May 9, 2003 - T. T. Nguyen2,D. Yuan3, S. Wu, Y. C. Wong, V. Fong, A. Rofougaran. Broadcom Corporation, CA, USA. 1Now with Berkana Wireless, CA, USA.
A Direct-Conversion CMOS Transceiver with Automatic Frequency Control for IEEE 802.11a Wireless LAN
†
Berkeley Wireless Research Center May 9, 2003 A. Behzad, S. Anand, Z. M. Shi, L. Lin1, K. Carter, M. Kappes, E. Lin, T. T. Nguyen2, D. Yuan3, S. Wu, Y. C. Wong, V. Fong, A. Rofougaran
Broadcom Corporation, CA, USA 1 2
Now with Berkana Wireless, CA, USA
Now an Independent Consultant, CA, USA 3
†Paper 20.4, ISSCC 2003
Now with Qualcomm Inc, CA, USA
Outline •
IEEE 802.11a Introduction & RF Specifications
•
Transceiver Architecture
•
Automatic Carrier Frequency Control (AFC)
•
Measurement results
•
Conclusion
IEEE 802.11a Specifications • Data Rates and modulation types: Data Rate [Mbps]
60
CR=1/2 CR=3/4
50
54
CR=2/3
48 48
40
36
30
24
20
18 10 0
6
9 BPSK
12
QPSK
QAM-16
QAM-64
Modulation
• Multiple access:
FDM/CSMA-CA
• Min. Interframe Spacing:
16 us
• Subcarriers:
312.5 kHz spacing, 48 data, 4 pilots
• Signal bandwidth:
16.25 MHz (channel spacing = 20 MHz)
802.11a Bands & Max. Power
30
20
30 MHz
20
20
20 MHz
29dBm (800mW) 23dBm (200mW) 16dBm (40mW)
5150
5350 5725
5825 MHz
802.11a Minimum Requirements • Sensitivity:
Sensitivity [dBm]
-60 -65 -70 -75 -80 -85 0
10
20
30
40
50
60
Data Rate [Mbps]
• Tx. Error Vector Magnitude:
-25dB (QAM-64)
• Blocking:
-63dBm @ +/- 20 MHz
• Crystal Freq. Tolerance:
+/- 20 ppm (107 KHz Rx + 107 KHz Tx @ 5.35 GHz )
Outline •
IEEE 802.11 Introduction & RF Specifications
•
Transceiver Architecture
•
Automatic Frequency Control
•
Measurement results
•
Conclusion
Radio Architecture •
Goal: Lowest Cost, Highest Performance, Lowest Power Consumption Radio –
Direct Conversion Architecture
–
CMOS Implementation
–
Integrated PA
–
Take Advantage of Auto-Calibration Schemes
Implementation Challenges •
Direct Conversion: –
DC offsets
–
Flicker noise on receive path
–
Rx path and/or Tx path oscillations
–
Quadrature accuracy
–
LO pulling
–
LO feedthrough
•
Integrated PA –
•
High linearity requirements for PA
Auto-Calibration –
Automatic Carrier Frequency Control (AFC) Loop
Simplified Radio Architecture RX Baseband
Balun
JTAG
SW LO Generation
Optional BPF
PLL
XO AFC
Sensors out RSSI’s out RX_I out RX_Q out 4 wires JTAG Crystal Clock out AFC_I in AFC_Q in TX_I in
Balun
+
TX Baseband
TX_Q in RC & R calibration
Receiver Description • • • • • • • •
Direct conversion Full integration On-Chip LNA input matching High-gain, low-noise, high-linearity, gain controllable LNA/mixer 3 stages of high-pass VGA’s A 5th-order Chebychev LPF Dual RSSI’s System NF of 4dB and max gain of 93dB is achieved RSSIw out RSSIn out
RSSI RSSI
RF In (Diff)
HP
LPF
HP
HP
RX_I out
HP
LPF
HP
HP
RX_Q out
LNA
15/27
0/21
0/6
0/21
0/18 dB
Transmitter Description • • • • • • •
Direct conversion Full integration 3rd-order Butterworth LPF’s Baseband and RF VGA’s High-linearity, high-power integrated class AB power amplifier On-chip power amplifier output matching TX P-1dB of 19dBm and Psat of 23dBm are achieved
Pwr Detect RF Out (Diff)
LPF
TX_I in
LPF
TX_Q in
+
-9/26
-3/0
-27/0
0/6 dB
PLL Description • • •
