The USB Type-C brings a lot of protocols into one physical connector, but is there room for one protocol to handle all our IO needs? Mike Hoffman and Daniel Bogdanoff sit down with high speed digital communications expert Jit Lim to find out.
USB Type-C brings a lot of protocols into one physical connector, but is there room for one protocol to handle all our IO needs? Mike Hoffman and Daniel Bogdanoff sit down with high speed digital communications expert Jit Lim to find out.
0:00 This is Jit’s 3rd podcast of the series
1:00 We already have one connector to rule them all with USB Type-C, but it’s just a connector. Will we ever have one specification to rule them all?
2:00 Prior to USB Type-C, each protocol required it’s own connector. With USB TYpe-C, you can run multiple protocols over the same physical connector
3:00 This would make everything more simple for engineers, they would only need to test and characterize one technology.
3:30 Jit proposes a “Type-C I/O”
4:00 Thunderbolt already allows displayport to tunnel through it
4:30 Thunderbolt already has a combination of capabilities. It has a display mode – you can buy a Thunderbolt display. This means you can run data and display using the same technology
6:30 There’s a notion of a muxed signals
7:00 The PHY speed is the most important. Thunderbolt is running 20 Gb/s
7:15 What would the physical connection look like? Will the existing USB Type-C interface work? Currently we already see 80 Gb/s ports (4 lanes) in existing consumer PCs
9:20 Daniel hates charging his phone without fast charging
9:40 The USB protocol is for data transfer, but is there going to be a future USB dispaly protocol? There are already some audio and video modes in current USB, like a PC headset
11:30 Why are we changing? The vision is to plug it in and have it “just work”
12:00 Today, standards groups are quite separate. They each have their own ecosystems that they are comfortable in. So, this is a big challenge for getting to a single spec
13:15 Performance capabilities, like cable loss, is also a concern and challenge
14:00 For a tech like this were to exist, will the groups have to merge? Or, will someone just come out with a spec that obsoletes all of the others?
15:30 Everyone has a cable hoard. Daniel’s is a drawer, Mike’s is a shoebox
16:30 You still have to be aware of the USB Type-C cables that you buy. There’s room for improvement
17:30 Mike wants a world of only USB Type-C connectors and 3.5mm headphone jacks
18:30 From a test and measurement perspective, it’s very attractive to have a single protocol. You’d only have to test at one rate, one time
Wide bandgap semiconductors, like Gallium Nitride (GaN) and Silicon Carbide (SiC) are shaping the future of power electronics by boosting power efficiency and reducing physical footprint. Server farms, alternative energy sources, and electrical grids will all be affected!
Wide bandgap semiconductors, like Gallium Nitride (GaN) and Silicon Carbide (SiC) are shaping the future of power electronics by boosting power efficiency and reducing physical footprint. Server farms, alternative energy sources, and electrical grids will all be affected! Mike Hoffman and Daniel Bogdanoff sit down with Kenny Johnson to discuss in today’s electrical engineering podcast.
3:00 What is a wide bandgap semiconductor? GaN (Gallium Nitride) devices and SiC (Silicon Carbide) can switch on and off much faster than typical silicon power devices. Wide bandgap semiconductors also have better thermal conductivity. And, wide bandgap semiconductors have a significantly lower drain-source resistance (R-on).
For switch mode power supplies, the transistor switch time is the key source of inefficiency. So, switching faster makes things more efficient.
4:00 They will also reduce the size of power electronics.
6:30 Wide bandgap semiconductors have a very fast rise time, which can cause EMI and RFI problems. The high switching speed also means they can’t handle much parasitic inductance. So, today’s IC packaging technology isn’t ideal.
8:30 Wide bandgap semiconductors are enabling the smart grid. The smart grid essentially means that you only turning on things being used, and turning off power completely when they aren’t being used.
9:35 Wide bandgap semiconductors will probably be integrated into server farms before they are used in power grid distribution or in homes.
10:20 Google uses a lot of power. 2.3 TWh (terawatt hour)
NYT article: http://www.nytimes.com/2011/09/09/technology/google-details-and-defends-its-use-of-electricity.html
It’s estimated Google has 900,000 servers, and that accounts for maybe 1% of the world’s servers.
So, they are willing to put in the investment to work out the details of this technology.
11:50 The US Department of Energy wants people to get an advanced degree in power electronics. Countries want to have technology leadership in this area.
13:00 Wide bandgap semiconductors are also very important for wind farms and other alternative forms of energy.
Having a solid switch mode power supply means that you don’t have to have extra capacity.
USA Dept of Energy: If industrial motor systems were wide bandgap semiconductors took over, it would save a ton of energy.
14:45 A huge percentage of the world’s power is consumed by electrical pumps.
16:20 Kenny’s oldest son works for a company that goes around and shows companies how to recover energy costs.
There aren’t many tools available for measuring wide bandgap semiconductor power electronics.
