Agilent Technologies Webcam 89600 User Manual

Agilent

Acqiris Broadband High-Speed Digitizers

Using 89600 Vector Signal Analyzer Software

Application Note

Vector signal analysis using

Agilent Acqiris broadband digitizers.

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This product note describes the characteristics, setup, and operation of a broadband

vector signal analyzer (VSA) comprised of an Agilent Acqiris U1066A (DC440, DC438)

or U1065A (DC282, DC252, DC222) high-speed digitizer and the 89600 vector signal

analyzer software. By taking advantage of the layered architecture and extensive digital

signal processing (DSP) routines of the 89600 VSA software, the digitizer becomes

a new “front end” data acquisition subsystem for the VSA. This hardware-software

combination provides up to 2 GHz of analysis bandwidth depending on the digitizer

used. See Table 1 for the supported digitizer models and the corresponding analysis

bandwidths. Appendix A contains suggestions for ultra-wideband downconverters.

1 Overview

The 10- and 12-bit, high sample rate analog-to-digital converter (ADC) in the Acqiris

digitizers produces the large analysis bandwidths shown in Table 1. These bandwidths

are capable of providing a spurious-free dynamic range greater than or equal to 40 dB

for the U1065A and greater than or equal to 75 dB for the U1066A. This is sufﬁcient for

1.5 to 2% error vector magnitude measurements in most cases. For spectrum measure-

ments with higher dynamic range, a traditional spectrum analyzer should be used.

Table 1. Agilent Acqiris digitizers supported by 89600 VSA software

Model

No of

channels

Max

sample rate

Frequency

range

Default

memory

Optional

memory

U1066A-001 (DC440)

U1066A-001 (DC440) HF input

U1066A-002 (DC438)

U1065A-001 (DC222)

U1065A-002 (DC252)

U1065A-004 (DC282)

1. Max span = 164 MHz

400 M

420 M

200 M

8 G

4 G

8 G

4 G

dc – 100 MHz

1 MHz – 300 MHz

dc – 78.125 MHz

dc – 2 GHz

dc – 1.5625 GHz

dc – 2 GHz

4 M

1 M

512 k

1 M

512 k

8 M

128 M, 1 G

64 M, 512 M

128 M, 1 G

64 M, 512 M

dc – 1.5625 GHz

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1.189600 VSA software

The 89600 vector signal analyzer software is the heart of the broadband VSA. This software

provides ﬂexible tools for analyzing and demodulating even the most advanced digital modu-

lations, including those not deﬁned by an established standard.

The VSA makes measurements on signals in the time and frequency domains using either

the BB (baseband) or IF Zoom mode. In BB mode, the analysis frequency range is from 0 Hz

to the stop frequency. In IF Zoom mode, the analysis frequency range is deﬁned by center

frequency and span. There is also an I+jQ mode for analyzing two baseband quadrature

channels. Results for any mode can be displayed as magnitude

or phase, in I/Q and several other formats.

With the optional digital demodulator, Option 89600-AYA, modulation quality measurements

in the form of error vector magnitude (EVM) can be made on digital wireless communica-

tions signals with bandwidths of hundreds of MHz. In addition, powerful diagnosis capabili-

ties allow you to determine the exact impairments that cause a digitally modulated signal to

fail quality standards.

The features of the digital demodulator include variable-block-size signal acquisition, pulse

burst edge search, synch word search and a user-controllable adaptive equalizer.

User-selectable ﬁlter types include cosine (raised and square-root raised), Gaussian, low-

pass, and user-deﬁned. You can vary the ﬁlter alpha/BT shape factor. Supported modulation

formats for both burst and continuous carriers include FSK, BPSK, QPSK, OQPSK, DQPSK,

π/4DQPSK, 8PSK, QAM (16 to 1024), and MSK.

In addition, the 89600 software provides a signal record feature for later playback and

analysis.

1.2 Required software revisions

Using the 89600 Series VSA software with Agilent Acqiris high-speed digitizers requires

compatible software versions:

Table 2. Required software versions

Agilent Acqiris Software for

Windows®

AcqirisSoftware 3.2

(Driver AqDrv4.dll 4.13) or later

For baseband operation:

89600 VSA

v8.00 or later

1.0 or later

Acqiris VSA Server

For HF operation:

89600 VSA

v9.00 or later

2.0 or later

Acqiris VSA Server

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The 89600 VSA software must be installed on a computer.

2 Install 89600 VSA

Software

Installation for standard operation

Insert the Agilent Technologies 89600 Series Software CD-ROM in your standard PC

and follow the instructions in the installation wizard. When the Installation Manager

window opens, click Install 89600 Series Software. In the Hardware Support window,

select Acqiris VSA Server. This will avoid installing unnecessary components on your

computer. After the software and hardware support is installed, exit the Installation

Manager window.

