Frequency and Microwave
Figure 2: The in-phase (I) and quadrature (Q) components of the demodulated signals. Cross plotting the I and Q signals yields the state transition or trajectory diagram.
to read and write data into the device; the signals are clock, strobe, and data. The data signal is shown in the figure. The acquired data signal is shown in the upper left trace. A horizontally expanded view of the signal is shown in the lower left trace. The FFT spectrum of the data signal is shown in the right- hand trace. As expected, the spectrum has a Sin(x)/x envelope due to the pulse-like nature of the digital signal. The device is clocked at 333 MHz. As the name implies, DDR memory operations occur at twice the clock rate. The nulls in the spectrum occur at 666 MHz and integer multiples of that frequency. The
Application 2: Measuring RADAR pulses
A perfect fitting RF application for the M5i digitizers is radar analysis. Figure 3 shows an example of acquiring a 1 GHz, phase modulated radar pulse.
The radar pulse is acquired with the maximum sampling rate of 10 Giga Samples per second (GS/s) shown on the Spectrum Instrumentation’s SBench 6 measurement software. The phase modulation is a bi- phase Barker code intended to improve the range resolution of the radar. They are a sequence of numbers of different lengths of +1 and -1. The acquired data was transferred to MATLAB where the phase demodulation was performed, and the demodulated signal imported back into SBench6. A software development kit (SDK), that includes drivers that allow common third-party analysis software like LabView and MATLAB to control and communicate with the digitizer, is included. The digitizer also can transfer the data at up to 12.8 GB/s via the PCI Express x16 interface to the PC system or do a direct transfer to a CUDA GPU for custom processing. These interfaces provide the ability for further advanced analysis.
The Fast Fourier Transform (FFT) of the acquired signal shows the frequency spectrum of the signal. As expected, it has a peak at the carrier frequency of 1 GHz. A horizontal zoom expansion of the FFT at the carrier frequency shows the spectral broadening due to the phase modulation. In this application the long record length of up to 8 GSamples is also very useful to study tracking histories of up to 800 ms at the 10 GSps maximum sampling rate. The measured pulse has a duration of 20 ms and, at a 10 kHz pulse repetition frequency of 10 kHz, about 8000 such pulses can be acquired in each record.
www.cieonline.co.uk.
Figure 3: A 1 GHz phase modulated radar pulse (upper left) with the demodulated phase information (lower left). The frequency spectrum of the pulse (upper right) and a horizontally expanded view of the spectrum (lower right).
Application 3: Analysing DDR 2 memory data signals
High speed digital physical layer signals can also be acquired by the M5i.33xx-x16 series digitizers. The bandwidth of a digital signal is dependent on the rise time of the pulses which is a function of the clock rate. The general rule of thumb
Figure 4: The data signal for a DDR2 memory has a complex structure. The FFT spectrum shows significant energy out to about 3 GHz.
is that the measurement bandwidth of the measurement system should be five times the clock frequency of the digital system. You can see this in the example shown in Figure 4 showing the acquisition and analysis of a double data rate (DDR 2) memory data signal. DDR memories use three digital signals
spectrum shows considerable energy out to about 3 GHz.
The range of applications for the M5i.33xx-x16 series digitizers are very broad. The three examples shown offer insight into the possibilities that exist.
www.spectrum-instrumentation.com
Components in Electronics
June 2023 31
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