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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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SUMMARY
Increasing voltage is essential when overclocking CPU, GPU, or RAM to maintain stable operation. This is due to the need for signals to reach their 'threshold voltage' quickly enough during switching cycles. A higher applied voltage accelerates signal transitions, allowing chips to detect level changes more efficiently. However, this increase in voltage also leads to higher power consumption and heat generation, which can compromise reliability.
PREREQUISITES- Understanding of CMOS logic and its operation
- Knowledge of voltage and power relationships in electronic circuits
- Familiarity with overclocking principles and thermal management
- Basic concepts of propagation delay in digital circuits
- Study the propagation delay time calculations for CMOS circuits
- Explore the relationship between supply voltage and power consumption
- Learn about thermal management techniques for overclocked components
- Investigate the design and operation of asynchronous logic circuits
This discussion is beneficial for hardware enthusiasts, overclockers, electrical engineers, and anyone interested in optimizing the performance and reliability of PC components.
- #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:
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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:
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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.
