Transcript
APPLICATION NOTE
SKY12212-478LF: Low Frequency Tuning Introduction
Abstract
The SKY12212-478LF is a high power handling, Single-Pole, Double-Throw (SPDT) silicon PIN diode switch. The device operates over the 50 MHz to 2.7 GHz band. It features low insertion loss, excellent power handling, and superb linearity with low DC power consumption. The SKY12212-478LF is well-suited for use as a high power transmit/receive switch in a variety of telecommunication systems such as Sat-Com, Cable TV, WiMAX, TD-SCDMA, or LTE base stations. The device is provided in a 4 x 4 mm, 16-pin Quad Flat No-Lead (QFN) package. The SKY12212-478LF block diagram is shown in Figure 1.
The operating range specified in the standard data sheet for the SKY12212-478LF is 50 MHz to 2.7 GHz. The part has the capability to operate at lower frequencies with high input power. With modifications to the external bias circuitry, the SKY12212478LF can operate from 20 MHz to 2700 MHz with low insertion loss, high isolation and 100 W power handling capability.
ANT
TX
RX
RX_BIAS
Theory of Operation Operating at frequencies below 200 MHz presents problems not seen at higher frequencies. The series transmit diode has a characteristic to self-rectify at low RF frequencies and high power levels. In the transmit mode, high harmonic content is observed at input power levels above 42 dBm. This requires an innovative solution to reduce harmonic levels and maintain low TX insertion loss and high RX isolation up to 100 Watts. The solution is to create an innovative bias decoupling network that reduces the harmonic distortion at low frequencies and high power levels.
Exposed Paddle S2403
Figure 1. SKY12212-478LF Block Diagram
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At high power levels, a high harmonic content occurs because the RF input frequency is close to the SRF of the RF choke/ DC bias inductors. As a result, the switch goes into an early compression state at power levels > 42 dBm. The bias inductors provide the RF choking on the DC bias lines without degrading the input and output VSWR. The inductor value must be selected properly as it affects the RF match. The solution is to modify the bias network by adding an additional inductor that has an SRF above the RF input. The inductors are positioned in series to each other with the highest value inductor placed next to the switch. This provides the highest RF reactance for the best RF blocking and best match at lower operating frequencies. The evaluation board schematic diagram for the SKY12212-478LF for low frequency operation is shown in Figure 2. The low frequency tuned evaluation board is shown in Figure 3. The bill of materials is shown in Table 1.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 •
[email protected] • www.skyworksinc.com 203126A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • February 14, 2014
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APPLICATION NOTE • SKY12212-478LF: LOW FREQUENCY TUNING
Antenna Port Bias Input
R1 33 Ω C13 1 μF
C12 10000 pF
C10 10000 pF
Transmitter Input Port
L9 1800 nH
L7 390 nH
L10 390 nH
N/C 16
15
14
C11 10000 pF
13
Transmitter Port Bias Input
L8 1800 nH 12 N/C
1
Antenna Port
L4 390 nH
Receiver Port Bias Input
L3 1800 nH
Exposed paddle connected to ground
10 N/C
3
L6 820 nH
R2 560 Ω
RX Bias
9
N/C 4 U1 SKY12212
5
C7 10000 pF
Receiver Output Port
11 N/C
2
C1 10000 pF
C9 10000 pF 6
7
8
R3 560 Ω
N/C
C2 10000 pF
Notes: Y0669
R1 value set for 5 V, 100 mA bias R2 and R3 values set for 28 V, 100 mA bias
Figure 2. SKY12212-478LF Evaluation Board Schematic for Low Frequency Tuning Diagram
Y0667
Figure 3. SKY12212-478LF Evaluation Board Layout for Low Frequency Tuning
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 •
[email protected] • www.skyworksinc.com 2
February 14, 2014 • Skyworks Proprietary lnformation • Products and Product Information are Subject to Change Without Notice • 203126A
APPLICATION NOTE • SKY12212-478LF: LOW FREQUENCY TUNING
Table 1. SKY12212-478LF Evaluation Board Bill of Materials Component
Value
Units
Size
Manufacturer
Mfr Part Number
Characteristics
C1, C2, C7, C9, C10, C11, C12
10000
pF
0603
Murata
GRM188R7H103K
X7R, 50 V, ±5%
C13
1
F
0603
Murata
GRM188R71C105K
X7R, 16 V, ±10%
L3, L8, L9
1800
nH
0805
Coil Craft
0805LS-182XJLB
±5%, SRF 246 MHz
L4, L7, L10
390
nH
0805
TOKO
LL2012-FR39K
±10%, SRF 330 MHz
L6
820
nH
0603
Coil Craft
00603LS-821XJLB
±5%, SRF 410 MHz
R1
33
1206
Panasonic
ERJ8ENF33R0V
250 mW, 1%
R2, R3
560
2512
Multicomp
MCPWR12FTEA5600
1.5 W, 1%
4 x 4 x 1.5 mm
Skyworks
SKY12212-478LF
Skyworks
EN33-D785-001
U1 EVB
Typical Performance Characteristics
0.0
0
–0.4
–5
–0.8
–10
–1.2 –1.6 –2.0
–15 –20 –25 ANT Return Loss (S11) with ANT to RX in Insertion Loss State RX Return Loss (S22) with ANT to RX in Insertion Loss State TX Return Loss (S33) with ANT to TX in Insertion Loss State ANT Return Loss (S11) with ANT to TX in Insertion Loss State RX Return Loss (S22) with ANT to TX in Insertion Loss State TX Return Loss (S33) with ANT to RX in Insertion Loss State
–30 –2.4 S31: ANT to TX in Insertion Loss State
0.4
0.8
1.2
1.6
2.0
2.4
Y0670
–3.0 0.0
–35
S21: ANT to RX in Insertion Loss State
–2.8
–40 0.0
2.6
0.4
0.8
1.6
2.0
2.4
2.6
Frequency (GHz)
Frequency (GHz)
Figure 5. Return Loss vs Frequency
Figure 4. Insertion Loss vs Frequency
0
0
–0.2
Insertion Loss (dB)
–10
–20
–30
–40
–0.4
–0.6 30 MHz 50 MHz 100 MHz 300 MHz 700 MHz 1000 MHz
–0.8
Y0673
–1.0
–50 S21: ANT to RX Isolation with ANT to TX in Insertion Loss State S31: ANT to TX Isolation with ANT to RX in Insertion Loss State
–60 0.0
0.4
0.8
1.2
1.6
2.0
Frequency (GHz)
Figure 6. Isolation vs Frequency
2.4
2.6
Y0672
Isolation (dB)
1.2
Y0671
Return Loss (dB)
Insertioin Loss (dB)
(TOP = +25°C, PIN = 0 dBm, ANT_DC = 5 V, TX_DC, RX_BIAS and RX_DC= 0/28 V, Characteristic Impedance [ZO] = 50 Ω, Unless Otherwise Noted)
–1.2 30
35
40
45
50
55
Power In (dBm)
Figure 7. Insertion Loss vs CW Input Power vs Frequency
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 •
[email protected] • www.skyworksinc.com 203126A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • February 14, 2014
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APPLICATION NOTE • SKY12212-478LF: LOW FREQUENCY TUNING
Summary Operating high power PIN diode switches at frequencies below 200 MHz presents problems not seen at higher frequencies. In the transmit mode, high harmonic content is observed at input
power levels above 42 dBm. The solution is to create an innovative bias decoupling network with two series RF chokes to reduce the harmonic distortion observed at low frequencies and high power levels.
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Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 •
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February 14, 2014 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • 203126A
