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AN RFMD® APPLICATION NOTE
SZA-2044 Biasing, VPC Selection, and
Performance versus Supply Voltage
RFMD Multimarket Products Group
Overview
The SZA-2044 is a very flexible amplifier in terms of biasing. It can run deep class AB for best efficiency and up to near class A
for best linearity. The power on/off control voltages are accessible for each of the three stages and nominal currents are set
via externally chosen series resistors for each stage. It can support power on voltage logic (VPC) from +2.9V to +5V by simply
choosing the right resistor network for the desired quiescent current and VPC power enable voltage. This application note
addresses VPC resistor selection, VPC voltage selection, associated performance tradeoffs of the various configurations over
temperature, and performance over supply voltage variation.
VPC Power Enable Bias Resistor Selection for Various VPC Voltage Levels
Information is shown below for the recommended IQ setting of 302mA for V+=VCC =5V. Table 1 shows resistor values for
VCC =5V and VPC range of 2.9V–5V. Table 2 shows resistor values for other VCC and VPC level combinations.
Figure 1. Application Schematic
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AN068 090319
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or [email protected]
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SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage
Table 1
VPC =2.9V to 5.0V
VCC =5.0V
ICQ=302mA
Stage 1 (75mA)
Stage 2 (227mA)
VPC
R1 (Ω)
R2 (Ω)
R5 (Ω)
2.9
34.8
27.4
OUT
3
121
105
OUT
3.1
205
182
OUT
3.2
287
261
OUT
3.3
374
332
OUT
5
1.82K
1.10K
4.75K
Table 2
ICQ=302mA
Stage 1 (75mA)
Stage 2 (227mA)
VCC =4.9V to 5.5V
VPC =2.9V to 5V
3.3
2.9
10
0
OUT
3.3
3
82.5
68.1
OUT
3.3
3.1
165
140
OUT
3.3
3.2
243
200
OUT
3.3
3.3
316
274
OUT
4.8
5
1.78K
1.10K
4.75K
4.9
2.9
33.2
24.3
OUT
R1 (Ω)
R2 (Ω)
R5 (Ω)
4.9
3
118
100
OUT
4.9
3.1
200
178
OUT
4.9
3.2
280
255
OUT
4.9
3.3
365
332
OUT
4.9
5
1.82K
1.10K
4.75K
5
2.9
34.8
27.4
OUT
5
3
121
105
OUT
5
3.1
205
182
OUT
5
3.2
287
261
OUT
5
3.3
374
332
OUT
5
5
1.82K
1.10K
4.75K
5.1
2.9
37.4
29.4
OUT
5.1
3
124
107
OUT
5.1
3.1
210
187
OUT
5.1
3.2
294
267
OUT
5.1
3.3
374
340
OUT
5.1
5
1.82K
1.13K
4.75K
5.2
2.9
39.2
32.4
OUT
5.2
3
124
110
OUT
5.2
3.1
210
191
OUT
5.2
3.2
294
267
OUT
5.2
3.3
383
348
OUT
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support, contact RFMD at (+1) 336-678-5570 or [email protected]
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SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage
Table 2
5.2
5
1.82K
1.15K
4.75K
5.3
2.9
41.2
34
OUT
5.3
3
127
113
OUT
5.3
3.1
215
196
OUT
OUT
5.3
3.2
301
274
5.3
3.3
383
357
OUT
5.3
5
1.82K
1.15K
4.75K
5.4
2.9
43.2
37.4
OUT
5.4
3
130
118
OUT
5.4
3.1
215
196
OUT
5.4
3.2
301
280
OUT
5.4
3.3
392
357
OUT
5.4
5
1.87K
1.15K
4.75K
5.5
2.9
46.4
39.2
OUT
5.5
3
133
121
OUT
5.5
3.1
221
200
OUT
5.5
3.2
309
280
OUT
5.5
3.3
392
365
OUT
5.5
5
1.87K
1.18K
4.75K
The temperature range and required performance of the application should be considered when choosing a VPC power enable
voltage. The higher VPC values have better performance over temperature because Iq varies less with temperature. Figure 2
shows Iq variation over temperature for VPC enable set voltages ranging from 2.9V to 5V.
.
SZA-2044 Icq vs Vpc vs Temp.
450
400
Vpc(V)
Icq(mA)
350
2. 9v
3. 0v
300
3. 1v
250
3. 2v
3. 3v
200
5v
150
100
-45 -35 -25 -15 -5
5
15 25 35 45 55 65 75 85 95
Temp(C)
Figure 2. SZA-2044 ICQ versus VPC versus Temperature
AN068 090319
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or [email protected]
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SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage
Another consideration is the variation in VPC enable voltage and the impact on performance. Performance is optimized when
the VPC power enable is regulated and controlled. Figure 3 shows IQ versus swept VPC for the nominal cases of VPC
enable=2.9V to 5V at 25°C.
.
SZA-2044 Icq vs swept Vpc, Constant Vcc=5V, T=25C
(Icq=302mA)
0.5
0.4
Icq(A)
0.3
0.2
0.1
0
0
Vpc
Config.
1
2
3
4
5
6
VPC(V)
2.9v
3.0v
3.1v
3.2v
3.3v
5v
Figure 3. SZA-2044 ICQ versus Swept VPC, Constant VCC =5V, T=25°C
The variation in current over temperature has impact on EVM over temperature. Figure 4 shows the EVM at POUT =22.5dBm
versus temperature and VPC enable set voltage.
.
EVM(%) @ Pout=22.5dBm vs Vpc vs Temp,
F=2.4GHz
5.0
EVM(%)
4.0
3.0
2.0
1.0
-45 -35 -25 -15 -5
5
15
25
35
45
55
65
75
85
95
Temp(C)
Vpc Config.
2.9v
3v
3.3v
5v
Figure 4. EVM (%) at POUT =22.5dBm versus VPC versus Temp, F=2.4GHz
AN068 090319
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or [email protected]
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SZA-2044 Biasing, VPC Selection, and Performance versus Supply Voltage
The variation in VCC also has an impact on EVM. Figure 5 shows the POUT at 3% EVM versus temperature and fixed VPC
voltage=5.0V.
.
Pout @ 3% EVM vs Vcc, F=2.4GHz, Constant Vpc=5V,
Icq=302mA
25
24. 5
Pout(dBm)
24
23. 5
23
22. 5
22
21. 5
21
4.8
4.9
5
5. 1
5.2
5.3
5.4
5.5
Vcc(V)
-40c
-20c
0c
+25c
+70c
+85c
Figure 5. POUT at 3% EVM versus VCC, F=2.4GHz, Constant VPC =5V, ICQ=302mA
AN068 090319
7628 Thorndike Road, Greensboro, NC 27409-9421 · For sales or technical
support, contact RFMD at (+1) 336-678-5570 or [email protected]
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