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A 0.8-1.8 GHz Wideband Low Noise Amplifier with Capacitive Feedback
Toshihiko Ito,Kenichi Okada,and Akira Matsuzawa
Tokyo Institute of Technology, Japan
1Contents
• Background• Conventional common-gate topologies• Proposed LNA• Simulation and measurement results• Conclusion
2Necessity of multi standard
RF front-end
A/D,D/Aconverter
DSP
Controller
Software
Software defined radio
LNA MixerBPF SAW
BPF SAWBPF SAW
BPF SAW
• Several RFICs are required for each wireless communication standard.
• To improve this situation, SDR is proposed.
Large area, power and cost
3Requirements for SAW-less receiver
GLNA =15dBIIP3LNA=-6dBmNFLNA=2.2dB
GMixer =10dBIIP3Mixer=0.5dBmIIP2Mixer=60dBm
GFilterTx=-20dBGFilterRx=0dBIIP3filter=10.5dBm
NF=3dB
•Assuming that on chip notch filter is used instead of SAW filters.
•When Tx leak=-30dBm and CW blocker=-60dBm, requirements for components are calculated as follows.
4Topology of LNAs
• Resistive feedback LNA– High gain, low noise– Large power
• Common-gate LNA– High linearity, low power– Lower gain, higher noise than
resistive feedback LNACommon-gate topology is employed.
5Fundamental common-gate LNA
Sm
in1 R
gZ ==
dB8.24
1out
S =++=RR
F γ
• gm of the common-gate transistor is fixed due to the input impedance matching.
• NF cannot be improved due to fixed gm.
6Capacitive-Cross-Couple LNA
• This topology achieves a lower noise factor than that of fundamental one.
• However, gm and noise of common-gate transistor are still fixed.
[1] W. Zhuo, et al. ESSCIRC, 2000.
dB93.1s42
1out
=++=R
RF γ
Sm
in 21 Rg
Z ==
7Proposed topology
• The proposed LNA employs capacitive-cross-couple technique and capacitive feedback.
• gm can be enlarged, NF can be improved.
( )
( )
( ) ( )( ) ⎟
⎠⎞⎜
⎝⎛ ++
++++
++
+=
=+
=
2S
2222out
22out
2outSS
2222out
22S
2out
22
2S
22
Sm
2out
22
in
1
2
12
1
21
Re
RCRCR
RRRCRCR
RCRC
F
Rg
RCZ
ωω
ωω
ωωγ
ω
8Noise calculation
• Calculated NFs of CCC LNA and capacitive feedback LNA are compared.
• The larger C is, the lower NF is.
1.7
1.8
1.9
2
0 20 40 60 80 100
NF
[dB
]
C [fF]
ConventionalProposed
9
16182022242628
0 0.5 1 1.5 2 2.5 3
Av [d
B]
Frequency [GHz]
CalculationSimulation
Voltage gain
• The larger C is, the larger but less flatness of voltage gain is.
• Simulated result is less flat than calculated one.
22242628303234
0 0.5 1 1.5 2 2.5 3
Av [d
B]
Frequency [GHz]
100fF75fF50fF25fF
10LNA schematic including buffer
• External chip inductors are used.• CP is implemented by ESD diode.• The source follower buffer is connected
11Chip and PCB photo
• Nodes of photographs below correspond to each other.
• Core size is 0.066mm2
To Chip Inductors
RFin+
RFin-RFout-
RFout+--
DC
1.1mm
RFin+ RFin-
RFout-RFout+
DC
To chip inductors
12Measured S parameters
• S11 < -5dB and S22 < -10dB @ 0.8-1.8GHz• Maximum power gain is 13.4dB.• These are calculated from 4-port S-para.
-35
-30
-25
-20
-15
-10
-5
0
0 0.5 1 1.5 2Frequency [GHz]
S11,
S22
[dB
]
S11S22
00
3
6
9
12
15
0.5 1 1.5 2Frequency [GHz]
Gai
n[d
B]
13Measured NF
• Measured NF is 2.7dB.• This result is much higher than
simulated one.
1
1.5
2
2.5
3
3.5
4
0 0.5 1 1.5 2Frequency [GHz]
NF
[dB
]
implementation loss
Meas.Sim.
14Parasitic elements of wire and TL
• Transmission line of PCB and parasitic of bonding wire model is made.
• Inductor coupling is also considered.
0.3Ω
3nH
k=0.43
500fF 500fF
To chip inductors
RFin+
RFout+
0.3Ω
0.3Ω
3nH
3nH
500fF
500fF 500fF
500fF
3nH
3nH 0.3Ω
0.3Ω RFin-
RFout-
Chip
15NF Comparison
• Measured and simulated with parasitic model NFs are compared.
• Simulation result using parasitic model is similar to the measured result.
02
4
6
8
10
12
14
0 1
2
3
Noi
sefig
ure
[dB
]
Frequency [GHz]
LPE+PCB+wireMeasurementLPE
16Performance evaluation
• Simulation results achieve targets and NF is lower than 2dB.
• Measured results can be improved in consideration with the parasitics.
[2]S.Woo, et al. ISSCC 2009
Goal This work [2]Freq. [GHz] 0.8-2.6 0.8-1.8 0.3-0.92Gain [dB] 15 13.4 21NF [dB] 2.2 2.7 2
IIP3 [dBm] -6 -7 -3.2Pdc [mW] - 6.5 3.6
17Conclusion
• The wideband low noise amplifier with capacitive feedback is proposed.
• The capacitive feedback adds more flexibility in gm and NF can be theoretically improved.
• Measured and simulated NFs are much different from each other.
• That can be improved in consideration with the parasitic components.
18
Thank you for your attention!