Post on 13-Jan-2016
description
transcript
All Rights Reserved © Alcatel-Lucent 2006, 2008
Enabling high efficiencies
Digital signal conditioning in modern RF transmitters
Thomas BOHN
June 2008
All Rights Reserved © Alcatel-Lucent 2006, 20082 | Enabling high efficiencies | June 2008
Agenda
1. Overview
2. Peak-to-Average-Power-Ratio (PAPR) Reduction
3. Power amplifier linearisation
4. Image suppression and DC-offset compensation
5. Conclusions
All Rights Reserved © Alcatel-Lucent 2006, 20083 | Enabling high efficiencies | June 2008
1 Overview
Architecture of a modern RF transmitter
All Rights Reserved © Alcatel-Lucent 2006, 20084 | Enabling high efficiencies | June 2008
Transmitter architecture
Digital-in analogue-out RF amplifier– Signal conditioning right in front of the analogue PA chain
Easiest (cheapest) possible analogue design Highest possible power efficiency
Clipping Predistortion
Digital-Module
D/A-conv.
Conversion-Module
Image- &Carrier-Suppr.
PA chain
PA-Module
Wide bandDown-conversion
A/D-conv. Time Delay
Compens.
Modulation &Wide bandUp-conversion
All Rights Reserved © Alcatel-Lucent 2006, 20085 | Enabling high efficiencies | June 2008
2 PAPR Reduction
All Rights Reserved © Alcatel-Lucent 2006, 20086 | Enabling high efficiencies | June 2008
PAPR ReductionWhat is PAPR reduction ? Clipping !
Reducing signal power peaks to a certain threshold– increasing the EVM
Power @ Soft Clipping Power @ Hard Clipping
All Rights Reserved © Alcatel-Lucent 2006, 20087 | Enabling high efficiencies | June 2008
PAPR Reduction Why do we perform PAPR reduction ?
PA has to be designedfor the signal peak driving into saturation
produces intermodulation
PA delivers an averageoutput power
Black: PAPR: 10.9 dB 43dBm (12% efficiency)
Blue: PAPR: 5.5 dB 45.2 dBm (16% efficiency)
Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes)
Ref 50.6 dBm Att 10 dB *
Offset 50.5 dB
AVG
A
LVL
Center 2.14 GHz Span 25.5 MHz2.55 MHz/
*
*
*1 RM
RBW 30 kHz
VBW 300 kHz
SWT 500 ms
3DB
*
*2 RM
VIEW
*
-50
-40
-30
-20
-10
0
10
20
30
40
50
SWP 3 of 3
CH PWR 45.19 dBm
ACP Low -45.90 dB
ACP Up -46.11 dB
ALT1 Low -58.45 dB
ALT1 Up -58.34 dB
Date: 9.JUN.2008 17:19:10
All Rights Reserved © Alcatel-Lucent 2006, 20088 | Enabling high efficiencies | June 2008
3 PA linearisation
Digital predistortion for higher efficiencies
All Rights Reserved © Alcatel-Lucent 2006, 20089 | Enabling high efficiencies | June 2008
PA linearisationHow to linearise a PA ? With (digital) predistortion !
