SKY65048-360LF Datasheet, PDF (2/19 Pages) Skyworks Solutions Inc. – 0.7-1.2 GHz Low Noise Amplifier

DATA SHEET • SKY65048-360LF LOW NOISE AMPLIFIER
Table 1. SKY65048-360LF Signal Descriptions
Pin #
Name
Description
1
BIAS1
Source lead for 1^st stage transistor
2
RFIN
3
N/C
RF input
No connection
4
VDD1
1^st stage DC power supply
Pin #
5
Name
FEEDBACK
6
N/C
7
RFOUT/VDD2
8
BIAS2
Description
Connect to RFOUT/VDD2 to reduce gain of
2^nd stage transistor
No connection
RF output. Requires a DC bias using an RF
choke inductor.
Source lead for 2^nd stage transistor
Functional Description
The SKY65048-360LF is a two stage, low noise amplifier with an
integrated interstage matching network and source inductors. The
device has a tested low NF of 0.65 dB and gain of 16.5 dB with
the recommended matching circuit. The device allows designers
to adjust current and gain without degrading the NF.
The external matching network largely dictates the RF
performance of the device. The matching network is required for
operation and special care should be taken when designing a
circuit board layout for the SKY65048-360LF. There are four
separate groups of external components: input, output, biasing,
and feedback.
Biasing
To properly bias a depletion mode pHEMT, both the gate and
drain of the device must be biased properly. At VGS = 0 V and
VDS > 2 V, the amplifier stage is in its saturated state and draws
the maximum amount of current, IDSS. A VDS of 5 V is
recommended to ensure proper performance.
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 remains unchanged at the operating frequency.
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 simplifies the design by
eliminating the need for a second DC supply. Values for resistor
components R1 and R2 can be changed to easily increase or
decrease the bias current to a desired level.
The first stage is biased at 20 percent of IDSS to achieve the best
NF performance. The gain and current of the 2^nd stage amplifier
can be adjusted without degrading the overall NF. More current in
the 2^nd stage yields better IP3 performance.
Biasing components R1, R2, C1, and C2 should be placed as
close to the package pins as possible. See Figure 30 for the
recommended board layout.
Source Inductance
The source inductance required on pins 1 and 8 (BIAS1 and BIAS2
signals, respectively) has been integrated on the die. This
simplifies board layout and reduces build variations.
Input and Output RF Matching Network
The input band-pass matching network consists of four
components. Component C1 serves as the input DC blocking
capacitor, C2 provides high frequency stability and improved input
return loss, and L1 and L2 are responsible for the best noise
match looking into the gate of the first stage amplifier.
Excess board trace should be eliminated at the input of the device
to minimize board losses. High-Q components should be used to
achieve the best NF of the amplifier. Murata GJM series
capacitors and Coilcraft HP or CS series inductors are
recommended. Any excess board or component loss on the input
of the device directly adds to the total measured NF.
The output matching network is band-pass network optimized for
output return loss.
The SKY65048-360LF Evaluation Board assembly diagram is
shown in Figure 31 and a circuit schematic is provided in
Figure 32.
Feedback
Feedback is implemented in the recommended circuit on the 2^nd
stage transistor. Feedback improves the input and output return
loss and high frequency stability. The gain of the device can be
increased by increasing the value of R3, which reduces the
amount of feedback present (gain for multiple feedback resistor
values is shown in Figure 30).
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
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November 12, 2009 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 201101D