Measurement accuracy and signal integrity have replaced bandwidth as important factors in the evaluation of oscilloscopes by vendors and customers.
While bandwidth is a significant factor, especially in high-speed applications, the primary task of an oscilloscope is to capture and analyse fast serial and optical signals with precision and accuracy.
Representing a signal of interest as accurately as possible involves the fundamental design of the instrument, probe architecture and connectivity accessories, and parameters beyond bandwidth including rise time, sample rate and jitter noise floor.
Market Drivers - The need for better signal integrity
High speed signals are susceptible to signal integrity issues because they involve very fast edges and very narrow unit intervals or bit times. As the data rate for a communication link, the UI narrows and the rise time of the signal decreases.
Multiple signal integrity issues introduced as a transmitted signal makes its way to the receiver complicate the matter further. These signal integrity issues can include attenuation as the signal travels across a circuit board or from the Si die to the package pins and onto the circuit board.
Losses in PCB material such as FR-4 increase with trace length as well as with data rate. As signal amplitude shrinks, noise and reflections are becoming a bigger factor.
With the push to 4 x 25G (100GbE) Ethernet, designers need the ability to test signals with bit rates as high as 32 Gb/s. High-speed FPGA and wideband RF are also pushing the limits.
Tektronix presents the DPO/DSA73304D oscilloscopes with highly accurate measurement capabilities for these high-end applications.
Key features of DPO/DSA73304D oscilloscopes:
- IBM’s 8HP silicon delivers excellent signal acquisition performance and analysis capability
- 130 nanometer SiGe bipolar complementary metal oxide semiconductor (BiCMOS) process offers 2x performance over the previous generation with an FT switching speed of 200 GHz
- SiGe technology leverages highly reliable and mature fabrication processes, offering performance levels comparable to exotic materials such as Indium Phosphide (InP) and Gallium Arsenide (GaAs)
- SiGe BiCMOS provides access to high-speed bipolar transistors on the same die as standard CMOS, offering high performance as well as large-scale integration
- New 33 GHz, 100 GS/s front end using SiGe BiCMOS contains pre-amplifiers for 2 channels and a single 100 GS/s track and hold IC
- Integrated pre-amps and track and hold functions in a single package improves the channel to channel matching and reduces interleave distortion
- Reduced number of components and interfaces required reduces noise and timing uncertainties, increasing ENOB performance
- Large offset range and termination capability in the front end design makes accurate measurements easy for signals with large DC offsets or DC bias terminations
- Allows designers to capture real signals with uncompromised acquisition on all four channels and capture more signal details with industry-leading waveform capture capability
- Automates setup, acquisition and analysis of high-speed serial data signals with a toolset engineered to deliver faster design and compliance testing
- Up to 33 GHz and 100 GS/s on 2 channels with >20 GHz and 50 GS/s on all 4 channels
- Less than 9 ps rise time (typical 20/80)
- Lower than 0.56% vertical noise with ≥5.5 effective bits
- Over 30 customisable application-specific software analysis packages
Rise time, sample rate and bandwidth are important specifications in oscilloscopes that can affect measurements.
Two oscilloscopes that have the same bandwidth performance can have very different rise times, amplitude and phase response. So, knowing only the bandwidth of an oscilloscope will not reliably reveal its measurement capability. Specifying rise times from a calculation can also be inaccurate.
The most reliable way to know the rise and fall time response of an oscilloscope is to measure it with an ideal step signal that is much faster than the oscilloscope.
In the case of the DPO/DSA73304D, the rise time of 9 ps was determined using this method. A good rule of thumb for the signal to scope rise time ratio is 2x or >18 ps, which is the specified rise time for a 28 Gb/s SerDes used in today’s fast FPGA designs.
The real-time sample rate of the scope is another key performance consideration, important because faster sample rates lead to greater waveform detail. The DPO/DSA73304D delivers class-leading sample rate performance with interleaving techniques that keep spurious high frequency effects to a minimum using an 8-way track and hold methodology. Oscilloscopes must also have sufficient bandwidth to capture the higher frequency components, and therefore show signal transitions accurately.
Key capabilities of the new DPO/DSA73304D oscilloscopes:
- Combines industry-leading signal integrity and timing precision in a real time scope, enabling superior accuracy
- Helps discover critical signals of interest with highly accurate acquisition system featuring reliable SiGe technology used in oscilloscope and probe
- Captures precise signal events needed to evaluate high-speed signals with comprehensive trigger system
- Searches through records with high sample rate to identify critical occurrences/errors for system validation
- Analyses critical measurement results quickly with high signal to noise ratio in a 30+ GHz oscilloscope
- Provides high-sensitivity, low noise measurement results that facilitate accurate characterization of high speed optical, energy and serial data measurements
Tektronix oscilloscopes are available from TekMark Australia .