Technologies like terabit optical data communications, next generation digital bus standards, high speed I/O and new wireless standards are demanding higher bandwidth and more accurate measurements in multi-channel test systems.
Similarly, emerging millimeter-wave applications are demanding wider bandwidths. For example, 802.11ay demands about 4 GHz of bandwidth in the 60 GHz band. High signal integrity is needed for waveform quality measurements such as Error Vector Magnitude (EVM), especially over multi-GHz of signal bandwidth with higher-order modulation schemes.
Therefore, Keysight has designed custom ASICs to power hardware bandwidth of 110 GHz in an oscilloscope with more signal integrity than any other oscilloscope in its class. This technology has been optimized to 13 GHz providing a new family of oscilloscopes to advance the world of high-speed digital design, wireless, and RF. Keysight’s Infiniium UXR-Series oscilloscopes are the first oscilloscopes to achieve greater than 40 GHz of bandwidth without frequency interleaving, a process which adds noise and distortion to your signal under test.
Journey of a Signal
To understand the new technology within Keysight’s new oscilloscopes, let’s follow the journey of a signal through a UXR (Figure 1).
First, the signal will enter through the channel. A challenge in developing a high bandwidth oscilloscope is the channel. Reflections in the channel can cause measurement inaccuracies. Standard 3.5 mm connectors are only accurate below 40 GHz. Therefore, 33 GHz models and below use robust 3.5 mm connectors, Keysight’s traditional AutoProbe II interface to support traditional SMA connections, and Infiniium probes the engineer may already have on their lab bench. For 40 GHz to 70 GHz models, Keysight uses 1.85 mm technology which is a little more delicate, but extends bandwidth capabilities. To support 80 GHz and above, Keysight uses 1 mm connectors, the industry standard for supporting millimeter wave technology up to 110 GHz. These connectors are more fragile and require adaptors to connect traditional probes, but if you are testing at these bandwidths, it is more likely you will connect cables directly to the 1 mm input, rather than use hand-held probes, to maintain signal integrity.
Figure 1: Simplified block diagram of UXR oscilloscope.
From the front-end connector, the signal is sent into a mechanical attenuator. Then, the signal is sent directly into the pre-amplifier, the first component on the front-end module. While this sounds very simple, this is one of the key distinctions between UXR oscilloscopes and other high bandwidth oscilloscopes. The front-end module consists of a Keysight proprietary Indium Phosphide (InP) chipset protected from noise and interference with faraday cage technology. It is custom designed to power 110 GHz signals while keeping noise to a minimum (Figure 2).
Figure 2: The front-end module of a 110 GHz UXR oscilloscope.
This is a key distinction because the hardware can support the full bandwidth of the oscilloscope. Other high bandwidth oscilloscopes must use frequency interleaving to achieve their bandwidth because the chip technology within the oscilloscopes are limited. Frequency interleaving can double or even triple an oscilloscope’s bandwidth beyond the raw hardware capability of its chip sets. The trade-off is additional circuitry which adds significant noise and distortion to measurements which is then amplified by the pre-amp. Additionally, digital signal processing is used to stitch the signal components back together which can add more noise to the signal. This all happens in the front end of the oscilloscope before acquisition begins.
With a pre-amp able to accept 110 GHz signals without attenuation, the UXR can forego frequency interleaving, preserving the signal under test. One of the trade-offs to designing hardware to support higher bandwidth without frequency interleaving is time-to-market. However, the improvement in performance is well worth the design effort.
After the signal passes through the attenuator and the pre-amp, the signal is sent both to a 256 GSa/s sampler (also designed uniquely for the UXR with InP) and a trigger comparator. The 256 GSa/s high-speed sampler slows the signal down for the rest of the system in a process called time interleaving. Unlike frequency interleaving, time interleaving is carefully controlled with the oscillator board. Now acquisition begins. The signal enters an array of 10-bit ADCs - each ADC chip accepting 64 GSa/s. 10-bit ADCs provide 4x the vertical resolution of 8-bit ADCs.
The analog signal, now converted to digital information, is sent to Keysight’s new memory controller which reads and writes to a modern 2.5D memory storage device which enables 2 Gb of deep memory. Remember the trigger comparator? That has also sent trigger information to the memory controller. The memory controller enables filtering, de-embedding, triggering, and other advanced hardware features. It even has a bus for plotting the waveform to reduce the work done in the FPGA speeding up the performance of the oscilloscope. The memory controller sends all this info to the FPGA which communicates to the CPU over PCI express to display your signal and measurements on the screen of your oscilloscope.
Each 110 GHz channel has its own acquisition board, so you always have access to full bandwidth and memory depth on every channel.
This oscilloscope design has enabled new industry-bests.
The UXR provides:
- Four full bandwidth channels with up to 110 GHz of bandwidth
- As low as 210 uVrms of noise at 10 mV/division
- Only 25 fs rms of intrinsic jitter at 1us/div
- Less than 10 fs rms of inter-channel intrinsic jitter
- Up to 6.8 effective bits
Why Does Any of This Matter?
For emerging millimeter-wave applications up to 110 GHz, high-performance digital oscilloscope technology offers engineers an additional tool to gain insight when analyzing wide-bandwidth millimeter-wave signals. Directly digitizing millimeter-wave signals and post-processing them with application software, enables engineers to directly measure wideband millimeter-wave signals, complementing the more traditional approach of using an external downconverter with a lower-bandwidth oscilloscope. The UXR’s accuracy with up to 6.8 effective bits enables wideband EVM measurements to be performed, like 802.11ay, even at higher-order modulation schemes.
As anyone in the high-speed digital industry can tell you, test margins are decreasing as new generations of legacy technologies become the standard. Design cycles are shorter than ever and compliance is becoming more difficult to pass as the limits of existing hardware are reached. Previously, there was so much time between bit transfers, set up and rise time tests were only required to pass specification. Now, passing compliance requires not only strict mask test validation, but also pre- and post-channel equalization. Millivolts of noise can make the difference between passing or failing compliance. The UXR’s signal integrity reduces the risk of failing compliance due to excessive oscilloscope noise and jitter. With a noise floor as low as 210 uVrms at 10mV/division, and only 25 fs of intrinsic jitter, eyes will be wider and you can pass compliance tests with more confidence.
In terabit and optical research, achieving next-generation technology breakthroughs have been prohibited by limited test equipment. Reaching higher modulation standards than ever before requires measurement systems with extreme signal integrity, high bandwidth, and multiple channels to decipher complete coherent receiver designs. Daisy-chained single channel instruments can be cost prohibitive and highly inaccurate. Inter-channel jitter between daisy chained measurement devices can impede the ability to view signals clearly. Four high bandwidth channels with only 10 fs of inter-channel intrinsic jitter enable optical measurements that could not be made before.
The UXR was designed piece by piece with the intention of enabling future research in a host of different applications with new industry-best specifications. Keysight’s new technology blocks enable the UXR to revert to traditional, clean oscilloscope design practices without frequency interleaving thus, increasing signal fidelity in every category. For additional information, visit www.keysight.com/find/UXR.