eecs 522 rf power amplifier with cartesian feedback
TRANSCRIPT
EECS 522 RF Power Amplifier with Cartesian Feedback
Alexandra Holbel, Fu‐Pang Hsu, and Chunyang ZhaiApril 18th, 2011
1
Outline• Motivation• Power Amplifier Design• Mixer Design• Cartesian Feedback• System Results
2
Motivation• RF transmitter for communication
– 2.4GHz
• Improve linearization with feedback
3
Power Amplifier Overview• Tradeoffs in PA design:
– Efficiency– Linearity
• Run PA close to saturation for efficiency, then use feedback to improve linearization
• RF PAs have a mixer to up convert the signal from baseband to RF
4
PA Schematic• Straightforward design
• Power efficient• Differential to reject RF coupling to power supplies
‐ vinVbias
Vbias Vbias
Vbias
+ vin
‐ vout+
Vbias
5
PA Simulation Results
Specification Results
PAE 48 %
1dB Compression (input referred)
‐1.89 dBm
Max Output Power 12 dBm
-30 -20 -10 0 10 20-20
-10
0
10
20
30
40PA 1dB Compression
Input Power (dBm)
Out
put P
ower
(dB
m)
1dB Compression Point
6
Mixer Schematic
IF+IF‐
LO+ LO+
LO‐RF+
RF‐
• Better isolation• LO and RF
rejection at IF output
• Higher linearity• Good
suppression of even order spurious product
• Less source voltage noise
7
Mixer Simulation Results
Specification Results
1dB Compression (input referred)
‐8.02 dBm
IIP3 1.57 dBm
RF to IF Isolation 77.63 dB
LO to IF Isolation 47.50 dB
LO to RF Isolation 95.88 dB
Conversion Gain 4.65 dB
Noise Figure 21.73 dB
Power Consumption 3.64 mW-40 -30 -20 -10 0 10
-40
-30
-20
-10
0
10
20
30Mixer 1dB Compression and IIP3
Input Power (dBm)
Out
put P
ower
(dB
m)
1dB Compression Point
IIP3
8
Cartesian Feedback• Improves distortion by increasing the linearity through feedback
• Uses two independent I and Q feedback loops• Robust for PVT variation
[Dawson] 9
H(s) Loop Filter• Slow rolloff
– 45 deg phase for stability
C
αC
α2Cα2R
αR
-40
-20
0
20
40
60
80
Mag
nitu
de (d
B)
103
104
105
106
107
108
109
1010
-90
-60
-30
Phas
e (d
eg)
Bode Diagram
Frequency (rad/sec)
sKsH )(
10
System Simulations
I
Q
I
Q
I
Q
Ideal Closed LoopOpen Loop
RF output
RF input
11
System Simulations
-30 -20 -10 0 100
5
10
15
20
25
30
35
401dB Compression Point for System
Input Power (dBm)
Out
put P
ower
(dB
m)
Red = Open LoopBlack = Closed Loop
1dB Compression Point
Specification Open Loop
Closed Loop
1dBCompression (input ref)
‐12 dBm ‐5 dBm
Max OutputPower
24 dBm 22 dBm
12
Results Summary
Specification [5] [6] Open Loop Closed Loop
1dB Compression (input referred)
‐10 dBm ‐31 dBm ‐12 dBm ‐5 dBm
Max Output Power 21.8 dBm 8 dBm 24 dBm 22 dBm
Area ‐ ‐ 1.15mm2 >1.15mm2
Power Amplifier
Upcon
versionMixer
Downcon
versionMixer
13
Future Works• H(s) implementation• Linearity of feedback mixer• Phase alignment design
14
Questions?
15
References[1] Chih‐Chun Tang; Wen Shih Lu; et al; “A 2.4 GHz CMOS
downconversion doubly balanced mixer with low supply voltage,” ISCAS, 2001.
[2] Palaskas, Y.; Taylor, S.S.; et al; “A 5 GHz class‐AB power amplifier in 90 nm CMOS with digitally‐assisted AM‐PM correction,” CICC, 2005.
[3] J.L. Dawson, Feedback Linearization of RF Power Amplifiers. United States: Kluwer Academic, 2004.
[4] J.K. Roberge, Operational Amplifiers: Theory and Practice. New York: Wiley, 1975.
[5] D. Chowdhury; et al, “A 2.4GHz mixed signal polar power amplifier with low‐power integrated filtering in 65nm CMOS,” ISSU, 2010.
[6] L. Perraud; et al, “A direct‐conversion CMOS transceiver for the 802.11a/b/g WLAN standard utilizing a Cartesian feedback transmitter,” JSSC, 2004.
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