Download SPIRIT1: increasing the output power

AN4198
Application note
SPIRIT1: increasing the output power
By Giuseppe Cantone
Introduction
The SPIRIT1 is a very low-power RF transceiver, intended for RF wireless applications in
the sub-1 GHz band. It is designed to operate both in the license-free ISM and SRD
frequency bands at 169, 315, 433, 868 and 915 MHz.
This application note reports the modifications in the PCB schematic and in the SPIRIT1
configuration to increase the output power in transmission mode, the maximum output
power achievable and the related current consumption measurements in the ISM frequency
bands.
November 2012
Doc ID 023916 Rev 1
1/12
www.st.com
Contents
AN4198
Contents
1
Application circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2
Maximum output power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1
170 MHz band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2
315 MHz band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3
434 MHz band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4
868 MHz band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.5
920 MHz band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3
Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4
Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
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AN4198
1
Application circuit
Application circuit
The SPIRIT1 integrates a switched mode power supply (SMPS) regulator allowing operation
from a battery voltage ranging from +1.8 V to +3.6 V. With power conversion efficiency of at
least 80%, the SMPS saves current consumption in the active mode.
In the default configuration the transmitter power amplifier (PA) output (pin 12 of the
SPIRIT1) is biased by the 1.4V SMPS voltage output through the L0 external inductor
(Figure 1). This limits the maximum output power at about +11 dBm, measured at the 50
Ohm connector via the reference design.
Biasing the PA output through the inductor L0 directly connected to the battery, instead of
the SMPS output (as shown in Figure 2) allows the maximum output power delivered at the
50 ohm connector (or at the antenna) to be increased. The maximum output power changes
with the voltage level applied at the PA output. Section 2 reports the maximum output power
achievable changing the voltage level in each ISM sub-band.
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4
5
SCLK
CSn
CSn
SCLK
SDI
VBAT2
GPIO_2
XIN
GPIO_1
XOUT
8
XTAL
10
Doc ID 023916 Rev 1
15
11
12
13
14
L7
VCC_RF
L_10U_0805
SDn
C_TBD_0402_C0G
C19
C_10P_0402_C0G
C10
REXT
TX
SMPS2
SMPS1
SDn
21
C_12P_0402_C0G
6
Y1
RXP
NX3225GA-xxMHz (XTAL)
C20 C_1U_0603_X7R
C21 C_100p_0402_C0G
VCC_RF
RXN
C9
GPIO_3
GPIO_0
VREG
GND
SPIRIT1
3
SDI
20
VBAT1
SDO
19
2
18
1
17
GPIO0
16
SDO
U1
C0
C_100n_0402_X7R
L_TBD_0402
L1
L_TBD_0402
C4
L_TBD_0402
C_TBD_0402_C0G
C1
L2
C11
C_1U_0603_X7R
C_TBD_0402_C0G
L_TBD_0402
L4
C_TBD_0402_C0G
C5
C_TBD_0402_C0G
L_TBD_0402
L6
C6
L5
C_TBD_0402_C0G
C15
TX OUT
L0
L_TBD_0402
L_TBD_0402
L8
C14
C_TBD_0402_C0G
C7
C_TBD_0402_C0G
C2
C_TBD_0402_C0G
C8
C13
C_TBD_0402_X7R
C_TBD_0402_C0G
C3
C_TBD_0402_C0G
L3 L_TBD_0402
L_TBD_0402
L9
C12
C_100n_0402_X7R
Figure 1.
GPIO3
GPIO2
GPIO1
C_330p_0402_C0G
C22
Application circuit
AN4198
PA output biased by SMPS voltage
9
7
AM16920V1
4
5
SCLK
CSn
CSn
SCLK
SDI
XIN
GPIO_1
XOUT
8
6
Doc ID 023916 Rev 1
C9
VBAT2
SDn
REXT
TX
SMPS2
SMPS1
15
11
12
13
14
L7
VCC_RF
L_10U_0805
SDn
C_TBD_0402_C0G
C19
C_10P_0402_C0G
C10
10
C_12P_0402_C0G
GPIO_3
Y1
RXP
NX3225GA-xxMHz (XTAL)
C20 C_1U_0603_X7R
C21 C_100p_0402_C0G
VCC_RF
RXN
XTAL
GPIO_2
GPIO_0
VREG
GND
SPIRIT1
3
SDI
20
VBAT1
SDO
19
2
18
1
17
GPIO0
U1
16
SDO
GPIO3
GPIO2
GPIO1
C_330p_0402_C0G
C0
C_100n_0402_X7R
L_TBD_0402
L1
L_TBD_0402
C4
C_TBD_0402_C0G
C1
L_TBD_0402
L2
C11
C_1U_0603_X7R
C_TBD_0402_C0G
L_TBD_0402
L4
C_TBD_0402_C0G
C5
C_TBD_0402_C0G
L_TBD_0402
L6
C6
L5
C_TBD_0402_C0G
C15
TX OUT
L0
L_TBD_0402
VCC_RF
L_TBD_0402
L8
C14
C_TBD_0402_C0G
C7
C_TBD_0402_C0G
C2
C_TBD_0402_C0G
C8
C13
C_TBD_0402_X7R
C_TBD_0402_C0G
C3
C_TBD_0402_C0G
L3 L_TBD_0402
L_TBD_0402
L9
C12
C_100n_0402_X7R
J1
RF_IN/OUT
Figure 2.