Installation for embedded operation

Operation of the 89600 Series software on an embedded Compact PCI computer is

similar to operation on a standard PC. The instructions for standard operation can be

followed here as well using a LAN or USB accessible CD drive.

Note: Before you can run the VSA with an Agilent Acqiris digitizer, make sure

the Agilent Acqiris digitizer hardware and driver software are installed and

configured as directed in the 89600 Series Installation and VXI Service Guide

found on your Agilent Technologies 89600 Series Software CD or go to

www.agilent.com/find/89600 then click on Technical Support > Manuals.

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Connect the digitizer to the computer as shown in Figure 1a or 1b. There are two options

for the connection, by remote computer or by embedded computer.

3 Hardware

Conﬁguration

3.1 I/O between computer and digitizer

Operation of the 89600 Series software on an embedded Compact PCI computer

is similar to operation on a standard PC. The instructions for standard operation

can be followed here as well using a LAN or USB accessible CD drive.

Agilent Acqiris data acquisition system

Agilent Acqiris digitizer

Optional anti-alias LPFs

Interface

Input Ch 1 Input Ch 2

(Digitizer Ch 1) (Digitizer Ch 2)

Figure 1a. Digitizers connected through CompactPCI to PCI interface

The digitizers can be connected through various interface types from a

CompactPCI crate to either a desktop PC or a portable PC.

Agilent Acqiris data acquisition system

Agilent Acqiris digitizer

Optional anti-alias LPFs

Embedded computer

Input Ch 1 Input Ch 2

(Digitizer Ch 1) (Digitizer Ch 2)

Figure 1b. Digitizers connected through embedded single board PC

Alternatively, the digitizers can be controlled by an embedded computer as

shown in Figure 1b.

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3.2 Anti-alias ﬁlters and alias exposure-free mode

The broadband VSA can be conﬁgured to be essentially alias-free by using the full

rate sampling mode and installing an external lowpass ﬁlter on the digitizer input.

Use BNC-f to SMA-m and SMA-f to BNC-m adapters to connect the ﬁlter’s SMA

connectors to the digitizer in case the digitizer has BNC connectors.

Table 3. External lowpass ﬁlters

Digitizer model

Cutoff frequency Filter part number

U1066A-002 (DC438)

U1066A-001 (DC440)

U1065A (DC252 (2 ch),

DC282 (2 ch))

U1065A (DC222, DC252 2000 MHz

(1 ch), DC282 (1ch))

90 MHz

100 MHz

1650 MHz

Mini-circuits BLP/SLP-90

Mini-circuits BLP/SLP-100

Mini-circuits SLP-1650

Mini-circuits SLP-2000

1. Mini-Circuits, Inc., 1-800-854-7949, www.minicircuits.com.

2. For the HF input a 300 MHz lowpass ﬁlter will avoid aliasing from signals above 300 MHz, but in-band

and out-of-band aliasing is still possible since full rate mode is not supported with the HF input.

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4.1 Basic operation

4 Operation

Operation of the broadband VSA is substantially the same as that of the 89600

VSA. See the following sections for some differences or special conﬁgurations.

There is an online Tutorial and Getting Started Guide under the Help/Roadmap

toolbar in the 89600 software.

4.2 Sampling modes: full rate and user rate

Full rate mode

When the Sample Mode is set to full rate using the Utilities/Hardware/ADC1

/Agilent Acqiris One Channel Digitizer/Conﬁgure/Sample Mode/Edit menu

path for the U1065A-001 or Utilities/Hardware/ADC1 /Agilent Acqiris Two

Channel Digitizer/Conﬁgure/Sample Mode/Edit menu path for all the other

models, the digitizer sample rate is ﬁxed at the maximum for each digitizer

model according to Table 4.

Table 4. Sample rates of Acqiris digitizers in full rate mode

Digitizer model

No. of channels

Full sample rate

U1066A-001 (DC440)

U1066A-002 (DC438)

U1065A-001 (DC222)

U1065A-002 (DC252)

U1065A-004 (DC282)

400 M

200 M

8 G

4 G

8 G

4 G

With the addition of the anti-alias lowpass ﬁlter described above, this mode is

free of alias exposure zones. This means that no signal anywhere in the range

of the VSA’s center frequency will alias upon the desired signal and corrupt the

measurement.

There is a trade-off when using this mode. Although the digitizers have deep

memories allowing long record lengths, if a longer Main Time (or Result Length

for digital demodulation) is needed for more resolution in the frequency domain

a different sample mode may be required. Go to the Conﬁgure menu, click on

Sample Mode/Edit and select User Rate from the drop-down menu. The Main

Time limit for any sample rate is shown in the operating region curves that

appear in Appendix C.

