# De Q'ing resistor purpose

#### vikramc98406

##### Full Member level 1
Hi ,

Can any one help understand the purpose of De Q'ing resistor?
any links related to these are helpful.

vikram

#### stenzer

##### Full Member level 4
Hi,

if you are talking about decreasing the Q factor of an RLC circuit, the resistor is used to dissipate power, thus reducing the Q factor. Q is defined as

Q = 2 • π • (Energy stored / Energy dissipated per cycle).

By introducing a De Q'ing resistor, this resistor dissipates energy.

For a practical RLC parallel circuit Q is given by [1, page 26]

Q_par = 1/R • sqrt(L/C)

and for a series RLC by

Q_ser = ω_0 • L/R = ω_0 • 1/(R • C).

As you can see, the series resistor (in both circuits) leads to a decrase of Q.

[1] http://tiij.org/issues/issues/winter2010/files/TIIJ%20fall-winter%202010-PDW2.pdf

greets

Last edited:

#### FvM

##### Super Moderator
Staff member
As the question is posted in PCB Layout rather than RF or Analog Design section, I fear it's really unclear what "De Q'ing" resistor means for you. Please give a typical example.

#### vikramc98406

##### Full Member level 1
Thanks Stenzer.

I think i have some starting point to understand this.

Thanks
Vikram