Push-Pull High IP2 Amplifiers

DESIGN APPLICATION NOTE --- AN025
Push-Pull High IP2 Amplifiers
Abstract:
With the abundance of data and voice traffic being transmitted across standard cable and wireless pathways and the
ever increasing linearity requirements of CATV amplifiers, there is a great need for amplification that optimizes gain,
VSWR, efficiency and linearity. This application note demonstrates how to use two NGA-486 amplifiers in a pushpull configuration with better than +65 dBm IP2 performance across the 50-860 MHz band. A lower cost push-pull
option, the SGA-6289, is presented with better than +60 dBm IP2 from 50-860 MHz.
Introduction:
Inherent in push-pull amplifiers is the distinct cancellation of second order harmonics and intermodulation products.
The low cost of RFMD amplifiers, coupled with their excellent linearity, makes them an easy choice
for use in these high linearity CATV applications. A summary of performance of the NGA-486 and SGA-6289 pushpull amplifiers is shown in Table 1 and Figures 1 and 2 below. All measurements in this Application Note were taken
in a 75 Ohm system.
Summary Table
Measured Performance in
Push-Pull Configuration
Parameter
NGA-486
SGA-6289
IP2 (dBm)
70
62
IP3 (dBm)
38
36
P1dB (dBm)
20
20
Gain (dB)
13.5
13.5
Input Return Loss (dB)
15
18
Output Return Loss (dB)
15
15
80
80
75
75
70
70
IP2 (dBm)
IP2 (dBm)
Table 1: Typical Performance Summary of Push-Pull
Configured Amplifiers
65
60
55
50
60
55
50
0 dB m
4 dB m
45
65
0 dB m
4 dB m
45
40
40
0
0 .2
0 .4
0 .6
0 .8
1
0
0 .2
0 .4
0 .6
0 .8
1
Frequency (GHz)
Frequency (GHz)
Figure 1: NGA-486 Second Order Intercept
vs. Pout/Tone Push-Pull, 1 MHz Spacing
Figure 2: SGA-6289 Second Order Intercept
vs. Pout/Tone Push-Pull, 1 MHz Spacing
The information provided herein is believed to be reliable at press time. RFMD assumes no responsibility for inaccuracies or omissions. RFMD assumes no responsibility for
the use of this information, and all such information shall be entirely at the user’s own risk. Prices and specifications are subject to change without notice. No patent rights or licenses to any of the circuits described
herein are implied or granted to any third party. RFMD does not authorize or warrant any RFMD product for use in life-support devices and/or systems.
Copyright 2002 RFMD All worldwide rights reserved.
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EAN-101763 Rev B
DESIGN APPLICATION NOTE --- AN025
Push-Pull High IP2 Amplifiers
Measurement Results for InGaP HBT NGA-486.
The NGA-486 was tested for IP2 performance in both single ended and push-pull configurations. One device was
measured in the single ended configuration and two in the push-pull configuration. The push-pull devices have
excellent IP2 performance, well exceeding typical CATV specification requirements of +60 dBm over the entire cable
band. The basic amplifier building block for the push-pull configuration is shown in Figures 3 and 4. The push-pull
configuration is shown in Figures 5 and 6.
Vs = 8.0V
VS
Rbias = 39Ω
0.01µF
1000pF
68pF
.01uF
1000pF
68pF
D UT
220nH
1000pF
1000pF
220 nH
NGA-486
OUT
IN
1000 pF
ECB-100330
86 Eval Board
1000 pF
Figure 3: NGA-486 Singled Ended Schematic
Figure 4: NGA-486 Singled Ended PCB Layout
Vs = 8V
Rbias = 39Ω
0.01µF
1000pF
68pF
Si
86 Package Push Pull
.01uF
1000pF
68pF
Wideband Balun
NGA-486
220 nH
RF OUTPUT
DUT
220nH
3
1
1000pF
1000pF
Primary
Primary
68pF
1
1000pF
DUT
Rbias = 39Ω
0.01µF
1000pF
5
Vs = 8V
Macom
ETC1-1-13
2
2
4
5
ETC1-1-13 Balun
1000pF
3
ETC1-1-13 Balun
RF INPUT
4
1000 pF
1000 pF
Secondary
Secondary
220nH
Macom
ETC1-1-13
NGA-486
68uF
1000pF
.01uF
220 nH
MA1
1000 pF
1000 pF
Figure 5: NGA-486 Push-Pull Schematic
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Figure 6: NGA-486 Push-Pull PCB Layout
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EAN-101763 Rev B
DESIGN APPLICATION NOTE --- AN025
Push-Pull High IP2 Amplifiers
Tables 2 and 3 illustrate IP2 performance of the NGA-486 at 5 frequency pairings. Two spacings yield a 54 MHz
tone and and three spacings yield an 860 MHz tone. These tables represent the performance of one singleended and one push-pull amplifier across the 50-860 MHz CATV band. This shows that the IP2 performance of
the push-pull configuration is much improved over that of the single ended devices.
