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What is a frequency response analyzer?
A frequency response analyzer (FRA) is a high-precision measuring instrument used to analyze components, circuits, and systems (called the device under test or DUT) in the frequency domain. An FRA typically generates a sine signal and injects it into the component, circuit, or system under test. This signal is measured at the injection point using one of the input channels on the FRA (usually channel 1). The injected signal passes through the DUT, and the frequency response analyzer simultaneously measures the same signal at a second reference point (usually the system output, using channel 2). Using a sine wave allows the frequency-domain behavior (frequency response) of the system to be determined.
Frequency response analyzer and DUT
Connection of
The diagram on the left illustrates the basic overview of connecting an FRA to a DUT, with the signal generator and reference channel (CH1) connected to the DUT input and CH2 connected to the DUT output.
This connection method can determine the frequency-domain behavior (also known as frequency response) of the DUT. The DUT's response over a specific frequency range can be determined by performing a "sweep", which involves stepping the injected frequency across a user-preselected frequency range.
Frequency Response Analyzer Block Diagram
Once the test signals reach the input of the frequency response analyzer, they are conditioned by N4L's proprietary ranging circuit and then digitized by a high-linearity ADC. After digitization, the data is passed to an FPGA/DSP for discrete Fourier analysis. The DFT acts as a "notch filter," extracting only the injected signal frequency while all other frequencies are suppressed. For example, if the FRA generator injects a 1kHz signal into the circuit, the frequency response analyzer uses the DFT process to extract only the 1kHz component from the signal passed to the FPGA.
Without the DFT process, the signal digitized by the frequency response analyzer would also contain noise. The DFT process provides excellent selectivity and a very high (120dB) dynamic range.
The DFT outputs of CH1 and CH2 are compared, including amplitude and phase shift. The absolute gain (CH2/CH1) is converted to a dB value, and the dB gain and phase shift (in degrees) are displayed.
How can I use a frequency analyzer for my development work?
A frequency response analyzer should be considered as important as an oscilloscope for any hardware test bench; it is a primary design tool that plays an important role on any hardware engineer's test bench. It is important to remember that N4L FRAs are precision instruments with calibrated inputs and provide measurement accuracy typically seen only in metrology.
FRA can be used to characterize the gain/phase response of input filter circuits, determine the AC signal behavior of transistors, determine whether a servo motor control system is stable, and enable engineers to determine the transfer function of a device or subsystem. These are just a few of the thousands of applications in which a frequency response analyzer can be used.
Application examples
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Control loopStabilityAnalysis | TransistorPerformanceAnalysis | Filter design | Audio amplifierDesign | OptocouplerEvaluation | Coaxial cableFrequencyResponse | LDO regulatorEvaluation | Signal transformerPerformanceEvaluation | CrosstalkTest | RFI/EMC filterDesign |
Wide-bandwidth frequency response analysis combined with versatile measurement
In today's world, engineers from different application fields need ever-increasing speed, flexibility, and measurement accuracy. The PSM series is a new generation of versatile frequency response analyzers that delivers leading performance in a variety of modes without compromising accuracy or the extra cost typically associated with such flexible instruments. Newtons4th utilizes innovative modern technology and unique circuit designs in our instruments to achieve such high accuracy without excessive cost.
PSM series instruments not only provide traditional frequency response measurement, but can also be combined with an impedance analysis interface to form a high-precision impedance analyzer. For the PSM3750, this solution is capable of impedance analysis up to 50MHz.
Other features include an oscilloscope function (PSM3750 + SFRA45) as well as power analyzer, harmonic analyzer, and vector voltmeter modes.
Full frequency response analyzer series comparison table
Standard
Options
Not available
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| Basic accuracy | 0.02 dB | 0.02 dB | 0.01 dB | 0.01 dB |
| Phase accuracy | 0.025° | 0.02° | 0.02° | 0.025° |
| Frequency range | 5 Hz ~ 45 MHz | 10uHz ~ 1 MHz | 10uHz ~ 35 MHz | 10uHz ~ 50 MHz |
| Measurement | Real-time DFT | Real-time DFT | Real-time DFT | Real-time DFT |
| IAI impedance analysis option available |  |  | | |
| IAI impedance analysis basic accuracy | | 0.1% | 0.1% | 0.1% |
| LCR active head option available | | | | |
| LCR active head accuracy | | 0.2% | 0.2% | |
| No. of channels | 2 | 2 | 2 | 2 or 3 |
| True RMS voltmeter |  | | | |
| Oscilloscope | | | | |
| Isolated generator | | | | |
| Isolated inputs | | | | |
| Harmonic analyzer | | | | |
| Power Analyzer | | | | |
| Maximum input voltage | 10Vpk | 100Vpk | 10Vpk | 500Vpk |
| No. Range | 9 | 9 | 9 | 16 |
| USB memory port | | | | |
| LAN port | | | | |
| GPIB port | | | | |
| RS232 port | | | | |
| Real-time clock | | | | |
| 19-inch rack mount option | | | | |
| Internal memory | 1000 records | 8000 records | 8000 records | 16000 records |
| Dimensions exclude feet (H x W x D mm) | Approx. 305 x 230 x 45 | 170 x 350 x 250 | 170 x 350 x 250 | Approx. 92 x 215 x 312 |
| Weight (instrument) | 2.7 kg | 4 kg | 4 kg | 3.3 – 3.5 kg |
