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Quescent current - RF Cafe Forums

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Guest
Post subject: Quescent current Posted: Sat Sep 24, 2005 12:23 pm
I wanna ask a basic question thats bothering me. In many of the ICs datasheet only the Quiescent current is given.If i have to decide that what current that IC will draw from battery then should i take into account only the quiescent current or something else as well ?


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IR
Post subject: Posted: Sun Sep 25, 2005 4:22 am

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
The quiescent current is ususally the current that the IC draws under no operation. Usually it is the lowest current. Once the device is doing some activity (Logic activity, amplification etc) the current consumption grows.
When you design a battery-operated device you should check the quiescent current consumption when the device is not being operated i.e. at STBY mode and it should be as low as possible to prolong the battey's life. Usually battery-operated devices are more in STBY mode than in operation mode so the quiescent current consumption is the more dominant in terms of battery's life.

_________________
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- IR


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danyku
Post subject: helloPosted: Sun Sep 25, 2005 11:03 am

Lieutenant

Joined: Sat Sep 24, 2005 5:34 am
Posts: 2
hello IR , its very nice to see somebody from home .
today i discovered this site .
i am a FR engineer to .
where do you work ?


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Guest
Post subject: Posted: Sun Sep 25, 2005 1:46 pm
Well, thanks for the answer IR. So it does mean that only the Quescent current is important is important when choosing a battery for MMIC, am i right ?


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IR
Post subject: Posted: Mon Sep 26, 2005 2:29 am

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
If you design a RF battery-operated circuit, then you should choose MMICs with low current consumption. The current won't change much when the MMIC is with or without input signal (It will change I assume by not more that 10% max. per device). The best thing for RF battery- operated devices is to do a discrete design (Discrete transistors as amplifiers or Mixers), or to choose amplifiers with a shut-down option- when the device is in shut-down it draws the quiescent current.

Good luck!

_________________
Best regards,

- IR


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Guest
Post subject: Posted: Wed Sep 28, 2005 9:07 am
Not neccesarily true. Amplifiers operating in saturation can operate much higher than the quiescent current easpecially if it is a class A/B or C amp. You must take this in account when selecting a battery or you may be dissapointed when you fall short on output power.


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IR
Post subject: Posted: Thu Sep 29, 2005 7:52 am

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
The guest from the previous post just forgot to mention that you pay in linearity when you operate in Class A-B or C and your output signal will be distorted (Depends on the class). So as we all know, efficiency and linearity operate against each other. You as a designer has to make the right trade-off between these 2 requirements[/u]

_________________
Best regards,

- IR


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Guest
Post subject: Posted: Thu Sep 29, 2005 9:04 am
You are correct it most certainly depends on the linearity requirements. Just wanted to make sure he new the penalty in case he plans to operate the amp near compression.



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