80
Freq. Pairs (MHz )
75
IM (dBc)
IM (dBc)
IP2 (dBm)
IP2 (dBm)
IM2 Freq. 0 dBm/tone 4 dBm/tone 0 dBm/tone 4 dBm/tone
553.25
499.25
54
56.2
51.5
56.2
55.5
865.25
811.25
54
52.9
48.2
52.9
52.2
427.25
433.25
860.5
56.3
52
56.3
56
327.25
533.25
860.5
55.1
51
55.1
55
227.25
633.25
860.5
54
50.2
54
54.2
70
IP2 (dBm)
Single Ended
65
60
55
50
+4 dBm
0 dBm
45
40
0
0 .2
0 .4
0 .6
0 .8
1
Frequency (GHz)
Table 2: Single Ended NGA-486 IP2 Summary
Figure 7: Single Ended NGA-486 IP2 vs.
Pout/Tone Push-Pull, 1 MHz Spacing
80
Freq. Pairs (MHz )
75
IM (dBc)
IM (dBc)
IP2 (dBm)
IP2 (dBm)
IM2 Freq. 0 dBm/tone 4 dBm/tone 0 dBm/tone 4 dBm/tone
70
IP2 (dBm)
Push-Pull
65
553.25
499.25
54
81.2
81.9
81.2
85.9
865.25
811.25
54
69.1
64.4
69.1
68.4
427.25
433.25
860.5
75.6
73.3
75.6
77.3
327.25
533.25
860.5
71.8
67.5
71.8
71.5
50
227.25
633.25
860.5
80.5
75.5
80.5
79.5
45
60
55
+4 dBm
0 dBm
40
0
0.2
0.4
0.6
0.8
1
Frequency (GHz)
Table 3: Push-Pull NGA-486 IP2 Summary
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Figure 8: Push-Pull NGA-486 IP2 vs.
Pout/Tone Push-Pull, 1 MHz Spacing
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EAN-101763 Rev B
DESIGN APPLICATION NOTE --- AN025
Push-Pull High IP2 Amplifiers
Figure 9 illustrates that there is a 2 dB improvement in P1dB when comparing a push-pull configuration to a single
device. The high insertion loss of many wideband baluns prevents realization of the theoretical 3 dB P1dB
advantage. The balun used for these measurements (MACOM ETC1-1-13) has between .35 dB and .9 dB insertion
loss across the CATV band.
Figure 10 shows the excellent third order linearity performance of the push-pull amplifiers. Both push-pull amplifiers
were tested at +6 dBm output power per tone (about 15 dB below the P1dB point).
30
50
P u s h -P u ll, P 1 d B
S in g le E n d e d , P 1 d B
28
26
46
OIP3 (dBm)
P1dB (dBm)
P us h-P ull, + 6 d B m , 7 5 o hm
48
24
22
20
18
16
44
42
40
38
36
14
34
12
32
10
30
0
0 .2
0 .4
0 .6
0 .8
1
0
0 .2
0 .4
0 .6
0 .8
1
Frequency (GHz)
Frequency (GHz)
Figure 9: NGA-486 Push-Pull vs.
Single Ended P1dB
Figure 10: NGA-486 Push-Pull
IP3 vs. Frequency
0
20
18
16
14
12
10
8
6
4
2
0
Return Loss (dB)
Gain (dB)
The Gain response of the NGA-486 push-pull amplifier is shown in Figure 11. Input and Output return loss of this
amplifier is illustrated in Figure 12. Notice the wide bandwidth of the return loss of the amplifier configured this way.
