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- TL;DR
- Why overclocking usually also needs to overvoltage?
When we overclock CPU or GPU or RAM we also have to increase the voltage to achieve stable operation (provided we have adequate cooling). Why is that?
Why do we need to increase voltage when overclocking PC components?
- Thread starter Delta2
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Discussion Overview
The discussion centers on the necessity of increasing voltage when overclocking CPU, GPU, or RAM components for stable operation. Participants explore the relationship between voltage, signal switching, and the implications for performance and reliability in electronic circuits.
Discussion Character
- Technical explanation
- Debate/contested
- Mathematical reasoning
Main Points Raised
- Some participants suggest that increasing voltage is necessary for stable operation during overclocking due to the time it takes for signals to reach their threshold voltage.
- One participant explains that higher applied voltage allows signals to change levels faster, akin to how a DC motor operates.
- Another participant raises a question about the limitations of clock speeds and the implications of running components at higher speeds without a clock.
- Some participants discuss the relationship between voltage, propagation delay, and power loss, noting that increasing voltage can decrease propagation delay but also significantly increase power consumption.
- There is mention of asynchronous logic gates that do not require a clock, which some argue is not relevant to traditional overclocking discussions.
- A participant emphasizes that while overclocking can yield performance gains, it also increases heat generation and potential reliability issues.
- Another participant proposes that a deeper understanding of propagation delay calculations could clarify the effects of voltage on switching speed.
Areas of Agreement / Disagreement
Participants express differing views on the relevance of certain topics, such as asynchronous CPUs and the implications of clock speeds. There is no consensus on the best approach to overclocking or the necessity of increasing voltage, as various models and explanations are presented.
Contextual Notes
Participants note that the relationship between voltage, propagation delay, and power consumption is complex, with dependencies on specific circuit designs and conditions. The discussion highlights the trade-offs involved in overclocking, including potential reliability issues due to increased heat and power loss.
- #2
Tom.G
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Because during switching, it takes time for the signals to reach their final voltage.
If you tell them to switch more often, they eventually don't reach their needed 'threshold voltage' before they are told to switch back again. The 'threshold voltage' is an internal design parameter in the chips and is the 'decision point' where the chip decides if the signal is High or Low. It is relatively stable over supply voltage.
Just like a DC motor, the higher the applied voltage, the faster the signals will change level; and the sooner the chips detect the level change.
That's the 'easy' version, the full version needs a lengthy study in physics, electronic design, and solid state physics.
Hope it helps!
Cheers,
Tom
If you tell them to switch more often, they eventually don't reach their needed 'threshold voltage' before they are told to switch back again. The 'threshold voltage' is an internal design parameter in the chips and is the 'decision point' where the chip decides if the signal is High or Low. It is relatively stable over supply voltage.
Just like a DC motor, the higher the applied voltage, the faster the signals will change level; and the sooner the chips detect the level change.
That's the 'easy' version, the full version needs a lengthy study in physics, electronic design, and solid state physics.
Hope it helps!
Cheers,
Tom
- #3
Keith_McClary
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A kid was shocked to learn that there was a clock to slow down our computer! Why not just let it run infinitely fast?
- #4
berkeman
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Was that kid you? Otherwise, how does your post help this thread?Keith_McClary said:
- #5
Keith_McClary
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It's another aspect of the same limitations of the electronics.berkeman said:
- #6
berkeman
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Wakarimasen. I don't understand.
Please explain your reply in detail with technical details and reference links. Thanks.Keith_McClary said:
- #7
Baluncore
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There is a class of logic gates that do not need a clock. They employ more than one conductor per bit, and different combinations of signals have either a valid or an invalid state.
The output becomes invalid when any input changes. Once the output combination becomes valid, it is correct. See; Asynchronous Logic.
https://en.wikipedia.org/wiki/Asynchronous_circuit#Asynchronous_CPU
The output becomes invalid when any input changes. Once the output combination becomes valid, it is correct. See; Asynchronous Logic.
https://en.wikipedia.org/wiki/Asynchronous_circuit#Asynchronous_CPU
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Sorry guys but I find posts #3 to #7 off topic. @Keith_McClary is probably trolling the overclocking community but I don't understand why @Baluncore decided to throw in the case of asynchronous CPU. OK no clock there so not possible overclocking at least not in the traditional sense.
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- #9
Keith_McClary
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The answer to both questions is that the circuit requires a certain minimum time (which may depend on voltage) to complete a cycle.berkeman said:
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How this minimum time to complete a cycle can depend on voltage?Keith_McClary said:
- #11
Keith_McClary
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As explained by Tom.GDelta2 said:
- #12
Baluncore
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You can run a CPU at the specified clock rate reliably. You may be able to run it faster, but at some speed, voltage, and temperature, it will become unreliable.Delta2 said:
CMOS logic swings between the supply rails.
1% higher supply voltage offers 1% higher gate voltages.
Gate voltage 1%, determines CMOS channel conductance 2%, (square law).
Gate outputs slew through 1% greater voltage, with 2% more conductance, so is only 1% faster.
But the 1% greater voltage and 2% greater conductance makes for 3% greater power.
So the overclocked chip only goes 1% faster, but it produces 3% more heat.
Thresholds drift with temperature. That is not a recipe for reliability.
You have no idea how often an overclocked CPU is doing a bad computation.
While the temperature and voltage may change, an asynchronous CPU always runs reliably at the maximum possible speed.Delta2 said:
You know that an asynchronous CPU is going as fast as is possible, and that it is not doing bad computations.
- #13
alan123hk
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Delta2 said:
I think that an in-depth study of the actual calculation formula of the propagation delay time of CMOS circuits will help us understand why increasing the power supply voltage can speed up the switching speed.
Please refer to the following link:
http://web.mit.edu/6.012/www/SP07-L13.pdf
Obviously, when the power supply voltage increases, according to the relevant equations, the propagation delay from high to low and the propagation delay from low to high will decrease respectively.
Unfortunately, the power loss will also greatly increase in proportion to the square of the power supply voltage.
- #14
Baluncore
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The power equation on page 13 shows that a 1% increase in Vdd increases power by 2%, (square), and the 1% increase in frequency makes it a 3% increase in power.alan123hk said:
- #15
alan123hk
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Baluncore said:
I totally agree with you.
That's it, because the power loss is proportional to the square of the power supply voltage, so 1.012 = 1.02, namely 1% to 2%.
If we assume the gate threshold voltage (Vtp) is much smaller than the supply voltage (Vdd), then the propagation delay reduction is approximately equal to 1.01/1.012 = 0.99, which means that 1% increase of voltage can increase 1% of speed or frequency accordingly, so the total power is increased by 1.02*1.01 = 1.03 (3%)
By the way, I think it is possible to estimate how much voltage we should increase under a certain level of overclocking according to the calculation formula of the propagation delay time.
