Analysis of Baseband
I Q Signals
Extending the N9020A MXA
to Baseband and RF
Roger Jungerman
R&D Hardware Designer
Signal Analysis Division
Analysis of Baseband IQ Signals
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MTT 2008
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Wireless System Design
Baseband and RF signals.
How do we test it?
Analysis of Baseband IQ Signals
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IQ Modulation
I and Q inputs are typically provided by digital baseband
generation and dual-digital to analog conversion
Analysis of Baseband IQ Signals
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IQ Modulation
IQ modulation makes it possible to transmit complex
information content. If properly calibrated.
Analysis of Baseband IQ Signals
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Digital Baseband
DAC
DAC
Digital Signal
Processing
Integrated
ASIC
Digital Input
Digital baseband input and RF output only
Analysis of Baseband IQ Signals
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Measurement of Digital IQ Signals
Dig RF V3
Digital Logic Analyzer with 89601A VSA software for IQ analysis
Analysis of Baseband IQ Signals
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Measurement of Baseband across Domains
DUT
DSP
Digital (SSI)
Logic Analyzer
BB (I-Q)
IF/RF
MXA BBIQ or scope Signal Analyzer
Multiple Signal Interfaces
• common measurements
• common interface
• single learning curve
Common Signal
Analysis Platform
Analysis of Baseband IQ Signals
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Measurement of Analog IQ Signals
89601A VSA
Software in both
domains
RF
MXA Spectrum Analyzer
Analog Baseband
MXA BBIQ
Oscilloscope for baseband has some limitations
Analysis of Baseband IQ Signals
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Analog Baseband Measurement Requirements
• Signal to Noise Ratio (Oscilloscope ADC is 8 or fewer effective bits)
• Single-ended and Differential measurements (Oscilloscope SE only)
• Accurate complex frequency response calibration (EVM)
• Low distortion
• Very accurate I Q channel-match calibration (Images)
• Extremely low offset voltage (LO feedthrough)
• Active and passive probe support
• Integrated solution with RF Spectrum analyzer measurements
MXA BBIQ solves baseband issues
Analysis of Baseband IQ Signals
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Adding Baseband to MXA
Revised Front Frame
Overlays
Main Board
Interface Board
Front Panel Board
Coax Ribbon Cable
Analysis of Baseband IQ Signals
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MXA with Baseband Inputs and Calibrator
MXA BBIQ measures both baseband and RF signals
Analysis of Baseband IQ Signals
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MXA Baseband and RF
14-bit ADC, 90
MS/s
FFT
RF input path
• Up to 26.5 GHz
• 10 or 25 MHz BW
• 4 MSa memory
2 dB step
ATT
Gain/preamp
LO
Swept or FFT
LO phase
optimization
Analog BB inputs
Digital detector suite
160 narrow step
RBW
16-bit ADC, 100 MS/s
• Baseband to 40
MHz (for 1ch/2ch)
Probe
Interface
1MΩ/
50 Ω
Z Select
Single
ended/
Differential
• 10, 25 or 40 MHz
BW
Switched
Gain
amplifier
• 500 MSa
memory
Select
Cal
Baseband
Calibrator Out
Real-time IQ Re-sampling/
corrections
Decimation
500 MSa
Capture Memory
Analysis of Baseband IQ Signals
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MXG can be used for baseband generation with
baseband outputs
Analysis of Baseband IQ Signals
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The Need for Accurate Calibration
A simple Optimized Single-sideband Modulation (-624 kHz offset)
I = cos( 2π ∗ 0.624 MHz ∗ t )
Q = − sin(2π ∗ 0.624MHz ∗ t )
Analysis of Baseband IQ Signals
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The Need for Accurate Calibration
Gain mismatch causes images
I = 1.059 * cos( 2π ∗ 0.624 MHz ∗ t )
0.5 dB Gain Mismatch
Q = − sin( 2π ∗ 0.624MHz ∗ t )
Analysis of Baseband IQ Signals
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The Need for Accurate Calibration
Offset causes “LO feedthrough”
I = 1.059 * cos( 2π ∗ 0.624 MHz ∗ t ) + 0.03
Offset of 3%
Q = − sin( 2π ∗ 0.624 MHz ∗ t )
Analysis of Baseband IQ Signals
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Internal Calibrator
Accurately calibrates gain mismatch vs. frequency and DC offset
Time domain edge used to calibrate all frequencies
Much more accurate than a typical oscilloscope calibration
Analysis of Baseband IQ Signals
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Internal Calibrator
Guided calibration
Easy to understand user interface for calibration
Analysis of Baseband IQ Signals
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A Test Device for Baseband and RF
I Q Modulator Evaluation Board: TRF3702
Analysis of Baseband IQ Signals
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MXA Calibrates the Baseband Inputs
Measured images are due to IQ Modulator DUT
Analysis of Baseband IQ Signals
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Add Impairments to Optimize Performance
Add phase skew of 2 degrees to MXG output to reduce image
Analysis of Baseband IQ Signals
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Probing Makes it Possible to Measure on the DUT
Test board with two passive probes for a differential signal
Analysis of Baseband IQ Signals
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Types of Probes for MXA
113xA Active Differential Probe
1161A 10:1 Passive Probe
• Single Connection Differential Measurements
• Probe ID
• 50 Ohm MXA input
• Lowest capacitance
• No compensation required
• Probe calibration supported
• Low Cost
• Probe ID
• 1M Ohm MXA input
• Good sensitivity
• Probe compensation and calibration supported
Both active and passive probes are supported with the InfiniiMax interface
Analysis of Baseband IQ Signals
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Passive Probe Compensation
Balances the AC and DC gains of 10 MOhm passive probes
Analysis of Baseband IQ Signals
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Probe Calibration
Balances I Q attenuation and frequency response
For active and passive probes
Analysis of Baseband IQ Signals
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Demodulation Applications
Mobile WiMAX baseband and RF support
Analysis of Baseband IQ Signals
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Demodulation Applications
LTE baseband and RF support
Analysis of Baseband IQ Signals
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Demodulation Applications
Flexible 89601A VSA demodulation of an OFDM signal
Analysis of Baseband IQ Signals
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Conclusions
• MXA BBIQ enables analog baseband and RF measurements
in the same instrument
• Offset and gain calibrations for accurate modulation
measurements
• Active and passive probe support makes it possible to access
signals on the test device
• Demodulation applications work in both the baseband and RF
domains
Analysis of Baseband IQ Signals
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MTT 2008