Microwave Journal

New PCIe Digitizers Offer 10 GSPS and High Resolution

March 13, 2023

Two new PCIe Digitizer cards from Spectrum Instrumentation enable 10 GSPS sampling rate, 12-bit vertical resolution and 12.8 Gbps data streaming capabilities. The cards boast the highest sampling rate and bandwidth in company history, creating a powerful package for engineers and scientists working with today’s most challenging GHz-range electronic signals. The one-channel M5i.3350-x16 and the two-channel M5i.3357-x16 feature front-end circuitry with over 3 GHz bandwidth and up to 16 Gb (eight GSamples) onboard memory. They also reach the fastest digitizer data transfer speeds over PCIe on the market. Using 16-lane, Gen 3 PCIe technology, data can be streamed over the bus at 12.8 Gbps. The data can be sent to PC memory for storage or directly to CPUs and CUDA-based GPUs for customized signal processing and analysis.

With 12-bit resolution, these digitizers offer a better dynamic range than most conventional test instruments. For example, they deliver 16× more resolution than many digital oscilloscopes, which typically use 8-bit analog-to-digital converters. The extra resolution allows measurements to be made with a better signal-to-noise ratio (SNR) and improved accuracy and precision.

The front-end circuitry offers programmable full-scale ranges from ±200 mV to ±2.5 V together with variable offset. Acquisitions can be made in single-shot or multiple-waveform recording modes. To help capture the most elusive signals, a host of trigger modes are available for use on the channels or external trigger inputs. The modes include conventional edge triggering, along with more sophisticated methods such as Window, Re-Arm, Or/And (logical), Software and Delay. Installing the cards into a suitable PCIe slot can turn almost any PC into a powerful measurement tool. This opens the door for anyone wishing to use the latest CPU and GPU hardware for signal processing and analysis.

The new cards come with a five-year product warranty and all the tools necessary to use them in a PC running either a Windows or Linux operating system. A software development kit is provided, so that the cards can be programmed with almost any popular language including C, C++, C#, Delphi, VB.NET, J#, Python, Julia, Java, LabVIEW and MATLAB. Alternatively, the company offers SBench 6 Professional. This powerful measurement software provides full card control, along with a host of data display, analysis, storage and documentation capabilities.

Figure 1

Figure 1 Response of a 1 GHz QPSK-modulated signal sampled at 10 GSPS.

Figure 2

Figure 2 I/Q, FFT and trajectory plot of 12.8 Gbps data stream.

A low-cost option, M5i.33xx-spavg, is available for summation averaging using onboard FPGA technology. Averaging reduces unwanted signal noise while enhancing the dynamic range and SNR. The cards can average signals at a rate of up to 15 million events per second, making them one of the fastest signal-averaging solutions on the market.

The new M5i digitizers are suitable for many applications. One such example is testing high speed communications channels using quadrature modulation. Figure 1 shows an example of the acquisition of a 1 GHz carrier modulated by a 40 Mbaud quadrature phase shift keyed (QPSK) signal displayed using Spectrum Instrumentation’s SBench 6 measurement software.

Twenty microseconds of the QPSK signal were acquired at 10 GSPS. The FFT of the signal has a peak at the carrier frequency of 1 GHz. Modulation sidebands spaced at 160 MHz extend symmetrically from the carrier frequency. The signal components show significant energy out to 2 GHz and the harmonic of the carrier at 3 GHz. The bottom center trace shows the details of the sideband structure. The 160 MHz spacing of the modulation sidebands is due to the sampling in the transmitter. This is shown in the period between phase breaks in the time domain waveform in the upper right trace, as measured by the cursors. Cursor readouts and measurements of the signal frequency, amplitude and mean value appear in the info panel on the left of Figure 1. The narrowest burst in the top center trace highlights the 40 Mbaud data rate. The modulating signals are bandlimited to 20 MHz as seen in the expanded FFT in the lower right trace of Figure 1.

Transferring the data at up to 12.8 Gbps via the PCI Express x16 interface to a CPU or CUDA-GPU for custom processing creates the opportunity for further analysis, as shown in Figure 2. The demodulated in-phase (I) and quadrature (Q) signals on the top and their FFTs on the bottom show the effects of 20 MHz raised root cosine low-pass filtering that has been applied to the signals. The cross plot of the I and Q components on the far right of the display in Figure 2 produces the trajectory diagram highlighting the transitions between digital states.

Spectrum Instrumentation GmbH
Grosshansdorf, Germany