19:30 Utilities and servers are the two main industries that will initially adopt wide band gap semiconductors
20:35 When will this technology get implemented in the real world? There are parts available today, but it probably won’t be viable for roughly 2-5 years.
21:00 Devices with fast switching are beneficial, but have their own set of problems. The faster a devices switches, the more EMI and RFI you have to deal with.
Spread spectrum clocking is a technique used to pass EMI compliance.
24:00 Band gaps of different materials: Diamond 5.5 eV Gallium Nitride (GaN) 3.4 eV Silicon Carbide (SiC) 3.3 eV
Learn about power integrity and signal integrity in this electrical engineering podcast. Power integrity will impact signal integrity, EMI, and EMC! We sit down with Kenny Johnson to discuss.
Hosted by Daniel Bogdanoff and Mike Hoffman, EEs Talk Tech is a twice-monthly engineering podcast discussing tech trends and industry news from an electrical engineer’s perspective.
How’s the impedance of your ground plane? Do you look at your power rails in the frequency domain? Mike Hoffman and Daniel Bogdanoff sit down with power integrity expert Kenny Johnson to discuss the latest trends and techniques for measuring power supplies in today’s electrical engineering podcast.
3:03 Power integrity is the study of the effectiveness of the conversion and delivery of DC power from the source to the gates on the IC.
3:45 If Moore’s Law holds out for another 600 years, we will have a computer that is capable of simulating every atom in the known universe.
4:35 Thermal hotspots were causing problems, so voltage levels started dropping
5:00 Kenny went to Amazon to look for a power integrity book. There were only 2-3 books a few years ago
Power integrity has been a thing since the 1930s
5:50 Product functional reliability is directly proportional to the power quality in a product.
We’re supplying a voltage to devices, but also current. So, this starts to look a lot like Ohm’s law.
A device has both power and a ground plane.
Power integrity pioneers include Istvan Novak and Ray Ridley and they talk about flat impedance power planes.
7:15 Flat impedance power planes – divide the supply power by the peak current, multiply it by your tolerance, you get a target impedance for your power planes.
If you can maintain a frequency flat impedance, you don’t see noise on your power supplies.
7:55 Think back to circuits 101, an inductor is open at a high frequency. And, a power plane is basically a big inductor. If you are, for example, writing high speed digital data to memory, it will be a problem.
8:40 When you look at boards, you see bypass capacitors to counteract the inductors
10:30 Experienced engineers use a lot of intuition when working out power distribution. Now, there’s a lot of localized power distribution.
Next generation mobile electronics 100-200 power supplies
12:25 There are redundant power supplies spread out across the device to help improve reliability. For example, there may be multiple converters that all power the same rail to help spread the loads.
The reason intuition is used is that a lot of people don’t have access to good simulation tools. They just have to use some rules of thumb and over-engineer the device to try to get reliability.
15:10 Kenny has a lot of patents. Our CTO Jay Alexander used to hold the record for most patents at the Colorado Springs site. Kenny has nearly 30 patents.
17:15 Kenny started as a probe designer, then got into power integrity.
Kenny recommends one by Bogatin about signal integrity, and a second edition called Signal Integrity and Power Integrity
18:35 SIPI labs – signal integrity and power integrity lab. Power integrity will affect your signal integrity, your EMI (electromagnetic interference) and your EMC (electromagnetic compatibility). (measure power integrity with a power rail probe)
So, the progressive companies have these SIPI labs. There are more advanced tools available.
20:10 Multiple papers say that power supply induced jitter is the single biggest source of data jitter in a digital system.
Kenny has some IOT development kits, and it’s easy to make them drop bits. Dropping bits will have an effect on battery life, performance, etc.
21:08 How to clean up a power supply? The majority of the time, it’s easiest to use a bypass capacitor. After you’ve looked at your supply in the time domain, look at it in the frequency domain. That will help you debug where the noise is coming from. And, if you know the frequency you are having trouble with, you can work backward into a bypass capacitor
22:42 There are some general rules that seem to apply to everything in electronics. Closer to the device is always better.
Next podcast – wide bandgap! The US Department of Energy will pay for some people to go back to university and get a degree in power engineering. Wide bandgap semiconductors have a huge potential to reduce energy usage.
Learn how PAM4 is allowing some companies to double their data rate – and the new challenges this brings up for engineers. (electrical engineering podcast)
Today’s systems simply can’t communicate any faster. Learn how some companies are getting creative and doubling their data rates using PAM4 – and the extra challenge this technology means for engineers.
Mike Hoffman and Daniel Bogdanoff sit down with PAM4 transmitter expert Alex Bailes and PAM4 receiver expert Steve Reinhold to discuss the trends, challenges, and rewards of this technology.
PAM isn’t just cooking spray.
What is PAM4? PAM stands for Pulse Amplitude Modulation, and is a serial data communication technique in which more than one bit of data can be communicated per clock cycle. Instead of just a high (1) or low (0) value, a in PAM4, a voltage level can represent 00, 01, 10, or 11. NRZ is essentially just PAM2.
