SKY65053-377LF Datasheet, PDF (2/12 Pages) Skyworks Solutions Inc. – 0.45-6.0 GHz Low Noise Transistor

DATA SHEET • SKY65053-377LF LOW NOISE TRANSISTOR
Table 1. SKY65053-377LF Signal Descriptions
Pin #
Name
Description
1
DRAIN
RF output. Supply voltage required through
external RF choke.
2
SOURCE
Source lead. Provides DC self-biasing point
and AC ground.
Pin #
Name
3
GATE
4
SOURCE
RF input
Description
Source lead. Provides DC self-biasing point
and AC ground.
Functional Description
The SKY65053-377LF is a depletion mode pHEMT designed for
low noise, high frequency applications that demand high linearity.
The SKY65053-377LF has a typical NF of 0.8 dB tested at the
2.4 GHz wireless LAN frequency band. A gain of 16.5 dB typical is
achieved using the same circuit. The SKY65053-377LF can be
used for any application from 450 MHz up to 6 GHz.
Biasing
To properly bias a depletion mode pHEMT, both the gate and
drain of the device must be properly biased. At VGS = 0 V and VDS
≥ 2V, the device is in its saturated state and draws the maximum
amount of current, IDSS. Typically, the device achieves the best
balance of noise and linearity performance at VDS = 5V and
IDS = 55 mA. To control IDS, VGS must be biased with a negative
voltage supply.
To eliminate the need for a negative DC supply, self-biasing
should be used when a resistor is placed between one of the
source leads and ground. A bypass capacitor should be placed in
parallel to this resistor to provide an RF ground and to ensure
performance at the operating frequency remains unchanged.
When current flows from drain to source and through the resistor,
the source voltage becomes biased above DC ground. The gate
pin of the device should be left unbiased at 0 V, which creates the
desired negative VGS value. This greatly simplifies the design by
eliminating the need for a second DC supply.
RF Matching Networks
The circuit schematic (see Figure 12) shows the recommended RF
matching network used for the 2.4 GHz wireless LAN frequency
band. Components C1, C2, L1, and L2 provide the necessary
impedance match for NF and input return loss. Circuit board and
input matching structure losses on the input of the amplifier add
directly to the overall NF of the amplifier. It is critical to minimize
RF trace lengths and to use high-Q components to achieve
optimal NF performance.
Components R1 and C10 provide self-bias for the device and RF
grounding for one of the two source leads. Component C6 is
placed on the opposing source lead and is used to tune the
transistor’s internal source inductance.
The effect of source inductance varies with frequency. Too little
source inductance increases gain and high frequency stability, but
at the cost of decreased in-band stability. Too much source
inductance decreases high frequency stability and gain, but
increases in-band stability. It is very important to find the
optimum tuning of source inductance that balances all of these
variables.
The output matching topology is typical for an RF amplifier.
Component L4 is the RF choke that prevents RF signals from
reaching the DC supply. Component C11 is the output DC
blocking capacitor. Components C12 and L6 provide the best
impedance match for best linearity performance.
Electrical and Mechanical Specifications
The absolute maximum ratings of the SKY65053-377LF are
provided in Table 2. The recommended operating conditions are
specified in Table 3 and electrical specifications are provided in
Table 4.
Performance characteristics for the SKY65053-377LF are
illustrated in Figures 3 through 10.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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July 7, 2009 • Skyworks Proprietary and Confidential information • Products and Product Information are Subject to Change Without Notice • 201089C