NOTE: Any limitation to Main Time (or Result Length) will be indicated by the

inability of the software to increase the Main Time or decrease RBW when

Number of Frequency Points is increased.

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User rate mode

The user rate setting allows you to directly control the digitizer’s sample rate. In

this mode you select the digitizer sample rate to be used. The actual sample rate

selected will be the highest rate that is less than or equal to the “user sample

rate” setting. By controlling the digitizer’s sample rate you can directly inﬂuence

the update rate of the VSA. This is because sample rate directly affects the num-

ber of points the digitizer must transfer to the PC. Certain measurements can be

made signiﬁcantly faster by limiting the digitizer sample rate due to reduced data

transfer requirements.

There are two types of signal aliasing to be concerned with when using the

89600 VSA application with an Agilent Acqiris digitizer. The ﬁrst is aliasing of

unwanted out-of-band signals into the measurement span. This will not be a

problem with the majority of clean, single-signal devices. However, devices with

multiple or spurious signals could have this type of aliasing. Section 6 describes

how to perform a check to determine if there are any unwanted signals present

that can alias down into the measurement span. A second type of aliasing hap-

pens when the sample rate causes the in-band signal to fold over on itself. This

in-band (or self-) aliasing is avoided in full rate mode by automatically selecting

the highest sample rate. However, in user rate mode in-band aliasing may be a

problem. To avoid in-band aliasing you must select a suitable sample rate based

on your measurement center frequency and span.

To avoid in-band aliasing the digitizer sample rate (F ) must be selected so that

the analysis span falls within conﬁned regions. Staying within these regions

prevents the analysis span from being positioned too close to F /2. When F

is selected so that the span is conﬁned to be within a single gray box (see

diagrams below), in-band aliasing is avoided. See the following table for the

equations that describe these in-band alias-free regions.

The primary use of user rate mode is to increase maximum waveform length that

can be acquired or to increase the update rate. In all cases, user rate measure-

ments must be been carefully engineered to avoid unwanted alias signals.

Baseband:

F /2

F /2.56

Zoom:

(n + 1)F

n * F

(n + 1/2) * F

Figure 2. Avoiding in-band aliasing by selecting FS within a conﬁned span

NOTE: User Rate is the only available mode in HF operation. The VSA does not

attempt to avoid alias exposure regions when in User Rate mode.

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This table summarizes the difference in approach to alias protection between

the various sample modes:

Table 5. Varying approaches for alias protection

Full rate Both in-band and out-of-band aliasing are prevented through use

of the maximum sample rate and an appropriate lowpass ﬁlter.

User rate You are responsible to avoid in-band aliasing through appropriate

selection of sample rate based on center frequency and span. To

ensure no in-band aliasing is present the digitizer sample rate (FS)

must be selected to meet this criteria:

Baseband: F

≤ F /2.56

STOP

Zoom: (n*F )/2 ≤ F

- (1.28 * F

)/2

SPAN

CENTER

AND

((n+1)*F )/2 ≥ F

+ (1.28 * F

)/2

SPAN

CENTER

where n = 1,2,3,4…

Out-of-band aliasing is minimized through use of appropriate

low-pass ﬁlter. Use of Alias Checker macro (Section 6) is required

to detect other unwanted out-of-band signal aliasing.

(Note: aliasing of unwanted signals can be eliminated through use

of appropriate bandpass filter.)

Another concern in user rate mode is that you may see unwanted amplitude

variability in two channel measurements. This can occur if any part of the mea-

surement frequency span falls within the regions deﬁned by:

(2*n+1) x F /2 0.1 x F

where n = 1, 2, 3, 4 …

where F is the actual digitizer sample rate. Make sure you choose a sample rate

where such overlap does not occur.

4.3 Differences from 89600 VSA operation

•

No Magnitude Trigger (however, Channel Trigger is available).

Possible limitation of movement on the operating region curve to avoid alias

corruption of the measured signal. This depends on the settings of Center

Frequency, Span, Sample Mode, and Number of Frequency Points. There is

also potential interference due to the alias products of out-of-band signals.

(See Section 6.)

•

No built-in wideband calibrator. The frequency response corrections are

determined from factory data.

