Speaker 1: All right, welcome back everyone. Today we're going to be
Speaker 1: looking at something super important in electronics design, minimizing and
Speaker 1: exploiting leakage in VLSI design. Oh yeah, you know, like,
Speaker 1: uh deal, have you ever noticed your phone battery like draining,
Speaker 1: even when it's just sitting.
Speaker 2: There, happens all the time.
Speaker 1: Turns out that's leakage power in action, and it's something
Speaker 1: that engineers designing chips have to deal with constantly.
Speaker 2: Oh yeah, absolutely, we're going to.
Speaker 1: Be taking a deep dive into all that today using
Speaker 1: this book by doctor Sunil Pikatre. Okay, he and a
Speaker 1: whole team of researchers really dove deep into the world
Speaker 1: of low power chip design. Yeah, they really know their stuff,
Speaker 1: So get ready to explore how those tiny chips use power,
Speaker 1: the clever tricks engineers use to you know, minimize energy waste,
Speaker 1: and even some ways that they've learned to actually use
Speaker 1: leakage to their advantage. It's pretty amazing, kind of counterintuitive,
Speaker 1: yeah for sure. So when we talk about power consumption
Speaker 1: in chips, you usually think of dynamic power, right, Yeah,
Speaker 1: that's the energy it chip uses when it's actively computing. Yeah, exactly,
Speaker 1: it's doing stuff uh huh. But there's this other thing,
Speaker 1: this leakage power that we don't always think about.
Speaker 2: Yeah, it's like a silent drain on the battery.
Speaker 1: Right, even when a transistor is supposed to be off,
Speaker 1: that's right, it's still leaking a bit of energy.
Speaker 2: Like a leaky faucet.
Speaker 1: Yeah, exactly.
Speaker 2: And you know what, this problem actually gets worse as
Speaker 2: transistors get smaller.
Speaker 1: Oh really, why is that?
Speaker 2: Well? Think of it like this. As we shrink those
Speaker 2: transistors down to pack more and more into our.
Speaker 1: Devices, right, trying to get more powerful chips.
Speaker 2: Exactly, the gaps between them get tinier and tinier. Okay,
Speaker 2: it's like trying to prevent water from seeping through cracks
Speaker 2: in a dam.
Speaker 1: Right, smaller the gaps, the harder it is.
Speaker 2: Exactly.
Speaker 1: So it's like the electrons are finding more ways to
Speaker 1: sneak through.
Speaker 2: You can think of it that way. Yeah, it's a
Speaker 2: quantum phenomenon.
Speaker 1: Actually quantum wow called tunneling.
Speaker 2: Electrons can actually tunnel through barriers that, according to classical physics,
Speaker 2: they shouldn't be able to cross, So they're like teleporting.
Speaker 2: It's kind of like that. The equation that describes all
Speaker 2: this can get pretty complex.
Speaker 1: Ill bet.
Speaker 2: But the important thing to remember is that the amount
Speaker 2: of leakage depends on something called the threshold voltage.
Speaker 1: Okay, the threshold voltage.
Speaker 2: And it's an exponential relationship.
Speaker 1: Exponential, So even a small change in that voltage, yeah,
Speaker 1: could mean a big difference in leakage, huge difference.
Speaker 2: That's why controlling that threshold voltage is so crucial for
Speaker 2: designing low power chips.
Speaker 1: Makes sense.
Speaker 2: Historically though, we've been focused on making chips faster and
Speaker 2: more powerful, right, which often meant lowering that threshold.
Speaker 1: Voltage, which then increases leakage unfortunately.
Speaker 2: Yes, so there's this constant tug of war between performance
Speaker 2: and power efficiency.
Speaker 1: So how do engineers tackle this leakage problem?
Speaker 2: It's a real challenge.
Speaker 1: Do they like build tiny walls to keep the electrons in?
