Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Average Current , RMS current ?

Status
Not open for further replies.

tomph

Junior Member level 1
Joined
May 23, 2005
Messages
18
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,502
average current rms current

I 'm running fullchip simulation to extract the current consumption during operations using HSIM tool .
I 'm not sure which of the below type of currents I should watch
Average current , RMS current, Intergration current

Could anyone who is familiar w/ the tool can help to explain the different between
those kind of currents. i.e why RMS ....When we need RMS...

Thank you for your help.
Tomph
 

is average current equal to dc current?

In my opition, choose either current is Ok, because Aver and RMS current are nearly same. Choose Average for more precision, because power=V*Iavg.

The following is a power simulition result by hsim, which shows Avg~=RMS

Signal Name Average RMS Min Max
--------------------------------------------------------------------
/i1(vdd) -31.7mA 31.7mA -34.7mA -28.8mA
 

average current and rms

I think you may find answer in the spec. of your products.
Basically,for estimating the power consumption purpose, you'd better to use average current because the power consumption=Iavg*Vdd, in which Vdd is a constant voltage. You can also measure the peak current,which indicates the maxium pulse current that decides the generator capability and bypass capacitors value.
 

I think you could choose Average current. Because RMS current is Root Mean Square current.
 

Why average current??
In some cases those two currents are so different. For example, the current can be negitive sometime. Then the average current doesnt accurately represent the power consumption. So I think that RMS current may be the better one to calculate power consumption

Ablue
 

u can refer to

I think this should be useful
 

RMS : when the heat amount generated by current through a resistor

is equal to a DC current, we say that DC current is the current's

RMS value.

AVERAGE current is the averaged current.

best regards



tomph said:
I 'm running fullchip simulation to extract the current consumption during operations using HSIM tool .
I 'm not sure which of the below type of currents I should watch
Average current , RMS current, Intergration current

Could anyone who is familiar w/ the tool can help to explain the different between
those kind of currents. i.e why RMS ....When we need RMS...

Thank you for your help.
Tomph
 

By definition the power dissipation is the average value of the instantaneous power dissipation - v(t)*i(t), i.e,
Pav=lim 1/T ∫ v(t)i(t) dt as T->∞

in the usual case where v(t)=VDD this reduces to
Pav=VDD lim 1/T ∫ i(t) dt=VDD*Iav as T->∞

where Iav is the AVERAGE current.

People sometimes confuse this because of sinusoidal regime, were if
v(t)=Vm Cos(wt) and i(t)=Im Cos(wt),

we have
Pav=lim 1/T ∫ v(t)i(t) dt as T->∞ =

= 1/T ∫ v(t)i(t) dt (T is the period: w=2Pi/T)=
=VmIm/2= Vm/√2*Im/√2=Vrms*Irms
 

maxwellequ said:
By definition the power dissipation is the average value of the instantaneous power dissipation - v(t)*i(t), i.e,
Pav=lim 1/T ∫ v(t)i(t) dt as T->∞

in the usual case where v(t)=VDD this reduces to
Pav=VDD lim 1/T ∫ i(t) dt=VDD*Iav as T->∞

where Iav is the AVERAGE current.

People sometimes confuse this because of sinusoidal regime, were if
v(t)=Vm Cos(wt) and i(t)=Im Cos(wt),

we have
Pav=lim 1/T ∫ v(t)i(t) dt as T->∞ =

= 1/T ∫ v(t)i(t) dt (T is the period: w=2Pi/T)=
=VmIm/2= Vm/√2*Im/√2=Vrms*Irms


The definition is correct, i guess should use average,but what will happen if the current is positive for a while and nagative for a while?can we say that a resistor can supply power if a negative current is passing throught it?
 

Dear dog1357,

In a resistor you never have that situation.

Due to capaciive/inductive effects it may happen that the circuit is supplying current to the source - instantaneous power is negative.

However, the power dissipation is obtained by averaging the instantaneous power during a sufficiently large amount of time.

Rgds
 

In a full-chip simulation, you are more likely to have a positive current coming out of the supply 'on average', unless your full chip is a theoretical tank circuit. So average would do fine.

If the start up period is long, then clip that portion to get a more accurate estimate.

I would be more interested in finding out currents going to individual blocks, since they determine the size of the power traces eventually and the placement of blocks and pads. If one of the blocks has +ve and -ve current, you can always deal with it separately and if it is periodic, you can always find the rms current consumption for it. rms value would depend on the shape of the current waveform.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top