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!