21
C22
AN4198
Application circuit
PA output biased by battery voltage
9
7
AM16921V1
5/12
Maximum output power
2
AN4198
Maximum output power
All the measurements here reported are performed at room temperature. The output power
of the wanted emission, as well as the unwanted emission and the harmonics level, is
delivered at the 50 Ohm single-ended load via the reference design.
The voltage supply VBAT feeds the SPIRIT1, as well as the PA output (Figure 2).
The SPIRIT1 has been configured to emit the maximum value of output power, setting the
PA_LEVEL word of the SPIRIT1 PA_POWER registers with PA_LEVEL=1.
2.1
170 MHz band
Table 1.
170 MHz maximum output power and current consumption
Voltage supply
Maximum output power
Current consumption
VBAT
(measured at connector)
(TX mode)
3.6 V
+16.1 dBm
54 mA
3.0 V
+15.6 dBm
51 mA
2.4 V
+14.8 dBm
44 mA
1.8 V
+13.0 dBm
27 mA
Figure 3.
170 MHz maximum output power and current consumption chart
AM16922V1
6/12
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AN4198
2.2
Maximum output power
315 MHz band
Table 2.
315 MHz maximum output power and current consumption
Voltage supply
Maximum output power
Current consumption
VBAT
(measured at connector)
(TX mode)
3.6 V
+16.4 dBm
52 mA
3.0 V
+15.8 dBm
50 mA
2.4 V
+14.7 dBm
44 mA
1.8 V
+12.7 dBm
32 mA
Figure 4.
315 MHz maximum output power and current consumption chart
AM16923V1
2.3
434 MHz band
Table 3.
434 MHz maximum output power and current consumption
Voltage supply
Maximum output power
Current consumption
VBAT
(measured at connector)
(TX mode)
3.6 V
+16.5 dBm
49.3 mA
3.0 V
+16.2 dBm
49 mA
2.4 V
+15.9 dBm
48.8 mA
1.8 V
+14.6 dBm
46.6 mA
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Maximum output power
Figure 5.
AN4198
434 MHz maximum output power and current consumption chart
AM16924V1
2.4
868 MHz band
Table 4.
8/12
868 MHz maximum output power and current consumption
Voltage supply
Maximum output power
Current consumption
VBAT
(measured at connector)
(TX mode)
3.6 V
+15.5 dBm
44 mA
3.0 V
+15.1 dBm
44 mA
2.4 V
+14.9 dBm
43 mA
1.8 V
+14.0 dBm
35 mA
Doc ID 023916 Rev 1
AN4198
Maximum output power
Figure 6.
868 MHz maximum output power and current consumption chart
AM16925V1
2.5
920 MHz band
Table 5.
920 MHz maximum output power and current consumption
Voltage supply
Maximum output power
Current consumption
VBAT
(measured at connector)
(TX mode)
3.6 V
+16 dBm
45.2 mA
3.0 V
+15.7 dBm
44.9 mA
2.4 V
+15.2 dBm
44.5 mA
1.8 V
+14.1 dBm
44.5 mA
Doc ID 023916 Rev 1
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Reference
AN4198
Figure 7.
920 MHz maximum output power and current consumption chart
AM16926V1
3
Reference
[1] STMicroelectronics SPIRIT1 datasheet.
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AN4198
4
Revision history
Revision history
Table 6.
Document revision history
Date
Revision
22-Nov-2012
1
Changes
Initial release.
Doc ID 023916 Rev 1
11/12
AN4198
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