Speaker 2: Uh huh? Not quite. But they do have some clever strategies, okay,
Speaker 2: like what Well, one common technique is called mtcms mtcmos.
Speaker 1: What's that stand for?
Speaker 2: Multi threshold cmos. It's basically like putting parts of the
Speaker 2: chip to sleep when they're not being used.
Speaker 1: Oh, like a power nap for the chip exactly.
Speaker 2: They use high threshold voltage transistors as gatekeepers to shut
Speaker 2: off power to inactive sections.
Speaker 1: So that drastically reduces leakage in those areas. It does,
Speaker 1: but I guess there's a trade off there, there is.
Speaker 1: Waking those sections back up takes little.
Speaker 2: Time, right, so it can slightly impact performance.
Speaker 1: Ah, so you lose a bit of responsiveness.
Speaker 2: Yeah, but you gain in power savings, gotcha.
Speaker 1: So it's always a.
Speaker 2: Balance, always a balance. Yeah.
Speaker 1: Makes you wonder if there are other ways to reduce
Speaker 1: leakage without sacrificing performance. Oh.
Speaker 2: Absolutely. Engineers have come up with all sorts of techniques
Speaker 2: like what well, things like designing special low leakage cells, okay,
Speaker 2: carefully controlling the input signals to the.
Speaker 1: Chip right to minimize the leakage.
Speaker 2: Exactly, and even adjusting the physical length of those tiny transistors.
Speaker 1: Wow, so they're really getting down to the nitty.
Speaker 2: Gritty they are. Each approach has its pros and cons.
Speaker 2: Of course, it really depends on the specific application and
Speaker 2: the design constraints.
Speaker 1: I can imagine. It's amazing how much effort goes into
Speaker 1: managing something as tiny as electron leakage.
Speaker 2: It's really quite impressive.
Speaker 1: I mean, it really shows how crucial power efficiency is
Speaker 1: in chip design.
Speaker 2: It really is, and you know, it makes you wonder,
Speaker 2: what's that? What if instead of just trying to minimize
Speaker 2: this leakage, we could actually use it to our advantage.
Speaker 1: Use it really Yeah, that's.
Speaker 2: The idea behind something called sub threshold circuit design.
Speaker 1: Sub threshold design, what's that all about?
Speaker 2: What's a pretty radical concept. Instead of trying to eliminate
Speaker 2: leakage by keeping those transistors firmly off right, sub threshold
Speaker 2: design actually operates the transistors below their threshold voltage.
Speaker 1: Below the threshold, so they're intentionally leaky exactly.
Speaker 2: It might sound crazy, but hear me out. It's a
Speaker 2: clever way to achieve all for low power consumption, especially
Speaker 2: when speed isn't the main concern.
Speaker 1: Okay, I'm intrigued, but why would you want to do that?
Speaker 1: I mean, isn't leakage a bad thing traditionally?
Speaker 2: Yes, But in the sub threshold region transistors have some
Speaker 2: unique characteristics. By operating them at these lower voltages, you
Speaker 2: can achieve dramatically lower power consumption.
Speaker 1: Interesting, so it's like whispering instead of shouting. You might
Speaker 1: not be as fast, but you save a lot of energy.
Speaker 2: That's a great analogy, and for things like low power
Speaker 2: sensors or medical implants where battery life is crucial. That
Speaker 2: energy saving can be a game changer.
Speaker 1: So are there real world examples of this sub threshold
Speaker 1: design in action.
Speaker 2: Absolutely? In fact, the book we're looking at today features
Speaker 2: a fascinating case study.
Speaker 1: Oh what is it?
Speaker 2: It's a sub threshold b FSK transmitter chip DFSK.
Speaker 1: What's that?
Speaker 2: It stands for a binary frequency shift keying. It's a
Speaker 2: method for a wireless communication And they designed this entire
Speaker 2: transmitter using sub threshold circuits. Wow, they were able to
Speaker 2: achieve significantly lower power consumption compared to traditional designs.
