class-s power ampliﬁer concept for mobile … power ampliﬁer concept for mobile communications...

Class-S Power Amplifier Concept for MobileCommunications in Rural Areas with Concurrent

Transmission at 450 MHz and 900 MHz

Martin Schmidt, Johannes Digel, Manfred Berroth

Institute of Electrical and Optical Communications Engineering

University of Stuttgart

Stuttgart, Germany

University of StuttgartInstitute of Electrical and Optical Communications EngineeringProf. Dr.-Ing. Manfred Berroth

1

2011 c© M. Schmidt/INT

Outline

MotivationChallenges for basestation suppliersClass-S principle

ArchitectureModulator lowpass prototypeMulti path transform5 path transform spectrum and SNR

Concurrent Transmission in both Frequency BandsOutput spectrumComparison of notches of both frequency bands

StabilityStability vs. input amplitudesExplanation of stability limit

Coding EfficiencyTotal output power and signal output powerSingle tone coding efficiency and combined coding efficiency

ConclusionUniversity of StuttgartInstitute of Electrical and Optical Communications EngineeringProf. Dr.-Ing. Manfred Berroth

2


Motivation


3


Motivation: Flexibility is Key

Challenges: High requirements . . .• Increasing number of standards,

(GSM, UMTS, CDMA2000, LTE, . . . )

• frequency bands(450 MHz, 900 MHz, 2.1 GHz)

• and use cases(coverage vs. data rate)

• in different markets.(Europe, North America, China, . . . )

Need for flexibility

. . . and high design efforts and costs.• Analog properties in advanced CMOS

technologies deteriorate

• Development in advanced CMOSnodes is expensive

and better designs /less design cycles


4


Motivation: Class-S Amplifier

HF

LO

090

Conventional Heterodyne Transmitter

BasebandProcessor


5



BasebandProcessor

Upsamplerand Mixer

BPDSMSwitching-mode PA

AnalogFilter

Class-S Transmitter

HF

LO

090


BasebandProcessor


5



BasebandProcessor

Upsamplerand Mixer


AnalogFilter

Class-S Transmitter

HF

LO

090


BasebandProcessor

Bandpass Delta Sigma Modulator


5



BasebandProcessor

Upsamplerand Mixer


AnalogFilter

Class-S Transmitter

HF

LO

090


BasebandProcessor


5



BasebandProcessor

Upsamplerand Mixer


AnalogFilter

Class-S Transmitter

The class-S amplifier concept is a “Software Defined Radio” solution.In general it• offers flexibility,

• low design effort,

• low power consumption and

• reduces number of analog components.


5



BasebandProcessor

Upsamplerand Mixer


AnalogFilter

Class-S Transmitter

• This presentation is about a special system for concurrent transmission inthe 450 MHz and the 900 MHz band.

• Main benefit: One solution for different use cases - coverage vs. data rate

• Only Bandpass Delta Sigma Modulator is treated here


5


Modulator Architecture


6


Modulator Lowpass Prototype

z−1

−1/16 −1/4

X Y

z−1

z−1

−1/2

−1/32


7


Lowpass Prototype Output Spectrum

0 0.2 0.4 0.6 0.8 1−140

−120

−100

−80

−60

−40

−20

0

Normalized Frequency / fs

Ou

tpu

t p

ow

er

[dB

]


8



z−1

−1/16 −1/4

X Y

z−1

z−1

−1/2

−1/32

transform z−1 → z−n


9



z− 1

−1/16 −1/4

X Y

z− 1

z− 1

−1/2

−1/32

z− n

−1/16 −1/4

X Y

z− n

z− n

−1/2

−1/32

transform z− 1 → z− n


9



z− n

−1/16 −1/4

X Y

z− n

z− n

−1/2

−1/32

X Y

LPDSM

LPDSM

LPDSM

1:n

DE

MU

X

n:1

MU

X

equivalent


9



0 0.2 0.4 0.6 0.8 1−140

−120

−100

−80

−60

−40

−20

0


Ou

tpu

t p

ow

er

[dB

]

0 0.2 0.4 0.6 0.8 1−140

−120

−100

−80

−60

−40

−20

0


Ou

tpu

t p

ow

er

[dB

]

0 0.2 0.4 0.6 0.8 1−140

−120

−100

−80

−60

−40

−20

0


Ou

tpu

t p

ow

er

[dB

]

