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Calibration of Input-Matching and its Center Frequency for an Inductively Degenerated Low

Noise Amplifier

Laboratory of Electronics and Information TechnologiesNational school of Engineers Sfax

University of Sfax

Sami Mahersi, Hassene Mnif and Mourad Loulou

ICECS 2010, IEEE International Conference on Electronics Circuits and SystemsAthens, 12-15 December 2010

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Outline

Introduction

Technique of input matching and center frequency calibration of

an Inductively degenerated LNA

Theoretical study of the calibration technique Calibration of Input matching

Calibration of center frequency

Impact of the calibration on the LNA behaviour

Conclusion and future works

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Introduction(1)

• Several factors causes RF front-End (LNA) performance degradation:

Parasitic Effects Process variation

Power Supply voltage variation

Degrading the circuit performances

Non performant Circuitbehaviour

On-chip Capacitive couplingTemperature

Variation

Introduction(2)

Input

ADCDigital

calibration Algorithm

Sensor

Tunable LNA (Device Under

Test)Output

Sensor

DAC

Basic schema of a DUT performances Self calibration system

J. Wilson, M. Ismail, “Input match and load tank digital calibration of an inductively degenerated CMOS LNA,” Integration, the VLSI Journal, vol. 42, Issue 1, pp. 3-9, January 2009

Self Calibration systems are used for self controlling and self correcting the performances of a Device Under Test in order to compensate performances deviations

Principle: The sensors take the input and the output signals of the DUT. Transform the RF signals into DC voltage converted to digital for processing by the calibration algorithm block. The results, producing a correction signal which is fed back to the Tunable DUT.

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In This Work

A Calibration schema for a LNA performances

• We propose a new technique to tuning two performances of an Inductively Degenerated low noise amplifier which are : the input matching and center frequency.

• The purpose is to have separate control of both characteristics

• Low impact on Amplifier other characteristics: Gain, Linearity and Noise Figure

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Technique of input match and its center frequency calibration for an Inductively degenerated LNA

Theoretical study of the calibration technique

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Schematic of LNA for calibration

RL=50Ω

VDD

Vout

Ls

Lg

M1

M2

Ld Cd

Rs= 50Ω

Vs

Zin

Cg

Cs

Cc1

Cc2

R2

R1

Zout

M3

Zin

fc

• Cs capacitor for the tuning of input matching

• Cg capacitor in parallel with Ls forthe tuning of the central frequency

Advantages compared to already proposed techniques:

• Avoid the use of the inductance tuning (complexity in the implementation)

• Having independant tuning of the parameters S12 and fo)

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501

)Re(2

gsss

smin

CCL

LgZ

totssgtotgsgss CCLLCLCLCLf

111

22

10

totssgsstotstotg CCLLCLCLCL 42 Where :

gsgtot CCC

111Where :

01

1)Im(

2

totss

sgin

CCL

LLZ

Symbolic analysis of Input impedance and resonance frequency

gsss

sm

totss

sgin

CCL

Lg

CCL

LLjZ

22 1

1

1

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Variation of resonance frequency versus the capacitors Ctot and Cs

80 85 90 95 100 105 110 115 12090

95

100

105

110

115

Ctot, Cs (%)

f0 (

%)

Cs

Ctot

• The central frequency is more dependant on the Ctot (Cg) variation • However it doesn’t vary when Cs varies

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Variation of input impedance versus capacitor Cs for different values gm and Ls

500 1000 1500 2000 2500 300042

44

46

48

50

52

54

56

58

60

Cs (fF)R

eal(Z

in)

(Ohm

)

Ls=35.971e-2 nH

Ls=37.572e-2 nHLs=39.323e-2 nH

100 200 300 400 500 600 700 800 900 100044

46

48

50

52

54

56

58

Cs (fF)

Rea

l(Zin

) (O

hm)

gm = 70e-3 A/V

gm = 35e-3 A/V

gm = 15e-3 A/V

• Decreasing gm makes the tuning range of the input impedance more wider• Decreasing Ls makes the tuning range of the input impedance more wider.

