AN4111
Application note
BAL-NRF01D3 matched balun with integrated harmonics filter for
Nordic Semiconductor ultralow power transceivers
Introduction
The nRF24LE1, nRF24AP2, nRF51422 and nRF51822 QFN from Nordic Semiconductor
are 2.45 GHz combo chips with an ultralow power transceiver.
The BAL-NRF01D3 from STMicroelectronics is an ultra miniature balun for which the
matching impedance has been customized for the nRF24LE1 QFN-32, nRF24AP2-1CH,
nRF24AP2-8CH, nRF51422-QFAA, and nRF51822-QFAA Nordic Semiconductor circuits.
The BAL-NRF01D3 integrates matching network and harmonics filters. It uses
STMicroelectronics’ IPD technology on non-conductive glass substrate which optimizes RF
performance.
Compared to traditional discrete solutions (Figure
3),
STMicroelectronics BAL-NRF01D3
decreases the BOM count by 80%, from 5 components to 1 component (Figure
4).
This
results in a lower system cost solution.
The BAL-NRF01D3 has been tested and approved by Nordic Semiconductor in the
nRF2723 nRFgo module (from the nRFgo nRF24LE1 QFN-32 pins development kit) and the
nRF2752 nRFgo module (from the nRFgo nRF51x22 Developer Preview kit). The
BAL-NRF01D3 demonstrates a higher system performance compared to traditional
solutions. This document presents the test and performance results.
June 2013
DocID023194 Rev4
1/17
www.st.com
BAL-NRF01D3 preview
AN4111
1
1.1
BAL-NRF01D3 preview
Features
50
nominal input / conjugate match to Nordic Semiconductor chips nRF24LE1 QFN32,
nRF24AP2-1CH, nRF24AP2-8CH, nRF51422-QFAA and nRF51822-QFAA
Low insertion loss
Low amplitude imbalance
Low phase imbalance
Small footprint: < 1.5 mm
2
Benefits
Very low profile: < 595 µm after reflow
High RF performance
RF BOM and area reduction
Applications
2.45 GHz impedance matched balun filter
Optimized for Nordic's chip set nRF24LE1/AP2 and nRF51 series
1.2
Description
STMicroelectronics BAL-NRF01D3 is an ultra miniature balun. The BAL-NRF01D3
integrates matching network and harmonics filter. Matching impedance has been
customized for the following Nordic Semiconductor circuits: nRF24LE1 QFN-32 pins,
nRF24AP2-1CH, nRF24AP2-8CH, nRF51422-QFAA and nRF51822-QFAA.
The BAL-NRF01D3 uses STMicroelectronics IPD technology on non-conductive glass
substrate which optimize RF performances.
The BAL-NRF01D3 has been tested and approved by Nordic Semiconductor in their
nRF2723 and nRF2752 nRFgo modules.
1.3
Flip chip package
Figure 1. Package 5 bumps
Figure 2. Pin out diagram (top view)
3
2
1
DIFF
GND
A
SE
B
C
DIFF
VCC
Lead-free Flip-Chip package
5 bumps
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DocID023194 Rev4
AN4111
Benefits of BAL-NRF01D3 reference design
2
Benefits of BAL-NRF01D3 reference design
Figure 3. Traditional discrete solution for nRF24LE1
C2
15pF
C1
15pF
X1
16MHz
P1.5 1.6
P
P0.0 0.1
R2
0R
Ain0
P4
32.768kHz
2
1
GND
VCC_nRF
C11
100nF
C17
R1
15pF
32
30
31
29
28
27
26
25
2
4
6
X2
C18
15pF
1
2
3
4
5
6
7
8
GND
22k 1%
U1
GND
1
3
5
P
R3
0R
Ain1