Principle of PA linearisation:
Amplitude distortions can be compensated up to the PA’s saturation point
Phase distortion can be compensated for arbitrary input amplitudes
Phase
x in PD x
act
y des
y sat
y
x
y
x
All Rights Reserved © Alcatel-Lucent 2006, 200810 | Enabling high efficiencies | June 2008
PA linearisationDigital predistortion - the PA
Complex baseband model for the PA:
Quasi-static nonlinear model (static in the complex baseband) AM-AM and AM-PM distortions Complex gain model:
– x, y: Complex envelope of RF input and output signal
PA(|x|) Complex gain depending on the magnitude of the input signal
– G(|x|) Magnitude of the gain (|x|) Phase shift
– ai Complex coefficients
All Rights Reserved © Alcatel-Lucent 2006, 200811 | Enabling high efficiencies | June 2008
PA linearisationDigital predistortion - the linearisation
PA linearisation with inverse PA characteristic:
Linear PA transfer characteristics up to saturation point:
– x, y: Complex envelope of RF input and output signal Constant real gain
Linearised PA transfer characteristics up to saturation point:
– G(|x|) Magnitude of the gain (|x|) Phase shift
– ai Complex coefficients
All Rights Reserved © Alcatel-Lucent 2006, 200812 | Enabling high efficiencies | June 2008
PA linearisationDigital predistortion - the non-linearity (1)
The intervals over the input signal power:
Pout
PA transfer characteristic just for illustration The “r” depicts the power of the current input sample in the 2nd interval
r1 r r2 r3 (max.) PIN
All Rights Reserved © Alcatel-Lucent 2006, 200813 | Enabling high efficiencies | June 2008
PA linearisationDigital predistortion - the non-linearity (2)
In the interval : 1 ii rrr
)()()()()( 32322222121222 rarararar iiiiiiiiPD
4
27
4
27
s
s
-
s
s
0 2
10
1
10
10
3
1
0
11
All Rights Reserved © Alcatel-Lucent 2006, 200814 | Enabling high efficiencies | June 2008
PA linearisationDigital predistortion - the non-linearity (3)
Block diagram of the PIPOP:
PD calculation foreach input sample
Predistortion ofeach input sample
Issues to ease theimplementation: f(x) (= 1 ?)
Base functionsgranularity
Interval widths(equal ?)
Input signalx
Output signaly
Coefficient input
| . |2
f(x)
Delay
Determine
interval no. addresses
offsetCalc.
Calc. coeff.
Function
Function
Function
Coefficient
storage
0
Function
1
2
3
i
r
s
Determineinterval width
a a2i 2i+3
All Rights Reserved © Alcatel-Lucent 2006, 200815 | Enabling high efficiencies | June 2008
PA linearisationDigital predistortion - the adaptation
Coefficient update formula:
For each of the four ( 0 k 3) coefficients within one interval
c - coefficient - step width of the algorithm - hermite base function y’* - complex conjugated PD output signal (y’ is the delayed y) e - error (y’ - w) - PD gain
)()()(')|)((|)()1( *2 nnenynxmcmc kkkk
All Rights Reserved © Alcatel-Lucent 2006, 200816 | Enabling high efficiencies | June 2008
PA linearisationDigital predistortion - the system
Schematic view:
PA
MEM MLN
MLN(1)coeffs
I/Q (out_data)
int_delay
TD
OUT
Y_ IN
(FB)
Base functionsI/Q (in_data)
Z (OUTPUT)
FB gain
fb_factor
INPDtap delay
PD Error
PDtap delay
MLN(1)Adaptation
