Rf vector signal analyzer – Atec Keithley-2820 User Manual

Page 4

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r R

High accuracy and Repeatability
The Model 2820’s RF input circuitry was designed to combine simplicity

with high accuracy and repeatable performance. In R&D applications, this

helps engineers determine design stability and performance consistency.

In production test, high measurement accuracy and repeatability provide

confidence in the quality of the devices tested. It also allows minimizing

measurement guard bands, which helps increase product yields. Significant

signal analysis performance specifications include:
• Absolute amplitude accuracy of ±0.6dB (typically ±0.2dB) with a 0dBm

signal up to 2GHz

• ±0.2dB relative amplitude accuracy (display fidelity)
• ±0.15dB (typically ±0.07dB) amplitude repeatability
The instrument’s absolute amplitude accuracy can be increased by using an

external power meter to correct for frequency response variations of the

analyzer and test system cables connected to the DUT test fixture interface.

A power correction table feature in the Model 2820 allows users to enter

amplitude offset values vs. frequency to correct all power value readings.

This simplifies test system calibration and reduces operator errors.

Ultra-fast Measurements
The Model 2820 was designed to make fast measurements without compro-

mising accuracy. Its high speed DSP controls the instrument hardware and

runs all measurement operations. For example, when using the traditional

spectrum analysis function, the instrument can sweep 650MHz/s in a 1kHz

bandwidth, which is more than 800 times faster than traditional spectrum

analyzers. And, because the Model 2820 has an all-digital IF architecture,

it maintains its high speed over a wide range of resolution bandwidths and

frequency spans. For example, in R&D product verification testing, this can

reduce the time required for spur searching measurements from several

weeks to a few days, significantly reducing time to market.

µP-based

Keithley

Model 2820

DSP-based IF

Competitor

Analog

circuit-based IF

90% of measurements

1000

100

0.1

0.01

0.001

0.0001

0.00001

0.000001

100

1,000

10,000

100,000

1,000,000 10,000,000

Resolution Bandwidth (Hz)

Trace Updat

e Rat

e (GHz/s)

Trace Update Rate vs. RBW

The Model 2820’s DSP-based architecture allows it to provide

unprecedented measurement speeds. This graph shows that the

spectrum analysis measurement speed (measured in GHz frequency

span per second) of the Model 2820’s DSP-based IF is up to 800

times faster than a typical competitive spectrum analyzer which uses

both microprocessor-based and traditional analog IF technologies.

The Model 2820’s RF circuitry was optimized for speed and accuracy. The

RF input section employs a patent-pending DDS (Direct Digital Synthesis)

synthesizer design to switch frequencies in 1.3ms using List or Sweep

modes and in 3ms using a remote SCPI command.
An electronic attenuator is used to change the Reference Level to measure

rapidly over a wide dynamic range. This hardware approach has the added

benefit of superior measurement repeatability over millions of cycles in

production environments, unlike relatively slow mechanical attenuators,

which gradually degrade after a few thousand cycles. Flexible trigger and

synchronization choices further enhance measurement speed.

2820

Trig In

Sync Out

Series

2900

DUT

Trig In

Sync Out

RF Connections

The Model 2820’s trigger input and sync output connections simplify

synchronizing its operation with that of other test instruments,

such as Keithley Series 2900 RF Signal Generators, in high speed

measurement applications.

The Model 2820’s channel Power List mode supports measuring

power at multiple frequencies rapidly and flexibly.

The Model 2820 captures signal data and stores it in its waveform memory,

allowing the DSP to make measurements on one common set of data. Only

measurement results are passed to the host microprocessor and to the PC,

which ensures dramatically better measurement speed and greater consisten-

cy of measurement results when compared with measurements made with

instruments using microprocessor-based architectures. For example, six

signal measurements can be completed on a GSM signal in 24ms and seven

measurements can be completed on a W-CDMA signal in 60ms. Switching

between measurement types takes from 8ms to 29ms.

2820

RF Vector Signal Analyzer

400MHz to 4GHz or 6GHz