6 GHz True RMS Power Meter

with Bus-Powered USB Connectivity

Overview

The National Instruments USB-5680 is a 6 GHz true RMS (root-mean-

square) power meter that features high measurement accuracy and wide

dynamic range. As a true RMS power meter, the NI USB-5680 is ideal

for measuring the power of continuous wave (CW) signals. In addition,

it offers better than ±0.18 dB of linearity across all frequency ranges and

all power levels. This functionality, combined with a flexible API, makes

it ideal for measuring path loss in automated test applications. In

addition, its small size (less than 9.6 cubic in.) frees up valuable rack

space without sacrificing performance. One of the biggest benefits of the

USB-5680 is its USB connectivity. Powered solely from the USB cable, it

consumes only 100 mA of current. Thus, you can use this power meter in

both production test and field applications with a laptop. Moreover, USB

connectivity helps you easily integrate the power meter with PC and PXI

systems in an automated test environment.

Architecture

The USB-5680 RF power meter features a dual-path architecture to

achieve 63 dB of dynamic range. This architecture improves power

measurement accuracy by ensuring that the diode sensors are used in

their most linear region. A block diagram of the USB-5680 architecture

is shown in Figure 1.

As Figure 1 shows, the first measurement range is from -5 to +23 dBm

and the second is from -40 to -5 dBm. This accounts for a combined

dynamic range of -40 to +23 dBm with a single power head.

• True RMS power measurements

• Diode power meter

• -40 to +23 dBm power range

• 50 MHz to 6 GHz frequency range

• 10 and 100 Hz typical

channel bandwidth

• ±0.13 dB accuracy at <+18 dBm

• ±0.18 dB accuracy at

≥+18 dBm

• Internal zeroing capability

• <3 percent sensor linearity

• Standing wave ratio <1.2 to 6 GHz

• 100 mA typical power consumption

• USB bus connectivity

• N-type connector

Operating System

• Windows Vista/XP/2000

Recommended Software

• LabVIEW

Driver Software (included)

• NI-568x

Calibration

• Gain and offset self-calibration

• 1-year external calibration cycle

USB

Microprocessor

ADC

Averaging

Pre-Amp

Averaging

Pre-Amp

Detector B

(-40 to -5 dBm)

(-5 to +23 dBm)

Detector A

6 dB

Attenuator

6 dB

Splitter

27 dB

Attenuator

10 dB

Attenuator

DC Block

Input

Figure 1. Block Diagram of the NI USB-5680

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and search for USB-5680 Specifications.