We are reaching the limit of NRZ communication capabilities over the current communication channels.
2:10 PAM has been around for a while, it was used in 1000BASE-T. 10GBASE-T uses PAM16, which means it has 16 different possible voltage levels per clock cycle. It acts a bit like an analog to digital converter.
2:55 Many existing PAM4 specifications have voltage swings of 600-800 mV
3:15 What does a PAM4 receiver look like? A basic NRZ receiver just needs a comparator, but what about multiple levels?
3:40 Engineers add multiple slicers and do post-processing to clean up the data or put an ADC at the receiver and do the data analysis all at once.
PAM4 communicates 2-bits per clock cycle, 00, 01, 10, or 11.
4:25 Radio engineers have been searching for better modulation techniques for some time, but now digital people are starting to get interested.
4:40 With communications going so fast, the channel bandwidth limits the ability to transmit data.
PAM4 allows you to effectively double your data rate by doubling the amount of data per clock cycle.
5:05 What’s the downside of PAM4? The Signal to Noise Ratio (SNR) for PAM4 worse than traditional NRZ. In a perfect world, the ideal SNR would be 9.6 dB (for four levels instead of two). In reality, it’s worse, though.
5:30 Each eye may not be the same height, so that also has an effect on the total SNR.
6:05 What’s the bit error ratio (BER) of a PAM4 vs. NRZ signal if the transmission channel doesn’t change?
6:45 The channels were already challenged, even for many NRZ signals. So, it doesn’t look good for PAM4 signals. Something has to change.
7:00 PAM4 is designed to operate at a high BER. NRZ typically specified a 1E-12 or 1E-15 BER, but many PAM4 specs are targeting 1E-4 or 1E-5. It uses forward error correction (or other schemes) to get accurate data transmission.
7:50 Companies are designing more complex receivers and more robust computing power to make PAM4 work. This investment is worth it because they don’t have to significantly change their existing hardware.
8:45 PAM is being driven largely by Ethernet. The goal is to get to a 1 Tb/s data rate.
9:15 Currently 400 GbE is the next step towards the 1 Tbps Ethernet rate (terabit per second).
10:25 In Steve’s HP days, the salesmen would e-mail large pictures (1 MB) to him to try to fill up his drive.
11:10 Is there a diminishing rate of return for going to higher PAM levels?
PAM3 is used in automotive Ethernet, and 1000BASE-T uses PAM5.
Broadcom pushed the development of PAM3. The goal was to have just one pair of cables going through a vehicle instead of the 4 pairs in typical Ethernet cables.
Cars are an electrically noisy environment, so Ethernet is very popular for entertainment systems and less critical systems.
Essentially, Ethernet is replacing FlexRay. There was a technology battle for different automotive communication techniques. You wouldn’t want your ABS running on Ethernet because it’s not very robust.
For digital communications, PAM8 is not possible over today’s channels because of the noise.
15:20 PAM4 is the main new scheme for digital communications
15:50 Baseband digital data transmission covers a wide frequency range. It goes from DC (all zeroes or all ones) to a frequency of the baud rate over 2 (e.g. 101010). This causes intersymbol interference (ISI) jitter that has to be corrected for – which is why we use transmitter equalization and receiver equalization.
16:55 PAM4 also requires clock recovery, and it is much harder to recover a clock when you have multiple possible signal levels.
17:35 ISI is easier to think about on an NRZ signal. If a signal has ten 0s in a row, then transitions up to ten 1s in a row, the channel attenuation will be minimal. But, if you put a transition every bit, the attenuation will be much worse.
19:15 To reduce ISI, we use de-emphasis or pre-emphasis on the transmit side, and equalization on the receiver side. Engineers essentially boost the high frequencies at the expense of the low frequencies. It’s very similar to Dolby audio.
20:40 How do you boost only the high frequencies? There are circuits you can design that react based on the history of the bit stream. At potentially error-inducing transition bits, this circuitry drives a higher amplitude than a normal bit.
22:35 Clock recovery is a big challenge, especially for collapsed eyes. In oscilloscopes, there are special techniques to recover the eye and allow system analysis.
With different tools, you can profile an impulse response and detect whether you need to de-emphasize or modify the signal before transmission. Essentially, you can get the transfer function of your link.
23:45 For Ethernet systems, there are usually three equalization taps. Chip designers can modify the tap coefficients to tweak their systems and get the chip to operate properly. They have to design in enough compensation flexibility to make the communication system operate properly.
25:00 PAM vs. QAM? Is QAM just an RF and optical technique, or can it be used in a digital system?
25:40 Steve suspects QAM will start to be used for digital communications instead of just being used in coherent communication systems.
26:30 PAM4 is mostly applicable to the 200 GbE and 400 GbE, and something has to have to happen for us to get faster data transfer.
26:48 Many other technologies are starting to look into PAM4 – InfiniBand, Thunderbolt, and PCIe for example.
You can also read the EDN article on PAM4 here. If you’re working on PAM4, you can also check out how to prepare for PAM4 technology on this page.