Speaker 1: That's impressive a wireless transmitter running on leaky transistors. But
Speaker 1: I'm guessing designing in the sub threshold region comes with
Speaker 1: its own set of challenges.
Speaker 2: You're absolutely right. Transistors in this leaky state are much
Speaker 2: more sensitive to variations variations like what things like temperature, voltage,
Speaker 2: even tiny manufacturing differences. Oh wow, it's like trying to
Speaker 2: build a house of cards on a shaky table. Yeah.
Speaker 1: I can see that you need some serious engineering magic
Speaker 1: to make that work reliably.
Speaker 2: Exactly, And that's what makes these designs so ingenious. They
Speaker 2: have to come up with clever tricks to keep everything stable.
Speaker 1: So what kind of tricks are we talking about.
Speaker 2: Well, one of their secret weapons is something called plaslas
Speaker 2: programmable logic arrays. They're like reconfigurable building blocks in the
Speaker 2: digital part of the circuit. Okay, they could be programmed
Speaker 2: to perform specific.
Speaker 1: Functions, so they're like logic legos. You can rearrange them
Speaker 1: to create different circuits.
Speaker 2: That's a great way to think about it. And what
Speaker 2: makes plas particularly useful in sub threshold design is their
Speaker 2: predictable structure.
Speaker 1: Right, so even though the transistors are leaky, the overall
Speaker 1: behavior is still controlled precisely.
Speaker 2: Now. On top of that, they use something called adaptive
Speaker 2: body biasing to deal with those pesky variations.
Speaker 1: We talked about adaptive body biasing. That sounds pretty high tech.
Speaker 2: What does it do exactly, Well, it's basically a feedback mechanism.
Speaker 1: Feedback.
Speaker 2: Yeah. It constantly adjusts the voltage applied to the transistor's substrate.
Speaker 2: The substrate it's also called the body of the transistor.
Speaker 1: Oh okay, And.
Speaker 2: By adjusting that voltage, they can compensate for variations in temperature, voltage,
Speaker 2: and manufacturing.
Speaker 1: So it's like a self tuning system that keeps everything
Speaker 1: running smoothly.
Speaker 2: Exactly. It's pretty ingenious, right it is.
Speaker 1: This is all fascinating stuff. I'm really starting to see
Speaker 1: how this sub threshold design could be a game changer
Speaker 1: in electronics.
Speaker 2: It really is a new frontier.
Speaker 1: It makes you wonder, though, what other applications could benefit
Speaker 1: from these techechniques for minimizing and even exploiting leakage.
Speaker 2: Well, that's a great question. We've talked about the BFSK transmitter,
Speaker 2: but there's so many other possibilities. For example, have you
Speaker 2: considered medical implants.
Speaker 1: Oh yeah, like pacemakers or insulin pumps. Extending the battery
Speaker 1: life of those could be huge.
Speaker 2: Exactly, it could be life changing. People wouldn't need risky
Speaker 2: surgeries just to replace batteries, that's right.
Speaker 1: And what about wearable sensors. Those are getting more and
Speaker 1: more popular these days.
Speaker 2: Absolutely, imagine a smart watch or fitness tracker that never
Speaker 2: needs charging.
Speaker 1: Yeah, that would be amazing. No more worrying about my
Speaker 1: watch dying in the middle.
Speaker 2: Level workout, right, And it's not just consumer devices either.
Speaker 2: Remember we talked about data centers.
Speaker 1: Oh yeah, those are massive energy hogs they are.
Speaker 2: And as our reliance on cloud computing grows, their energy
Speaker 2: consumption is only going to.
Speaker 1: Increase, so sub threshold design could be a key part
Speaker 1: of making them more efficient.
Speaker 2: Absolutely, we could reduce their environmental impact and their operating
Speaker 2: costs significantly.
