Keysight Basic Instruments (May-July 2017)

Perform automatic frequency response analysis (Bode gain and phase plots) with your oscilloscope

Years ago, engineering students created Bode plots by hand for everything from finding theoretical poles and zeros to drawing the plot. In the Electrical Engineering (EE) lab, students didn’t have analyzers to automatically perform tasks like verifying the frequency response of a passive or active filter. The solution was to take multiple VIN, VOUT, and Δt measurements on an oscilloscope while changing the input sine wave frequency on a function generator. After making 15 or 20 measurements, students would have enough measured data points to convert to gain (20LogVOUT/VIN) and phase shift (Δt/T x 360). Students could then plot the results alongside the theoretical graph for comparison. That tedious process must have changed by now, right? Yes and no. Most engineering students today—and those who have moved on to amplifier design and digital control—use MATLAB to plot theoretical results. And the test industry offers a broad range of frequency response analyzers (FRA) and vector network analyzers (VNA) that create gain and phase plots automatically. But FRAs and VNAs are specialized instruments that are not often seen in universities, mostly due to their cost. Schools will usually purchase a typical student bench consisting of an entry-level two-channel oscilloscope, function generator, digital voltmeter, and power supply for under $2K, keeping in line with their limited lab budgets.

Save money with oscilloscopes that combine multiple instruments into one

Keysight’s new InfiniiVision 1000 X-Series family of low-cost oscilloscopes addresses educator’s needs and budget constraints by giving them multiple instruments in one oscilloscope, including a digital voltmeter, frequency response analyzer (select models) and WaveGen function generator (select models). The baseline model is $449 (USD), but for about $200 more, you can get a model with a built-in WaveGen function generator and frequency response analysis. To use the 1000 X-Series to make measurements on a passive bandpass filter (Figure 1), you connect the generator output to VIN and also probe VIN and VOUT with channel 1 and channel 2 of the oscilloscope, respectively. To help you make the proper connections, the FRA setup menu displays a block diagram (Figure 2). You can also define which of the oscilloscope’s input channels is probing VIN, which channel is probing VOUT, the minimum and maximum test frequency, and test amplitude. The oscilloscope executes a one-time test, sometimes called a “sweep.” Not only is this one of the most easy-to-use FRAs on the market, but it is also one of the least expensive. Frequency response analysis comes standard on 1000 X-Series oscilloscope models with the built-in function generator. And performance is not sacrificed either; Using a proprietary measurement algorithm, the 1000 X-Series can achieve up to 80 dB of dynamic range based on a 0 dBm (224 mVrms) input. The FRA option is also available on Keysight’s higher performance 3000T X-, 4000 X-, and 6000 X-Series oscilloscopes with additional advanced features, including test amplitude profiling, single frequency test mode, and tabular results view.

– Up to 1,000,000 waveforms/sec update rate

– MegaZoom IV responsive, uncompromised smart memory

• Multiple instrument functionality
• Upgradable: bandwidth, MSO, serial analysis, built-in WaveGen function generator, or digital voltmeter and counter
• Low-cost, 3-slot unit with 6½ digit DMM and built-in signal conditioning
• Choose from 8 plug-in modules, up to 120 1-wire (60 2-wire) channels or 96 cross points
• 34972A has built-in Web interface
• 6½ digit 7½ digit performance
• Graphical capabilities such as trend and histogram charts
• Measure very low current, 1 µA range with pA resolution, allowing measurements on very low power devices.
• Auto calibration to compensate for temperature drift
• Basic measurements: DCV, ACV, DCI, ACI, 2- and 4-wire resistance, frequency period, continuity, diode, temperature, capacitance