This is to be considered when designing the LNA and a compromise can be reached when setting the values of gm and Ls

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Technique of input matching and its center frequency calibration for an Inductively degenerated LNA

Calibration of Input matching

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Initial performances of LNA at 2.45GHz

Parameter Value

S21 (dB) 20.5

S11 (dB) -58.6

Real(Zin) (Ω) 50.09

Imag(Zin) (Ω) -0.07

S22 (dB) -47.6

Real(Zout) (Ω) 49.6

Imag(Zout) (Ω) 0.09

NF (dB) 1.98

CP1 (dBm) -23.6

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Calibration of Input matching

2.440 2.445 2.450 2.455 2.460 2.4652.435 2.470

-60

-40

-20

-80

0

freq, GHz

dB(S

(1,1

))

2.450G-28.59

m1

2.450000G-28.58573

m2

2.450000G-28.58573

m3

m1freq=dB(S(1,1))=-57.965Cs=1.505000E-12

2.450GHzm2freq=dB(S(1,1))=-40.773Cs=1.006667E-12

2.450GHzm3freq=dB(S(1,1))=-28.586Cs=3.000000E-12

2.450GHz

2.42 2.43 2.44 2.45 2.46 2.472.41 2.48

40

45

50

55

35

60

freq, GHz

real

(Zin

1)

2.450000G53.86025

m4

2.450000G53.86025

m5

m4freq=real(Zin1)=47.341Cs=1.000000E-14

2.450GHz

m5freq=real(Zin1)=53.860Cs=3.000000E-12

2.450GHz

• Cs is swept around 1500fF (nominal value ) : [10fF – 3000fF]

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Impact of input matching calibration on the other LNA performances at 2.45GHz

Parameter Variation range

S21 (dB) [20.21 , 20.74]

Im(Zin) (Ω) [-0.19 , -0.03]

S22 (dB) [-53.14 , -43.08]

Re (Zout) (Ω) [49.3 , 49.83]

Im (Zout) (Ω) [0.049 , 0.138]

NF (dB) [1.98 , 1.99]

CP1 (dBm) [-23.3 , -23.87]

Low variation of LNA gain, Noise Figure and linearity when calibrating the input impedance

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Technique of input matching and its center frequency calibration for an Inductively degenerated LNA

Calibration of input match center frequency

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Calibration of input match center frequency

2.2 2.3 2.4 2.5 2.6 2.7 2.82.1 2.9

-60

-40

-20

-80

0

freq, GHz

dB

(S(1

,1))

2.448G-64.93

m1

2.349G-21.79

m2

2.563G-6.086

m3

m1freq=dB(S(1,1))=-64.930Cg=3.132857E-13

2.448GHzm2freq=dB(S(1,1))=-21.789Cg=3.750000E-13

2.349GHzm3freq=dB(S(1,1))=-26.816Cg=2.670000E-13

2.563GHz

2.42 2.43 2.44 2.45 2.46 2.472.41 2.48

40

45

50

55

35

60

freq, GHz

real

(Zin

1)

2.450G50.09

m4

m4freq=real(Zin1)=50.095Cg=3.750000E-13

2.450GHz

Center frequency tuning band = 214MHz

It is clear that when tuning center frequency there is no impact on input matching

• Cg is swept in the range [267fF – 375fF]

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Parameter Variation range

S21 (dB) [20 , 20.5]

S22 (dB) [-48.42 , -31.29]

Real(Zout) (Ω) [47.77 , 50.14]

Imag(Zout) (Ω) [-2.16 , 1.45]

NF (dB) [1.77 , 2.41]

CP1 (dBm) [-23.15 , -23.62]

Impact of center frequency calibration on the other LNA performances at 2.45GHz

Gain and linearity are not affected by Noise figure varies a little but still lower than 3dB

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Conclusion and future works

• A technique is proposed for calibrating the input matching and central

frequency for an Inductively Degenerated Low Noise Amplifier operating at 2.45GHz.

• We studied the impact of each perfomance calibration on the others

performances of the LNA at 2.45GHz, good results are observed since

these calibrations have no significant effect on the other

characteristics of the LNA.

• In the future: we will investigate on some other calibration techniques

for the other LNA performances (Gain, Noise figure, linearity)

THANK YOU