Speaker 1: It's incredible to think that something as tiny as a
Speaker 1: leaky transistor could have such a big impact on a
Speaker 1: global scale.
Speaker 2: It really highlights the importance of innovation in this field.
Speaker 1: This whole deep dive has been a real eye opener
Speaker 1: for me. We've gone from this seemingly annoying problem of
Speaker 1: leakage power to exploring cutting edge techniques that are pushing
Speaker 1: the boundaries of energy efficiency.
Speaker 2: It's a great example of how challenging conventional thinking can
Speaker 2: lead to some truly groundbreaking solutions.
Speaker 1: It makes you wonder what other hidden opportunities might be
Speaker 1: lurking out there in the world of electronics, just waiting
Speaker 1: to be discovered.
Speaker 2: There are definitely more secrets to uncover.
Speaker 1: Well. If this episode has sparked your curiosity about chips
Speaker 1: and circuits, I encourage you to dive deeper.
Speaker 2: Absolutely. Doctor Cottrey's book is a fantastic resource if you
Speaker 2: want to explore the technical details in.
Speaker 1: More depth, definitely check it out and Remember, the pursuit
Speaker 1: of energy efficiency is about more than just extending battery life.
Speaker 2: It's about building a more sustainable future for electronics and
Speaker 2: reducing our impact on the planet.
Speaker 1: That's a great point. So until our next deep dive,
Speaker 1: keep those minds curious and those questions flowing. There's always
Speaker 1: more to learn, always.
Speaker 2: Yeah. So plas they're like, Okay, you can think of
Speaker 2: them like a grid, and you connect input signals to
Speaker 2: output signals through through a network of transistors, okay, and
Speaker 2: by choosing which connections you make, you basically program the PLA.
Speaker 1: Oh so it's programmable, yeah, okay, and.
Speaker 2: It can do all sorts of different logic functions.
Speaker 1: It's kind of like a like a logic lego set, right,
Speaker 1: you just rearrange the pieces exactly.
Speaker 2: That's a really good way to put it. And what
Speaker 2: makes plas really well suited for it for the sub
Speaker 2: threshold design is because they're so structured. Okay, they're predictable, right.
Speaker 1: So even though the transistors are kind of doing their
Speaker 1: own thing, they're leaky leaky, Yeah, but the PLA as
Speaker 1: a whole is still like behaving the way it's supposed to.
Speaker 2: Exactly. You need that predictability in sub threscial design makes sense.
Speaker 1: So what about that adaptive body biasing?
Speaker 2: Oh right, yeah, you said it.
Speaker 1: Was like a feedback mechanism.
Speaker 2: It is.
Speaker 1: Does it like have tiny sensors that measure the temperature
Speaker 1: and voltage?
Speaker 2: Well, not exactly sensors in the traditional sense, okay, but
Speaker 2: it's it's really quite clever. How it works.
Speaker 1: How does it work? Then?
Speaker 2: So basically, there's a special reference.
Speaker 1: PLA reference PLA, Yeah.
Speaker 2: It's like a representative for all the other plas in
Speaker 2: the circuit, okay, And its delay is constantly being.
Speaker 1: Measured measured against what a reference clock signal, A clock signal, okay.
Speaker 2: And if the delay starts to drift, uh huh, it
Speaker 2: means something's off.
Speaker 1: So it's like a canary in a coal miner.
Speaker 2: Yeah, exactly. And there's this thing called a phase detector
Speaker 2: phase detector which compares the delay of that reference PLA
Speaker 2: to the clock signal.
Speaker 1: Hm.
Speaker 2: And if there's a mismatch, yeah, it triggers another circuit called.
Speaker 1: A charge pump a charge pump, yeah.
Speaker 2: And the charge pump either adds or removes charge from
Speaker 2: from the substrate. Of the transition from the substrate, which
Speaker 2: is also called the body of the transistort. Oh okay,
Speaker 2: and that adjustment to the charge actually tweaks the threshold voltage, so.
