CFS0303-SB_08 Datasheet, PDF (14/17 Pages) Mimix Broadband – 0.1-10.0 GHz Low Noise, Medium Power

0.1-10.0 GHz Low Noise, Medium Power
pHEMT in a Surface Mount Plastic Package
May 2008 - Rev 02-May-08
CFS0303-SB
Considerations When Designing for Optimum
Noise Figure Using Noise Parameters
For any two-port network, the noise figure gives a
measure of the amount of noise added to a signal transmit-
ted through that network. In this data sheet we have given
the NFmin and the corresponding optimum source resis-
tance values for the device under various bias conditions.
NFmin represents the true minimum noise figure when the
device is presented with an impedance matching network
that transforms the source impedance typically 50 ohms to
that optimum noise matching impedance referred to as
Gopt. All stability considerations still apply, of course. If
the calculated Rollet stability factor (K) is less than 1, then
the source and load reflection coefficients must be carefully
chosen. For an accurate graphical depiction of the unstable
regions, it is best to draw stability circles.
In practice the impedance that minimizes the noise
figure is different from the impedance that minimizes the
return loss. Matching techniques such as inductive feedback
will be used to bring the noise match closer to this gain
match. An additional inherent danger of this technique is the
increased instability of the design at higher frequencies. As
the frequency increases the source inductance will also
increase, this increases the amount of feedback to the
devices source up to an oscillation level. This issue can be
reduced by carefully choosing the input and output match-
ing topology so that the transducer gain is limited at the fre-
quency of potential oscillation. Design of a high pass / low
pass matching network on the input and output is one solu-
tion that addresses this problem. Careful simulation is
essential using the wideband s-parameters provided and can
only be achieved through careful modeling of all compo-
nents utilized in the design, including:
1. Accurate high frequency models for all surface
mount components used.
2. Accurate models of the board characteristics
including loss tangents and metal thickness.
3. Use of Via holes and via pads instead of perfect
grounds where used.
In any case if the reflection coefficient of the cho-
sen matching network is other than Gopt, then the noise fig-
ure of the device will be greater than NFmin. The losses of
the matching circuits are also non-zero and it must be con-
sidered that the noise figure of the completed amplifier is
equal to the noise figure of the device plus the losses of the
matching network preceding the device.
The losses of the matching networks are related to
the Q of the components and associated printed circuit
board loss. In general larger gate width devices will typical-
ly have a lower Gopt as compared to smaller gate width
devices. Matching to higher impedance devices requires
very hi-Q components in order to minimize circuit losses.
The main reason for using smaller gate width devices is the
trade-off of current consumption and optimum noise perfor-
mance. The CFS0301 is a 600um gate width device has a
minimum noise figure of 0.18 dB and a Gopt of 45+j109,
making it significantly easier to match than competitive
devices. Associated gain Ga is 19.3dB.
Device Non-Linear Model
Mimix develops its own non-linear model based
on its own internal device characterization. The model is
verified in different simulators and compared to the original
data from which it was extracted.
Mimix Broadband, Inc., 10795 Rockley Rd., Houston, Texas 77099
Tel: [phone] Fax: [phone] mimixbroadband.com
Page 14 of 17
Characteristic Data and Specifications are subject to change without notice. ©2008 Mimix Broadband, Inc.
Export of this item may require appropriate export licensing from the U.S. Government. In purchasing these parts, U.S. Domestic customers accept
their obligation to be compliant with U.S. Export Laws.