P0.0
XC1
XC2
P1.6
P1.5
VDD
VSS
IREF
Balun + Filter
24
23
22
21
20
19
18
17
L3
4.7n
L1
6.8n
L2
6.8n
C3
2.2nF
C4
NA
GND
GND
C5
1.5p
C6
GND
1.0p
J1
VCC_nRF
C9
100nF
GND
C7
100nF
C8
33nF
P0.2
R4
0.3
PROG
P
R5
0R
0R
Ain2
Ain3
P0.1
VDD
DEC1
DEC2
P0.2
PROG
P0.3
VSS
nRF24LE1
VDD
VSS
ANT2
ANT1
VDD_PA
RESET
P1.4
P1.3
GND
GND
GND
VCC_nRF
VDD
P0.4
P0.5
P0.6
P0.7
P1.0
P1.1
P1.2
9
10
11
12
13
14
15
16
nRF24LE1F16Q32
GND
GND
P0.4
R6
R7
P0.5
R8
P0.6
P0.7
R9
P1.0
R10
P1.1
R11
P1.2
R12
P1.3
P1.4
RESET
Figure 4. nRF24LE1 solution using BAL-NRF01D3
C2
15pF
C1
15pF
X1
16MHz
0R
0R
0R
0R
0R
0R
0R
C10
33nF
Ain4
Ain5
Ain6
Ain7
Ain8
Ain9
Ain10
P1.5
P1.6
P0.0
R2
0R
Ain0
P4
32.768kHz
2
1
GND
VCC_n
RF
C11
100nF
C17
R1
15pF
32
30
31
29
28
27
26
25
2
4
6
X2
C18
15pF
1
2
3
4
5
6
7
8
GND
22k 1%
U1
GND
1
3
5
P0.1
VCC_n
RF
R3
0R
Ain1
P0.0
XC1
XC2
P1.6
P1.5
VDD
VSS
IREF
C9
100nF
GND
C7
100nF
C8
33nF
P0.2
R4
PROG
P0.3
R5
0R
0R
Ain2
Ain3
P0.1
VDD
DEC1
DEC2
P0.2
PROG
P0.3
VSS
nRF24LE1
24
VDD
2
VSS 3
2
ANT2 2
21
ANT1
20
VDD_PA
19
RES
ET
1
P1.4 8
17
P1.3
BAL-NRF01D3
U2
2
1
3
ANT1
SE
ANT2
VDD_PA GND
5
4
GND
C3
2.2nF
C4
NA
GND
GND
J1
GND
GND
GND
VCC_n
RF
VDD
P0.4
P0.5
P0.6
P0.7
P1.0
P1.1
P1.2
9
10
11
12
13
14
15
16
nRF24LE1F16
Q32
GND
GND
R6
P0.4
P0.5
R7
P0.6
R8
R9
P0.7
P1.0
R10
P1.1
R11
P1.2
R12
P1.3
P1.4
RESET
Using BAL-NRF01D3
no external components
are required for matching and for harmonic
filtering. Only a 2.2 nF external capacitor is required for V
DD
decoupling. The test board for
nRF24LE1 is shown in
Figure 8.
DocID023194 Rev4
0R
0R
0R
0R
0R
0R
0R
C10
33nF
Ain4
Ain5
Ain6
Ain7
Ain8
Ain9
Ain10
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Benefits of BAL-NRF01D3 reference design
Figure 5. Traditional discrete solution for nRF51822
AN4111
Figure 6. nRF51822 solution using BAL-NRF01D3
Using BAL-NRF01D3 only a 0.8 pF capacitor is needed for molding and for harmonic
filtering. A 2.2 nF external capacitor is required for V
DD
decoupling. The test board for
nRF51822 is shown in
Figure 14.
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Benefits of BAL-NRF01D3 reference design
Figure 7
demonstrates two essential benefits of the BAL-NRF01D3.
Decrease in the BOM count by 80%, from 5 components to 1 component
More than 80% PCB area reduction compared to the traditional discrete solution
Figure 7. PCB area comparison between BAL-NRF01D3 and discrete solution
“Traditional” discrete solution
BAL-NRF01D3 solution
Compared to discrete solutions, the BAL-NRF01D3 solution is much easier to implement.
Thanks to this smart implementation:
No RF measurement tools and RF skills are required to design and validate the
function.
Performance is less sensitive to component placement.
PCB design is symmetrical from differential output to antenna, providing much shorter
traces between transceiver outputs to the balun.
As a result, ST BAL-NRF01D3 reduces harmonics generation.
DocID023194 Rev4
5/17
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