Speaker 1: They're fine tuning that voltage exactly.
Speaker 2: So even with all those variations in temperature and voltage
Speaker 2: and manufacturing, right, they can keep the circuit running smoothly.
Speaker 1: That's wild. So it's like a self tuning system, it is. Yeah,
Speaker 1: that's incredible, it really is. It makes you appreciate the
Speaker 1: ingenuity of these engineers. You know, they're working at such
Speaker 1: a tiny scale, it's amazing, but they're able to create
Speaker 1: these really complex systems.
Speaker 2: Yeah, and they work.
Speaker 1: They work, that's the amazing part. So we've talked about
Speaker 1: the BFSK transmitter, but what other applications could benefit from
Speaker 1: these techniques.
Speaker 2: Well, let's think about it. What about something like medical implants.
Speaker 2: Oh yeah, medical implants, those are a great example.
Speaker 1: Yeah, things like pacemakers and insulin pumps.
Speaker 2: Right exactly. Yeah, imagine if you could extend the battery
Speaker 2: life of those it would be huge huj Yeah, people
Speaker 2: wouldn't have to go through those risky surgery so often
Speaker 2: just to replace batteries.
Speaker 1: Yeah, that's a really good point. And then there's all
Speaker 1: those wearable sensors that are becoming so.
Speaker 2: Popular, right, fitness trackers, smart watches.
Speaker 1: Imagine if those never needed charging.
Speaker 2: Oh that would be amazing.
Speaker 1: I would never have to take mine on. It would
Speaker 1: be so convenient, and wouldn't it be great for you know,
Speaker 1: like medical applications too.
Speaker 2: Absolutely constant monitoring without worrying about the battery dying.
Speaker 1: Yeah, that's a great point. And it's not just limited
Speaker 1: to those small devices either.
Speaker 2: Right.
Speaker 1: Remember we talked about data centers.
Speaker 2: Oh yeah, those things use a ton of energy and.
Speaker 1: It's only going to get worse as we rely more
Speaker 1: and more on cloud computing.
Speaker 2: Definitely, sub threshold design could be a key part of
Speaker 2: making them more energy efficient.
Speaker 1: Yeah, imagine the impact on the environment and they're operating costs.
Speaker 1: It's incredible to think about. It is all because of
Speaker 1: these tiny, leaky transistors.
Speaker 2: It just goes to show that sometimes the biggest solutions
Speaker 2: come from thinking outside the box.
Speaker 1: Yeah, leakage was always seen as a problem to be solved, right,
Speaker 1: but now we're learning to harness.
Speaker 2: It and use it to our advantage.
Speaker 1: This whole deep dive has been amazing me too. We've
Speaker 1: gone from understanding this annoying problem to exploring these incredible
Speaker 1: techniques that are changing how we think about energy.
Speaker 2: Efficiency is really exciting stuff.
Speaker 1: It makes you wonder what other possibilities are out there
Speaker 1: just waiting to be discovered.
Speaker 2: I think there's a lot more to come.
Speaker 1: Can't wait to see what the future holds. While that
Speaker 1: about wraps up our deep dive into minimizing and exploiting
Speaker 1: leakage in VLSI design, thanks for having me. It was
Speaker 1: great having you on. If you want to learn more
Speaker 1: about this fascinating topic, I definitely recommend checking out doctor
Speaker 1: Kotree's book.
Speaker 2: Yeah, it's a great resource.
Speaker 1: It's full of insights and technical details. And remember, this
Speaker 1: pursuit of energy efficiency is about more than just making
Speaker 1: our batteries last longer. It's about creating a more sustainable
Speaker 1: future for electronics alutely and minimizing our impact on the planet.
Speaker 2: Couldn't have said it better myself.
Speaker 1: So until our next deep dive, keep those minds curious,
Speaker 1: keep asking questions, and keep learning. See next time.