Hooman Darabi

1
Integration of RF Front-End on SoC
Hooman Darabi
Broadcom Corporation Irvine, CA
2
GSM Out-of-Band Blocking Issue
GSM out-of-band blocker profile
0dBm
-12dBm
-23dBm
-99dBm
PCS Band
Frequency, MHz
1990
2010
2070
1930
1910
1830

• Existing receivers use external SAW filter at the
  input to attenuate large out-of-band blockers
• The filter costs, and degrades sensitivity

3
Example of Current 2/2.5G Phones
PA
TX_HB
TX_LB
RX_1900
2G SoC
TR Switch
RX_1800
RX_900
RX_850
RX SAW
4
Problem of Full-Duplex Systems
TX Leakage
Large Blocker
RX Desired
Duplexer
RF IC
5
Example of Current 3G Phones
2G TX
3G TX
TR Switch
3G RF IC
3G BB
3G RX
2G RX
6
Next Generation 3G Phones
2G TX
3G TX
3G SoC
TR Switch
2/3G RX
2G RX
7
Future 3G Phones
2G TX
3G TX
3G SoC
TR Switch
2/3G RX
2G RX
8
Feed-Forward Blocker Cancellation
Blocker
Desired
LNA
Desired Band
Notch Filter
1.96G

• Similar to the SAW filter, the RF notch can not
  be implemented on chip

9
Concept of Receiver Translational Loop
LNA Frequency Response
Blocker
Desired
f3dB
fLO
Zero or Low IF
IN
RF Notch
RX Translational Loop
fLO
HPF
LO
f3dB
0
0
HPF Response
10
Blocker Filtering Architecture
RX IN
LNA
Filter Enable
Power Detector
LOQ
HPF
Zero or Low IF
h(t)
HPF
LOI
H(t) h(t) Cos(wLOt)

• Filtering path is an LTI system

11
Die Microphotograph
12
Amplifier Measured Frequency Response
20
10
Gain, dB
Simulated
0
w/o Filtering
-10
w/ Filtering
1.6
1.8
2
2.2
2.4
Frequency, GHz
13
Amplifier Measured Gain Over Frequency
20
1930M
1990M
10
Gain, dB
0
-10
1.6
1.8
2
2.2
2.4
Frequency, GHz
14
LNA Measured Gain with Blocker at Input
22
21
Gain, dB
20
19
Blocker at 1.88GHz Desired at 1.96GHz
18
-10
-6
-4
-2
0
-8
Blocker Power, dBm
15
TX Leakage Cancellation in 3G RX

• A blocker at fRX-DTX-RX/2, -30dBm leads to IIP3
  -1dBm

-30dBm
-25dBm
fTX
fRX
fTX
TX

• Linearize the RX Challenging and power consuming
• Use a notch similar to GSM RX
• Notch easier to implement than GSM, as TX leak is
  weak

16
3G TX SAW Removal

• In order not to affect RX sensitivity
  considerably, PN at DTX-RX of -160dBc/Hz needed

fTX
fRX
fTX
fRX

• Design the TX to meet the PN Very power
  consuming
• Use an integrated notch at TX output

17
Architecture of 3G TX with Notch Filtering
50W
New output impedance
fRX
fTX
PA Driver
PA
I

TX LO
Q
io
50 W
TX-to-RX Leakage
fRX
fTX
LPF
On-chip
Duplexer
I
RX LO
Q
18
Up-Conversion Mixer PA Driver Circuits
VDD
Cap Array
Cap Array
Bias
BBIQ
LPF Output, IQ
I
Q
I
Q
TX LO
RX LO
19
Die Microphotograph
20
Measured TX Transfer Function
15
w/o filtering
10
TX Gain, dB
5
w/ filtering
0
1.89
1.93
1.97
Frequency, GHz
21
Measured Receive-band Noise
TX at 1.85GHz
-152
Simulated
-154
Output Noise, dBc/Hz
-156
-158
Measured
-160
1.91
1.93
1.92
1.94
Frequency, GHz
22
TX Measured Output Spectrum
-10
3.3dBm Output
-20
-30
-40
Output Power, dBc/30kHz
-50
-60
-70
-80
Center 1.85GHz, Span 25MHz
23
TX Filtering Summary of Performance
24
Conclusions

• Current cellular systems use many external
  components for filtering and power amplification
• Feed-forward blocker cancellation in the LNA
  creates a notch in 2/3G receivers
• Eliminates the need for a front-end RX SAW filter
• RF filtering performed efficiently when
  translated to IF
• Feedback based notch enables low-power SAW-less
  3G TX
• Future cellular RF ICs with RF filters and PAs
  integrated are inevitable and imminent

25
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