A single one can destroy a signal, but predictions with validated models can be made.
An ideal digital interconnect is a lossless transmission line with characteristic impedance and phase delay flat over the signal bandwidth and termination resistors equal to the characteristic impedance. In such interconnect, bits generated by a transmitter would flow seamlessly into the receiver with no limits on the bit rate. Such a utopian transmission line exists only in our imaginations and textbooks. The physics of our world prohibit it. One way to describe “what happens to the signal on the way to a receiver?” is to use the balance of power that can be written for the passive interconnect as follows:
P_out = P_in - P_absorbed - P_reflected - P_leaked + P_coupled
This is frequency domain over the bandwidth of the signal.1 P_out is the power delivered to the receiver, and P_in is the power delivered by transmitter to the interconnect. All other terms in the balance of power equation describe the signal distortion. The formula above expresses all we need to know about the interconnects. (It should be “cast in granite.”). As they say, “a formula is worth a thousand words,” almost literally in this case. To understand it, imagine the interconnect system as a multiport with the transmitter at port 1, receiver at port 2 and multiple other ports for links coupled to the link connecting port 1 and 2 and terminations to real impedance (not necessarily identical at all ports) – something like this below, together with the definition of waves and scattering parameters (or S-parameters):
Fresh off its inaugural meeting, the PCBAA gets legislative good news. What’s next for the organization that wants to rebuild US production?
In early May the Printed Circuit Board Association of America, or PCBAA, held its first annual meeting, at which they shared progress on their overarching goal, which is to advance US domestic production of PCBs and base materials.
Coinciding with that meeting came an announcement from a pair of US legislators that they had introduced a bill to incentivize purchases of domestically produced PCBs, as well as industry investments in factories, equipment, workforce training, and research and development.
The bill, known as the Supporting American Printed Circuit Boards Act of 2022, is said to be modeled on the CHIPS Act of 2021, a much-touted piece of legislation that earmarks more than $50 billion toward new onshore semiconductor fabrication plants.
Timing is everything, right?
Numerical analysis of defects in single bit and single symbol response.
Modeling and measuring digital serial interconnects is usually done in the frequency domain. That means the minimal and maximal frequencies (or bandwidth) should be defined before analysis or measurement begins. The data rate and rise time define the signal bandwidth, and the usual practice is to define the maximal frequency as either the inverse of the rise/fall time (or fraction of it) or as a multiple of the fundamental or Nyquist frequency.1 Such a simple bandwidth definition may work for some structures, but it may fail for others. Ultimately, an SI engineer must make the decision for a particular signal type and interconnect structure.1
Here we introduce a simple, practical way to identify the bandwidth with a numerical analysis of defects in a single bit (SBR) or single symbol response (SSR). It begins with a brief introduction into structure and spectrum for 6Gbps and 112Gbps signals. Then, it proceeds with analysis of defects in SBR and SSR introduced by the bandwidth deficiency for two practical cases. The bandwidth is defined by a model with an acceptable level of defects in either SBR or SSR.
Embedded passives are being deployed for commercial market applications.
Recent advancements in mobile technologies have exponentially increased demand for radio spectrum bandwidth. The rush of equipment for more RF applications is being deployed across the world, with 5G and millimeter wave (mmWave) communications expanding into the commercial space to take advantage of the wider bandwidth, higher data rates and low latency that these frequency bands offer. Cellular 5G and 6G, low Earth orbit (LEO), mid Earth orbit (MEO), geosynchronous communications networks, interconnected devices (internet of things), autonomous driving vehicles, defense and environmental monitoring are all driving these needs. The antenna and sensors necessary to manage the signals for these applications are similarly changing, becoming more sophisticated.
To ensure high-data-rate wireless connectivity, the broadband high-gain antennas necessary to manage high-frequency but lower-power signals are increasingly moving from dish and horn to flat-panel active electronically steered antennas (AESA) for beam forming and massive MIMO designs. In response, the RF industry has developed new integrated circuits, materials, processes and equipment to build devices to manage these mission-critical sensor applications.
To keep a good high-speed signal quality from driver to receiver on a PCB is not an easy task for designers.
Reducing signal degradation requires dielectrics with lower Dk and LT, more metal and conductors without rough surfaces.
At a trade show a few years ago, our Simberian booth was next to a booth with a very loud demonstration transferring 112Gbps over a distance of about one meter through cables. I don’t know how many terabytes of data they transferred during the show, but the demonstration equipment was noisy because of the industrial cooling equipment. I could feel the heat coming out of it. The devices were transferring data and not much else. How much energy is required to transmit data, and why is so much power dissipated into heat, I wondered.
PCB interconnects degrade digital signals. Signals may be reflected, coupled to other interconnects, or to power distribution structures or free space, but most important, conductors and dielectrics always absorb the signal energy and dissipate or turn it into heat. This article is about signal degradation due to the inevitable absorption and dispersion caused by dielectrics and conductors. How much energy does it take to transmit one bit of information, and where does this energy eventually go?