0 0.2 0.4 0.6 0.8 1−140

−120

−100

−80

−60

−40

−20

0


Ou

tpu

t p

ow

er

[dB

]

n=2 n=3

n=4 n=5


10


Output Spectrum for Transform with n=5

0 0.5 1 1.5 2

−120

−100

−80

−60

−40

−20

0

Frequency [GHz]

Ou

tpu

t p

ow

er

[dB

]


11


Signal-to-Noise-Ratio of Single Sinusoids in Both Frequency Bands

0 10 20 30 40 50 6035

40

45

50

55

60

65

70

75

80

85

Bandwidth [MHz]

SN

R [dB

]

SNR @ 450 MHz

SNR @ 900 MHz


12


Concurrent Transmission in Frequency Bandsat 450 MHz and at 900 MHz


13


Output Spectrum for Concurrent Transmission

0 0.5 1 1.5 2

−120

−100

−80

−60

−40

−20

0

Frequency [GHz]

Ou

tpu

t p

ow

er

[dB

]


14


Zoom into Output Spectrum for Frequency Bands @1/5, 2/5fs

455.6 458.6 461.7 464.7 467.7 470.7 473.8 476.8 479.8 482.9 485.9 488.9

−100

−80

−60

−40

−20

0

Frequency 460MHz .. 467MHz−band [MHz]

928 931 934 937.1 940.1 943.1 946.2 949.2 952.2 955.2 958.3 961.3

−100

−80

−60

−40

−20

0

Frequency 935MHz .. 960MHz−band [MHz]

No

rma

lize

d O

utp

ut

Po

we

r [d

B]


15


Stability


16


Area of Stability: Definition

0 10 20 30 40 50 6035

40

45

50

55

60

65

70

75

80

85

Bandwidth [MHz]

SN

R [

dB

]

SNR @ Amplitudein

=3300• Modulator is considered

stable until SNR@bandwidth≈20 MHzdrops by 3dB frommaximum SNR at thispoint

• Here:

SNR(3400)+3 dB>SNR(3300)SNR(3500)+3 dB>SNR(3400)SNR(3600)+3 dB<SNR(3500)⇒ instable


17



0 10 20 30 40 50 6035

40

45

50

55

60

65

70

75

80

85

Bandwidth [MHz]

SN

R [

dB

]

SNR @ Amplitudein

=3300

SNR @ Amplitudein

=3400

• Modulator is consideredstable until SNR@bandwidth≈20 MHzdrops by 3dB frommaximum SNR at thispoint

• Here:SNR(3400)+3 dB>SNR(3300)

SNR(3500)+3 dB>SNR(3400)SNR(3600)+3 dB<SNR(3500)⇒ instable


17



0 10 20 30 40 50 6035

40

45

50

55

60

65

70

75

80

85

Bandwidth [MHz]

SN

R [

dB

]

SNR @ Amplitudein

=3300

SNR @ Amplitudein

=3400

SNR @ Amplitudein

=3500


• Here:SNR(3400)+3 dB>SNR(3300)SNR(3500)+3 dB>SNR(3400)

SNR(3600)+3 dB<SNR(3500)⇒ instable


17



0 10 20 30 40 50 6035

40

45

50

55

60

65

70

75

80

85

Bandwidth [MHz]

SN

R [

dB

]

SNR @ Amplitudein

=3300

SNR @ Amplitudein

=3400

SNR @ Amplitudein

=3500

SNR @ Amplitudein

=3600


• Here:SNR(3400)+3 dB>SNR(3300)SNR(3500)+3 dB>SNR(3400)SNR(3600)+3 dB<SNR(3500)⇒ instable


17


Area of Stability

0 500 1000 1500 2000 2500 3000 3500 40000

500

1000

1500

2000

2500

3000

3500

Amplitude @f=1/5fs

Am

plit

ud

e @

f=2

/5f s

Stability limit for signal @f=1/5fs

Stability limit for signal @f=2/5fs


18


Explanation of Stability Limit

0 2 4 6 8 10

−1

−0.5

0

0.5

1

1.5

2

2.5

3

Discrete Time

No

rma

lize

d A

mp

litu

de

sinusoid @f=1/5fs

sinusoid @f=2/5fs

combination of sinusoids


19


Explanation of Stability Limit

0 2 4 6 8 10

−1

−0.5

0

0.5

1

1.5

2

2.5

3

Discrete Time

No

rma

lize

d A

mp

litu

de

sinusoid @f=1/5fs

sinusoid @f=2/5fs

combination of sinusoids

Sampling instants ofone lowpass modulator

X Y

LPDSM

LPDSM

LPDSM

LPDSM

LPDSM

1:5

DE

MU

X

5:1

MU

X


19


Coding Efficiency


20


Total Output Power and Signal Power (Separate & Combined)

