Huawei and the University of Pavia present a SiGe power amplifier at 80GHz. A common-base output stage causes the DC current to track the signal current and improve efficiency at back-off power. Realized prototype shows OP1dB of 18dBm with Psat of 19dBm. The efficiency at OP1dB and at 6dB are 22% and 8.5%, respectively.

1. A SiGe BiCMOS E-Band Power Amplifier
with 22% PAE at 18dBm OP1dB and 8.5%
at 6dB Back-Off Leveraging Current
Clamping in a Common-Base Stage
J. Zhao1,2, E. Rahimi1, F. Svelto1, A. Mazzanti1
1University of Pavia, Pavia, Italy
2HiSilicon-Technologies, Milan, Italy

2. Outline
• Motivations
• Current-clamping to improve back-off efficiency for
mm-Wave PAs
• Measurement Results
• Conclusions
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

3. Motivations
• 5G requires high-capacity, high-density, and low-cost backhaul
• 10 GHz spectrum available at E-band (71-76GHz, 81-86GHz)
• Silicon based transceivers reduce costs
[IEEE Network 2014]
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Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

4. Average efficiency of PAs
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𝑃𝐴𝐸 =
𝑃 𝑂𝑈𝑇 − 𝑃𝐼𝑁
𝑃 𝑆𝑈𝑃𝑃𝐿𝑌
=
1 −
1
𝐺 𝑃
𝑃 𝑂𝑈𝑇
𝑉 𝑆𝑈𝑃𝑃𝐿𝑌 𝐼 𝑆𝑈𝑃𝑃𝐿𝑌
@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage
• Average efficiency is critical
• PAE at 6dB back-off in silicon E-band PAs is 1-3% only
• Can be improved by scaling supply voltage and
current with POUT
• Wideband voltage modulators are power hungry
• Current modulation is more suitable for mm-Wave

5. Supply current modulation
• Class-B features 𝐼𝑆𝑈𝑃𝑃𝐿𝑌 ∝ 𝐼 𝑅𝐹, but suffers from low
gain and low linearity
• Current clamping is proposed for ISUPPLY modulation,
yielding superior gain, linearity and efficiency
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

6. Clamping technique
Voltage clamping : 𝑉 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 ∝ 𝑉 𝑅𝐹
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

7. Current clamping
Voltage clamping : 𝑉 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 ∝ 𝑉 𝑅𝐹
Current clamping is the dual
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

8. Current clamping
Voltage clamping : 𝑉 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 ∝ 𝑉 𝑅𝐹
Current clamping is the dual: 𝐼 𝑎𝑣𝑒𝑟𝑎𝑔𝑒 ∝ 𝐼 𝑅𝐹
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

9. Current clamping in Common-Base
CBE = 0
LECBE=1/ω2
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@ 2017 IEEE International Solid-State Circuits
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2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage
Ipk
-Ipk
0
2Ipk
IE
IIN
IL

10. • Average current of Q1 tracks quickly the
envelope of IIN
• 50% supply current (and power) saving
compared to Class-A biasing
Current clamping with AM input
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2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage
fCarrier = 80GHz, fAM= 5GHz
IINandIL(mA)

11. Common-Base vs Common-Emitter
C.B. and C.E. configurations behave very differently
C.B. enjoys:
• higher breakdown voltage  higher PSAT and efficiency
• flat curves and very linear current gain  OP1dB near PSAT
@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage
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1.6V
Common
Emitter (C.E.)
VCE [V]
IC[mA]
Common
Base (C.B.)
3.4V VCB [V]
IC[mA]

12. Schematic of two-stage PA
• Common-Base output stage with current clamping
• Near 20dBm PSAT without power combining
• Cascode driver in Class-A for high linearity
• Inter-stage matching (T2) introduces ~x3 current-gain
2.3V 1.8V
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

13. Chip photograph
ST SiGe BiCMOS 55nm with fT=320GHz, fMAX=370GHz
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

14. S-Parameter measurements
• Peak gain = 21dB at 80GHz
• 3dB bandwidth from 71-86GHz
• Unconditionally stable
S11
S22
S21
S12
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

15. Large-signal performances @ 80GHz
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage
• OP1dB=18dBm, only 1dB lower than PSAT=19dBm
• PAE @ OP1dB = 22% , PAE @ OP1dB-6dB = 8.5%
Gain
PAE
18dBm

16. 0
20
40
60
80
100
120
140
0 5 10 15 20
DCCurrent[mA]
Output Power [dBm]
Large-signal measurements @ 80GHz
ISUPPLY of output stage tracks well Pout and reduces to half
from OP1dB to 6dB back-off
Output stage
DC current
Driver DC
current
∝ 𝐏 𝐨𝐮𝐭
OP1dBOP1dB-6dB
16 of 20
@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

17. Large-signal performances over frequency
>17dBm OP1dB and >20% PAE from 70-90GHz
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

18. Comparison with State-of-the-art
2× or higher efficiency, both at OP1dB and 6dB B.O.
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@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

19. Conclusions
• Current-clamping in Common-Base is investigated
for ISUPPLY modulation, yielding PAE improvement at
back-off
• A two-stage E-band SiGe BiCMOS PA features
PSAT=19dBm with OP1dB=18dBm (only 1dB distance)
• PAE @ OP1dB = 22% , PAE @ OP1dB-6dB = 8.5%,
remarkably higher than previously reported silicon
PAs at E-band
19 of 20
@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage

20. Acknowledgments
• Authors thank the RF Dept. of HiSilicon for
technical and financial support
• Authors thank the Huawei Milan - Italy for the
assistance with measurements.
20 of 20
@ 2017 IEEE International Solid-State Circuits
Conference
2.6: A SiGe BiCMOS E-Band Power Amplifier with 22% PAE at 18dBm OP1dB and 8.5% at
6dB Back-Off Leveraging Current Clamping in a Common-Base Stage