Base functions
Error
IN (I/Q)
MLN(2)Adaptation
Base functions
Error
IN (I/Q)
MLN(2)coeffs
X (INPUT)
Y
Integer delay
Data PD
BFMLNMLN(1) +MLN(2)
MLN(3)
MLN(4)
PDtap delay
PD Gain ()
All Rights Reserved © Alcatel-Lucent 2006, 200817 | Enabling high efficiencies | June 2008
PA linearisationEfficiency and spectral distortions in case of 1 carrier UMTS (1)
Blue: 46.0 dBm 18.2% efficiency out of spec
Black: 43.0 dBm 11.9% efficiency in spec
Green: 40.6 dBm 8.35% efficiency in spec
Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR)
Ref 50.6 dBm Att 10 dB *
Offset 50.5 dB
A
LVL
Center 2.14 GHz Span 25.5 MHz2.55 MHz/
*
*
RBW 30 kHz
VBW 300 kHz
SWT 500 ms
*3 RM
VIEW
3DB
*
*
*2 RM
VIEW
*1 RM
VIEW
-50
-40
-30
-20
-10
0
10
20
30
40
50
SWP 3 of 3
CH PWR 45.87 dBm
ACP Low -41.57 dB
ACP Up -41.59 dB
ALT1 Low -56.92 dB
ALT1 Up -56.18 dB
Date: 3.JUN.2008 17:40:01
All Rights Reserved © Alcatel-Lucent 2006, 200818 | Enabling high efficiencies | June 2008
PA linearisation Efficiency and spectral distortions in case of 1 carrier UMTS (2)
Green: 46.0 dBm 18.2% efficiency out of spec
Blue: 46.0 dBm memory-less PD in spec with 5dB margin
Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR)
Ref 50.6 dBm Att 10 dB *
Offset 50.5 dB
A
LVL
Center 2.14 GHz Span 25.5 MHz2.55 MHz/
*
*
RBW 30 kHz
VBW 300 kHz
SWT 500 ms
*3 RM
VIEW
3DB
*
*
*1 RM
VIEW
-50
-40
-30
-20
-10
0
10
20
30
40
50
SWP 3 of 3
CH PWR 45.95 dBm
ACP Low -54.01 dB
ACP Up -53.82 dB
ALT1 Low -63.61 dB
ALT1 Up -63.23 dB
Date: 3.JUN.2008 18:01:29
All Rights Reserved © Alcatel-Lucent 2006, 200819 | Enabling high efficiencies | June 2008
PA linearisation Efficiency and spectral distortions in case of 1 carrier UMTS (3)
Green: 47.0 dBm 20.4% efficiency out of spec
Blue: 47.0 dBm memory-less PD in spec
Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR)
Ref 50.6 dBm Att 10 dB *
Offset 50.5 dB
A
LVL
*
Center 2.14 GHz Span 25.5 MHz2.55 MHz/
*
*
RBW 30 kHz
VBW 300 kHz
SWT 500 ms
*
*2 RM
AVG
1 RM
AVG
3DB
*
*3 RM
VIEW
-50
-40
-30
-20
-10
0
10
20
30
40
50
SWP 3 of 3
CH PWR 46.88 dBm
ACP Low -45.02 dB
ACP Up -47.69 dB
ALT1 Low -53.14 dB
ALT1 Up -55.31 dB
Date: 3.JUN.2008 18:17:26
All Rights Reserved © Alcatel-Lucent 2006, 200820 | Enabling high efficiencies | June 2008
PA linearisation Efficiency and spectral distortions in case of 4 carrier UMTS (1)
Blue: 46.0 dBm 17.8% efficiency out of spec
Black: 31.7 dBm 1.2% efficiency out of spec
Green: 25.5 dBm 0.3% efficiency out of spec
Set-up: PA rated for 46.0 dBm; 4 x 3GPP test model 1 (64 codes, 5.5 dB PAPR)
Ref 50.6 dBm Att 10 dB *
Offset 50.5 dB
A
LVL
Center 2.14 GHz Span 50 MHz5 MHz/
*
*
3DB
RBW 30 kHz
VBW 300 kHz
SWT 160 ms*
*3 RM
VIEW
*2 RM
VIEW
*1 RM
VIEW
-50
-40
-30
-20
-10
0
10
20
30
40
50
SWP 3 of 3
CH1 39.81 dBm
CH2 39.94 dBm
CH3 39.97 dBm
CH4 40.10 dBm
Total 45.98 dBm
ACP Low -34.01 dB
ACP Up -34.05 dB
ALT1 Low -35.26 dB
ALT1 Up -34.97 dB
Date: 3.JUN.2008 17:49:55
All Rights Reserved © Alcatel-Lucent 2006, 200821 | Enabling high efficiencies | June 2008
PA linearisation Efficiency and spectral distortions in case of 4 carrier UMTS (2)
Green: 46.0 dBm 17.8% efficiency out of spec
