
Where:N is the number of sub-DUCsFs_dac is the clock speed of the DACFgen is the desired output frequency
_
360* genN
s dac
FF N
φ =∗
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
16© 2004 Altera Corporation - Confidential
ConclusionConclusionFPGAs are Well Equipped for Digital Up ConversionD/A Converters with GHz Sampling Rates are AvailableUsing Polyphase Decomposition & Aliasing, FPGAs Can Be Used to Interface to the GHz D/A Converters
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
© 2004 Altera Corporation
Thank YouThank YouFor More Information Visit www.altera.comFor More Information Visit www.altera.com
Proceeding of the SDR 04 Technical Conference and Product Exposition. Copyright © 2004 SDR Forum. All Rights Reserved
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