Analysis of Baseband Extending the N9020A MXA I Q … · Analysis of Baseband IQ Signals Page 1 MTT...

Analysis of Baseband IQ Signals

MTT 2008

Analysis of Baseband

I Q Signals

Extending the N9020A MXA

to Baseband and RF

Roger Jungerman

R&D Hardware Designer

Signal Analysis Division


MTT 2008

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Wireless System Design

Baseband and RF signals.

How do we test it?


MTT 2008


IQ Modulation

I and Q inputs are typically provided by digital baseband generation and dual-digital to analog conversion


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IQ Modulation

IQ modulation makes it possible to transmit complex information content. If properly calibrated.


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Digital Baseband

Digital baseband input and RF output only

Digital Signal

Processing

DAC DAC

Digital Input

IntegratedASIC


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Measurement of Digital IQ Signals

Digital Logic Analyzer with 89601A VSA software for IQ analysis

Dig RF V3


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Measurement of Baseband across Domains

DSP

Multiple Signal InterfacesCommon Signal

Analysis Platform

Digital (SSI) IF/RF BB (I-Q)

Logic Analyzer Signal Analyzer

DUT

• common measurements

• common interface

• single learning curve

MXA BBIQ or scope


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Measurement of Analog IQ Signals

Oscilloscope for baseband has some limitations

RF Analog Baseband

MXA Spectrum Analyzer MXA BBIQ

89601A VSASoftware in both

domains


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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


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Interface Board

Front Panel Board

Main BoardOverlays

Coax Ribbon Cable

Revised Front Frame

Adding Baseband to MXA


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MXA with Baseband Inputs and Calibrator

MXA BBIQ measures both baseband and RF signals


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LO

FFT

14-bit ADC, 90

MS/sRF input path

2 dB step

ATT

Gain/preamp

LO phase optimization

Swept or FFT

160 narrow step

RBW

Digital detector suite

16-bit ADC, 100 MS/sAnalog BB inputs

Switched Gain

amplifier

1 M Ω /

50 ΩZ Select

Real-time IQ

corrections

Re-sampling/

Decimation

500 MSaCapture Memory

Single

ended/

Differential

Select

Probe

Interface

CalBaseband Calibrator Out

• Up to 26.5 GHz

• 10 or 25 MHz BW

• 4 MSa memory

• Baseband to 40 MHz (for 1ch/2ch)

• 10, 25 or 40 MHz BW

• 500 MSamemory

MXA Baseband and RF


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MXG can be used for baseband generation with

baseband outputs


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The Need for Accurate Calibration

A simple Optimized Single-sideband Modulation (-624 kHz offset)

)624.02cos( tMHzI ∗∗= π )624.02sin( tMHzQ ∗∗−= π


MTT 2008


The Need for Accurate CalibrationGain mismatch causes images

)624.02cos(*059.1 tMHzI ∗∗= π )624.02sin( tMHzQ ∗∗−= π

0.5 dB Gain Mismatch


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The Need for Accurate CalibrationOffset causes “LO feedthrough”

Offset of 3%

03.0)624.02cos(*059.1 +∗∗= tMHzI π )624.02sin( tMHzQ ∗∗−= π


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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


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Internal CalibratorGuided calibration

Easy to understand user interface for calibration


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A Test Device for Baseband and RF

I Q Modulator Evaluation Board: TRF3702


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MXA Calibrates the Baseband Inputs

Measured images are due to IQ Modulator DUT


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Add Impairments to Optimize Performance

Add phase skew of 2 degrees to MXG output to reduce image


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Probing Makes it Possible to Measure on the DUT

Test board with two passive probes for a differential signal


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Types of Probes for MXA

Both active and passive probes are supported with the InfiniiMax interface

113xA Active Differential Probe• Single Connection Differential Measurements

• Probe ID

• 50 Ohm MXA input• Lowest capacitance

• No compensation required

• Probe calibration supported

1161A 10:1 Passive Probe• Low Cost

• Probe ID

• 1M Ohm MXA input• Good sensitivity

• Probe compensation and calibration supported


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Passive Probe Compensation

Balances the AC and DC gains of 10 MOhm passive probes


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Probe Calibration

Balances I Q attenuation and frequency responseFor active and passive probes


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Demodulation Applications

Mobile WiMAX baseband and RF support


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LTE baseband and RF support


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Flexible 89601A VSA demodulation of an OFDM signal


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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

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