Power spectral density

SDT(k) =

∣∣∣∣ 1√NFFT

∑NFFT−1n=0 x(n)e

−j2πNFFT

nk∣∣∣∣


21



(0,0) (1,0) (0,1) (0,0)0

0.2

0.4

0.6

0.8

1

1.2

Normalized Amplitude (@f=1/5fs,@f=2/5f

s)

Norm

aliz

ed P

ow

er

Normalized total output power

Normalized signal output power

Normalized single tone output powerTotal output power

SDT(k) =

∣∣∣∣ 1√NFFT


−j2πNFFT

nk∣∣∣∣

Ptot =∑NFFT−1

n=0 x2(n) =∑NFFT−1

k=0 S2DT(k)


21



(0,0) (1,0) (0,1) (0,0)0

0.2

0.4

0.6

0.8

1

1.2


s)

Norm

aliz

ed P

ow

er

Normalized total output power

Normalized signal output power

Normalized single tone output powerSignal output power

SDT(k) =

∣∣∣∣ 1√NFFT


−j2πNFFT

nk∣∣∣∣

Ptot =∑NFFT−1

n=0 x2(n) =∑NFFT−1

k=0 S2DT(k)

SCT(k) = sinc(

kNFFT

)SDT(k)

Psig = S2CT(k1) + S2

CT(k2)


21


Coding Efficiency

(0,0) (1,0) (0,1) (0,0)0

5

10

15

20

25

30

35


s)

Codin

g E

ffic

iency [%

]

Combined output power

single tone output power Coding efficiency

SDT(k) =

∣∣∣∣ 1√NFFT


−j2πNFFT

nk∣∣∣∣

Ptot =∑NFFT−1

n=0 x2(n) =∑NFFT−1

k=0 S2DT(k)

SCT(k) = sinc(

kNFFT

)SDT(k)

Psig = S2CT(k1) + S2

CT(k2)

ηc =PsigPtot

=S2

CT(k1)+S2CT(k2)∑NFFT−1

n=0 x2(n)


22


Coding Efficiency vs. Input Amplitudes

00.2

0.40.6

0.81

0

0.5

10

10

20

30

40

NormalizedAmplitude @f=2/5f

s


s

Codin

g E

ffic

iency [%

]


23


Conclusion


24


Conclusion

Summary• Class-S transmitter offers high flexibility and low design effort

• For single tone transmission 60 dB SNR in 30 MHz bandwidth possible inboth frequency bands

• Concurrent transmission in the two important frequency bands 450 MHzand 900 MHz

• Stability depends on sum of input amplitudesdue to positive interference at one of the five low pass modulators

• Combined coding efficiency is better than coding efficiency for single toneexcitation

Outlook• Analysis of linearity

• Probability density function of output pulse widths (memory effect inpower amplifier)

• Average transition frequency (switching losses in power amplifier)


25


Conclusion

Summary• Class-S transmitter offers high flexibility and low design effort

• For single tone transmission 60 dB SNR in 30 MHz bandwidth possible inboth frequency bands

• Concurrent transmission in the two important frequency bands 450 MHzand 900 MHz

• Stability depends on sum of input amplitudesdue to positive interference at one of the five low pass modulators

• Combined coding efficiency is better than coding efficiency for single toneexcitation

Outlook• Analysis of linearity

• Probability density function of output pulse widths (memory effect inpower amplifier)

• Average transition frequency (switching losses in power amplifier)University of StuttgartInstitute of Electrical and Optical Communications EngineeringProf. Dr.-Ing. Manfred Berroth

25


Thank you for your attention


26


Backup


27


SNR @ 450 MHz 3d Plot vs. Input Amplitudes

00.2

0.40.6

0.81

0

0.5

130

35

40

45

50

55

60


s


s

SN

R [dB

]


28


SNR @ 900 MHz 3d Plot vs. Input Amplitudes

00.2

0.40.6

0.81

0

0.5

130

35

40

45

50

55

60


s


s

SN

R [dB

]


29


class-s power ampliﬁer concept for mobile … power ampliﬁer concept for mobile communications...

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