Black memory-less PD out of spec
Green PD with memory effect
compensation in spec
Set-up: PA rated for 46.0 dBm; 4 x 3GPP test model 1 (64 codes, 5.5 dB PAPR)
Ref 50.6 dBm Att 10 dB *
Offset 50.5 dB
A
LVL
Center 2.14 GHz Span 50 MHz5 MHz/
*
*
RBW 30 kHz
VBW 300 kHz
SWT 160 ms
*3 RM
VIEW
3DB
*
*2 RM
VIEW
*1 RM
VIEW
-50
-40
-30
-20
-10
0
10
20
30
40
50
SWP 3 of 3
CH1 39.91 dBm
CH2 40.00 dBm
CH3 39.99 dBm
CH4 39.90 dBm
Total 45.97 dBm
ACP Low -50.46 dB
ACP Up -49.94 dB
ALT1 Low -51.82 dB
ALT1 Up -51.31 dB
Date: 3.JUN.2008 17:53:53
All Rights Reserved © Alcatel-Lucent 2006, 200822 | Enabling high efficiencies | June 2008
4 Image suppressionand DC-offset compensation
All Rights Reserved © Alcatel-Lucent 2006, 200823 | Enabling high efficiencies | June 2008
Image suppression and DC-offset compensation Zero-IF transmitter and efficiency
Simple architecture with small amount of analogue components:– 1 analogue quadrature modulator (QM, also known as IQ modulator)
– 1 local oscillator (LO)
Half of the signal bandwith @ DACs, Performance of DACs is best around 0 Hz
No frequency selective filters
But: QM has imperfections resulting in DC feed trough and image
DCI
DCQ
r(t)
90°+p
k
QM Modulator
DAC
DAC
v
LO(t)
z(t)
I
Q
All Rights Reserved © Alcatel-Lucent 2006, 200824 | Enabling high efficiencies | June 2008
Image suppression and DC-offset compensation Spectral distortions in case of 1 carrier UMTS (1)
Green: 46.0 dBm 18.2% efficiency out of spec
– ACP both
– ALT low
Blue: memory-less PD out of spec
– DC @ ACP low
– Image @ ALT low
Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR) @ 5MHz
Ref 50.6 dBm Att 10 dB *
Offset 50.5 dB
A
LVL
*1 RM
AVG
Center 2.145 GHz Span 25.5 MHz2.55 MHz/
*
*
3DB
RBW 30 kHz
VBW 300 kHz
SWT 500 ms*
*3 RM
VIEW
*2 RM
VIEW
-50
-40
-30
-20
-10
0
10
20
30
40
50
SWP 3 of 3
CH PWR 46.04 dBm
ACP Low -22.50 dB
ACP Up -46.01 dB
ALT1 Low -41.00 dB
ALT1 Up -52.56 dB
Date: 3.JUN.2008 18:05:57
All Rights Reserved © Alcatel-Lucent 2006, 200825 | Enabling high efficiencies | June 2008
Image suppression and DC-offset compensation Spectral distortions in case of 1 carrier UMTS (2)
Green : 46.0 dBm 18.2% efficiency out of spec
Black: memory-less PD out of spec
Blue: memory-less PD Image suppression and
DC-offset compensation in spec
Set-up: PA rated for 46.0 dBm; 3GPP test model 1 (16 codes, 5.5 dB PAPR) @5MHz
Ref 50.6 dBm Att 10 dB *
Offset 50.5 dB
A
LVL
Center 2.145 GHz Span 25.5 MHz2.55 MHz/
*
*
3DB
RBW 30 kHz
VBW 300 kHz
SWT 500 ms*
*3 RM
VIEW
*2 RM
VIEW
*1 RM
VIEW
-50
-40
-30
-20
-10
0
10
20
30
40
50
SWP 3 of 3
CH PWR 46.04 dBm
ACP Low -54.57 dB
ACP Up -53.87 dB
ALT1 Low -61.79 dB
ALT1 Up -62.63 dB
Date: 3.JUN.2008 18:07:59
All Rights Reserved © Alcatel-Lucent 2006, 200826 | Enabling high efficiencies | June 2008
5 Conclusion
All Rights Reserved © Alcatel-Lucent 2006, 200827 | Enabling high efficiencies | June 2008
Conclusion
We are working hard on increasing the energy efficiency of our products !
What about the energy efficiency of our workshop ?
All Rights Reserved © Alcatel-Lucent 2006, 200828 | Enabling high efficiencies | June 2008
www.alcatel-lucent.com