-5
-1 0
Output RL
-1 5
Input RL
-2 0
-2 5
-3 0
0
0 .2
0 .4
0 .6
0 .8
1
0
0 .4
0 .6
0 .8
1
Frequency (GHz)
Frequency (GHz)
Figure 11: NGA-486 Push-Pull Gain
vs. Frequency
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0 .2
Figure 12: NGA-486 Push-Pull IRL and ORL
vs. Frequency
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EAN-101763 Rev B
DESIGN APPLICATION NOTE --- AN025
Push-Pull High IP2 Amplifiers
Measured Data for SiGe HBT SGA-6289
The configurations of the SGA-6289 single ended amplifier is shown in Figures 13 and 14. The push-pull schematic
and layout are shown in Figures 15 and 16.
Vs = 7.5V
Rbias = 47Ω
0.01µF
1000pF
.01uF
68pF
1000pF
68pF
D UT
220nH
1000pF
1000pF
220 nH
SGA-6289
OUT
IN
1000 pF
ECB-100331
SOT-89 Eval Board
1000 pF
Figure 13: SGA-6289 Single Ended Schematic
Figure 14: SGA-6289 Single Ended PCB Layout
Vs = 7.5V
Rbias = 47Ω
0.01µF
1000pF
68pF
.01uF
1000pF
68pF
89 Package Push Pull
Wideband Balun
SGA-6289
220 nH
RF OUTPUT
DUT
220nH
3
1
1000pF
1000pF
1000pF
Rbias = 47Ω
0.01µF
1000pF
1
Secondary
Secondary
Macom
ETC1-1-13
SGA-6289
Primary
DUT
Primary
68pF
5
Vs = 7.5V
Macom
ETC1-1-13
2
2
4
5
ETC1-1-13 Balun
1000pF
3
ETC1-1-13 Balun
RF INPUT
4
1000 pF
1000 pF
220nH
68uF
1000pF
.01uF
220 nH
MA1
1000 pF
1000 pF
Figure 15: SGA-6289 Push-Pull Schematic
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Figure 16: SGA-6289 Push-Pull PCB Layout
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EAN-101763 Rev B
DESIGN APPLICATION NOTE --- AN025
Push-Pull High IP2 Amplifiers
The SGA-6289 IP2 performance is shown in Tables 4 and 5 and Figures 17 and 18. The push-pull amplifier’s IP2 is
greater than +60 dBm across the band. As mentioned before this device has the advantage of low bias current and
excellent linearity at a very low price. Again, notice the significant IP2 advantage gained when the push-pull
configuration is used.
70
Freq. Pairs (MHz )
553.25
499.25
IM (dBc)
IM (dBc)
IP2 (dBm)
IP2 (dBm)
IM2 Freq. 0 dBm/tone 4 dBm/tone 0 dBm/tone 4 dBm/tone
54
48.4
44.5
48
48
65
IP2 (dBm)
Single Ended
60
55
50
865.25
811.25
54
47.6
43.7
47.6
47.7
427.25
433.25
860.5
48
44.1
48
48
327.25
533.25
860.5
47.3
43.5
47.3
47.5
40
227.25
633.25
860.5
47.6
43.6
47.6
47.6
35
45
+4 dBm
0 dBm
30
0
0.2
0.4
0.6
0.8
1
Frequency (GHz)
Table 4: Single Ended SGA-6289 IP2 Summary
Figure 17: SGA-6289 IP2 vs. Pout/Tone
Single Ended, 1 MHz Spacing
70
Freq. Pairs (MHz )
IM (dBc)
IM (dBc)
IP2 (dBm)
IP2 (dBm)
IM2 Freq. 0 dBm/tone 4 dBm/tone 0 dBm/tone 4 dBm/tone
553.25
499.25
54
72.4
68.2
72.4
72.2
865.25
811.25
54
62.8
58.9
62.8
62.9
427.25
433.25
860.5
68.2
64
68.2
68
327.25
533.25
860.5
65.3
61.7
65.3
65.7
227.25
633.25
860.5
69.5
65.2
69.5
69.2
65
IP2 (dBm)
Push-Pull
60
55
50
45
40
+4 dBm
0 dBm
35
30
0
0.2
0.4
0.6
0.8
1
Frequency (GHz)
Table 5: Push-Pull SGA-6289 IP2 Summary
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Figure 18: SGA-6289 IP2 vs. Pout/Tone
Push-Pull, 1 MHz Spacing
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EAN-101763 Rev B
DESIGN APPLICATION NOTE --- AN025
Push-Pull High IP2 Amplifiers
Figure 19 compares the 1dB compression point of a push-pull and single ended amplifier. Figure 20 shows the
excellent third order linearity performance of the push-pull amplifier at +6 dBm output power per tone (about 15
dB below the P1dB point).