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The operating region curves for the broadband VSAs are different from those of

standard VSAs because the Main Time Length may be limited for some sample

rate, center frequency, and span combinations. The differences are due to three

hardware characteristics of the ultra-wideband ADCs in the Agilent Acqiris

digitizers:

5 Time and

Frequency Span

Operating Region

•

A much higher sampling rate

The lack of a hardware decimator, which means the decimation must be

performed by the software from same-length records taken at much higher

sampling rates

•

Limited memory capacity

5.1 The relationship of main time length, span, and

sample rate

The record length or Main Time Length of a measurement is shown in the lower

right corner of a spectrum or time display window. This is the length of time the

digitizer sampled the input waveform for the measurement. These samples are

transferred to the DSP and measurement algorithms running on the software.

Maximum Main Time Length is normally adjusted by setting Number of Frequency

Points in the MeasSetup/ResBW menu ResBW Coupling is set to Auto, and

ResBW mode is set to Arbitrary or 1-3-10. The Time tab can then be used to set

Main Time Length up to this maximum limit. This setup keeps Main Time Length

maximized and within the DSP requirements.

Although Main Time Length can be adjusted directly by the MeasSetup/Time

menu, it cannot be greater than the limit imposed by the Number of Frequency

Points line on the operating region chart. See the online Help tool for a complete

discussion.

Note: The maximum Main Time Length can be found as follows:

The relationship between the parameters is shown below:

Max Main Time Length = Number of frequency points

Span

where Span = Sample rate

1.28

Max Main Time Length = 1.28 x Number frequency points

Sample rate

where sample rate = current sample rate computed by the software for alias-

free measurements

Maximum Main Time Length may be further limited by digitizer memory depth.

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5.2 Operating region curves for Agilent Acqiris digitizers

Several interrelated characteristics of both the Acqiris digitizers and the 89600 VSA

software combine to form a region within which the VSA is constrained to operate.

The 89600 VSA software characteristics that affect this operating region include

maximum number of time points, the minimum number of time points (not user

settable), a maximum acquisition record size (not user settable) and a maximum

decimation factor (not user settable). The Digitizer characteristics that affect the

operating region are sample rate and memory depth. This section describes the

effects each of these parameters has on the VSA operating region.

The operating region is described in terms of span and time record length. For a

given window type it could just as easily be described in terms of span and RBW.

Figure 3 shows the effects of the number of time points the 89600 VSA software is

allowed to collect. Because sample spacing is inversely proportional to span, the

record length decreases as span increases. Although a family of lines is shown,

only two deﬁne the operating region at any one time. The lowest line gives the

smallest time record length allowed for any given span. The position of this line

is determined by minimum number of time points (16) the VSA requires in a time

record. The line that deﬁnes the upper time record length boundary is positioned

by the maximum number of time points the VSA allows in a time record . The maxi-

mum number of time points is determined by the Frequency Points setting (Meas-

Setup/ResBWFrequency Points). The 89600 VSA is constrained to operate in the

region between these two lines. Note that the operating lines of Figure 3 are the

same for all digitizer models.

Operating region: number of frequency points limits

1.E+01

1.E+00

1.E-01

1.E-02

1.E-03

409601

204801

102401

1.E-04

51201

25601

12801

6401

3201

1601

801

1.E-05

1.E-06

1.E-07

1.E-08

401

201

Minimum

1.E+02

1.E+03 1.E+04 1.E+05 1.E+06

1.E+07 1.E+08

1.E+09

1.E+10

1.E+11

Span (Hz)

Figure 3. The user-settable parameter, frequency points, begins to determine the

boundaries of the time record length and frequency span operating region

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In addition to the time record length limits, there are limits to the allowable

range of spans. These are represented as vertical lines on the operating region

graphs (Figure 4). The upper span limit is set by the digitizer’s sample rate. For

the highest sample rate supported by the digitizer this boundary may be further

limited by the analog performance of the digitizer’s front-end. To zoom in on a

signal of interest by reducing the span, traditional VSA instrumentation reduces

the effective sample rate through the use of decimating ﬁlters while keeping

the ADC at full rate. This technique allows for maximum alias protection. Unlike

traditional VSA instruments, the Acqiris digitizers have no decimating ﬁlters.

To compensate for this shortcoming, decimating ﬁlters have been built into the

89600 VSA software. The maximum amount of decimation allowed by the 89600

VSA software sets the minimum span for any given digitizer sample rate.

The operating region depicted in Figure 4 is determined by constraints imposed

by both time record length and span. The Acqiris digitizers support many sample

rates. For each sample rate, the operating region shifts slightly on the operating

region graph. As the sample rate decreases, the operating region shifts slightly

up and to the left. So, for any given digitizer, there will be a family of overlapping

operating regions, one for each supported sample rate.

In general, these regions would be the same for every digitizer that supports a

given sample rate. The only difference is when the maximum span at the maxi-

mum sample rate is limited by analog performance of the digitizer’s front-end

rather than just by the sample rate.