SGA-6289 Push Pull IP3 vs. Frequency
OIP3 (dBm)
P1dB (dBm)
SGA-6289 Push Pull P1dB
24
23
22
21
20
19
18
17
16
15
14
P u s h -P u ll, P 1 d B
S in g le E n d e d , P 1 d B
0
0 .2
0 .4
0 .6
0 .8
40
38
36
34
32
30
28
26
24
22
20
1
Push-Pull, +6 dBm, 75 Ohm
0
0.2
0.4
0.6
0.8
Frequency (GHz)
Frequency (GHz)
Figure 19: SGA-6289 Push-Pull
vs. Single Ended P1dB
Figure 20: SGA-6289 Push-Pull IP3
vs. Frequency
1
The gain response of the SGA-6289 push-pull amplifier is shown in Figure 21, input and output return loss are shown
in Figure 22. Notice the wide bandwidth of the return loss configured this way.
20
0
18
-5
Ret. Loss (dB)
Gain (dB)
16
14
12
10
8
-10
Output RL
-15
-20
Input RL
-25
6
-30
4
0
0 .2
0 .4
0 .6
0 .8
1
0
0 .2
0 .4
0 .6
0 .8
1
Frequency (GHz)
Frequency (GHz)
Figure 21: SGA-6289 Push-Pull Gain
vs. Frequency
Figure 22: SGA-6289 Push-Pull IRL and ORL
vs. Frequency
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DESIGN APPLICATION NOTE --- AN025
Push-Pull High IP2 Amplifiers
NGA-486 and SGA-6289 CSO, CTB and XMOD Measurement Results.
The CSO results for both SGA-6289 push-pull amplifiers were better than 75 dBc at the +25 and +34 dBmV output
power level per tone as shown in Figures 23 and 24. The push-pull SGA-6289 far exceeded the –70 dBc requirement
and the CSO was immeasurable at many of the channels. CTB was better than 68 dBc across the band and XMOD
was better than 62 dBc across the band.
The power per tone was held constant for the devices at +25 and +34 dBmV into 75 ohms. 79 level channels were
used for the measurements.
The NGA-486 CSO and CTB results were outstanding as illustrated in Figures 25 and 26. CSO was better than 80
dBc across the band and CTB and XMOD were better than 68 dBc across the band at +34 dBmV per channel for 79
channels.
100
90
90
80
80
dBc
110
100
dBc
110
70
60
70
60
50
C TB
C SO-
C SO+
X mod
40
C SOX mod
40
0
100
200
300
400
500
600
0
110
100
100
90
90
80
80
dBc
110
70
60
50
C TB
C SO-
C SO+
X mod
100
200
400
500
600
70
60
50
40
300
Frequency (MHz)
Figure 24: SGA-6289 Push-Pull CTB/CSO/XMOD
8V/150mA, 34 dBmV/Ch., 79 Ch., Flat
Frequency (MHz)
Figure 23: SGA-6289 Push-Pull CTB/CSO/XMOD
8V/150mA, 25 dBmV/Ch., 79 Ch., Flat
dBc
C TB
C SO+
50
C TB
C SO-
C SO+
X mod
40
0
100
200
300
400
500
600
Frequency (MHz)
Figure 25: NGA-486 Push-Pull CTB/CSO/XMOD
8V/160mA, 25 dBmV/Ch., 79 Ch., Flat
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0
100
200
300
400
500
600
Frequency (MHz)
Figure 26: NGA-486 Push-Pull CTB/CSO/XMOD
8V/160mA, 34 dBmV/Ch., 79 Ch., Flat
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