Full Integration Integer-N PLL with programmable loop bandwidth “Fractional-VCO”† with fvco = 2/3 frf – – –
• •
Reduces pulling from high-power on-chip PA Reduces transmitter LO feed-through Reduces receiver DC offsets due to self-mixing
Automatic frequency control integrated into PLL PLL achieves PN of < -100dBc/Hz@30KHz offset with frf = 5.24 GHz
PLL
XO
1/2 3rd-LPF 3rd-LPF †
H. Darabi, et. al., ISSCC 2001
Crystal Clock out AFC_I in AFC_Q in
Outline •
IEEE 802.11 Introduction & RF Specifications
•
Transceiver Architecture
•
Automatic Frequency Control
•
Measurement results
•
Conclusion
The Need for Mixed Mode AFC -8.125
-.312
.312
8.125 MHz
Ideal
Subcarrier Index OFDM Subcarriers With Payloads Frequency offset
Subcarrier Index HPF
LPF
∆f
Standard requirement of 20PPM: 214KHz of frequency offset at 5.35GHz
AFC Mixed Mode Block Diagram TX RX
f LO _ TX
3 = ⋅ f vco 2
f LO _ RX
3 = ⋅ f vco + ∆f afc 2
∆f
20 MHz Xtal Rx LO = 5.25 + ∆f
Rx I Rx Q
ADC Frequency Estimation
PLL/VCO 3.5 GHz
∆f
1/2 1.75 GHz + ∆f
I AFC
Tx LO = 5.25 + (∆f = 0)
Q
LPF
DAC
LPF
DAC
Radio Chip
BB Chip
cos sin
LO_I
fVCO
Mix1
0.5fVCO_I Gain control fAFC_I ∆f
Mix5
Mix2
VGA1
VGA2
Gm1
Gm2
0.5fVCO
−∆f (image) 1.5fVCO LOFT +∆f (wanted) +2∆f (HD2) +3∆f (HD3)
Vdd
+3∆f (HD3)
−∆f (image) LOFT wanted +2∆f (HD2)
Block Diagram of LO Generation Mixers Vdd f LO_Q
fVCO
Mix6
f Mix3
0.5fVCO_Q Gain control fAFC_Q ∆f
Mix4
VGA3
VGA4
Gm3
Gm4
Simplified Schematic of LO Generation Mixers Vdd
LO_I+
LO_I-
VCO+ VCO-
Mix5
Mix1
Mix2
1/2VCO_I+
1/2VCO_Q+
1/2VCO_I-
1/2VCO_QAFCI+ AFCI-
Gm1+VGA1
Gm2+VGA2
AFCQ+ AFCQ-
Multi-section Class AB Offset-Gm of AFC mixer Gm_IVGA AFC_I-
AFC_I+ Gm_main
Gm_main [S]
Gm_I+
Gm3
Gm4 I_bias
Gm_overall [S]
Gm2
Gm_linearization [S]
Gm1
2.2m
Construction of Linearized Transconductance Gm_main
700µS
1.9m 1.9m
Gm3 Gm2
Gm4 Gm1
0.3m 6.97m
Gm_out
38µS
6.91m -400m
-200 m
0 Vin [V]
200m
400m
Chip Level Auto-Calibration •
VCO tuning
•
AFC
•
AFC self-calibration
•
R-Calibration on bandgap blocks
•
RC time constant calibration
•
Integrated power detector
•
Integrated temperature sensor
•
Transmit LO feedthrough cancellation
Outline •
IEEE 802.11 Introduction & RF Specifications
•
Transceiver Architecture
•
Automatic Frequency Control
•
Measurement results
•
Conclusion
Rx System NF and Sensitivity -60
100
12
Gain [dB]
-65
92
8
NF [dB]
6
88 84
4
Rx Sensitivity [dBm]
96
10
-70
8.9dB (σ = 0.4dB)
Spec
-75 -80 -85 -90
11.7dB
Measurement
(σ = 0.3dB)
-95
80
2 0.1
1 BB Frequency [MHz]
10
-100 0
20
40
Data Rate [Mbps]
60
AFC Performance AFC Disabled
AFC Enabled
A: Ch1 Spectrum
A: Ch1 Spectrum
Span = 36MHz
60%
Span = 36MHz
A: Ch1 OFDM Err Vect Spectrum
60%
LinMag
LinMag
6%/div
6%/div
0%
0% Start: -26 carrier
index
Stop: +26 carrier
A: Ch1 OFDM Err Vect Spectrum
Start: -26 carrier
index
Stop: +26 carrier
Multipath: 200ns, -2dB, 180deg; Frequency Offset: 200kHz
AFC Performance AFC Disabled
AFC Enabled A: Ch1 OFDM Meas
A: Ch1 OFDM Meas
RX EVM: -24.3dB
RX EVM: -28.4dB
Rx EVM Improved by 4.1dB
Measured Transmit Output Power Average OFDM Output Power [dBm]
24
saturated power limited
22
EVM limited
20
spectral mask limited
18 16 14 12 10 0
10
20
30 Data Rate [Mbps]
40
50
60
Measured TX Power Spectrum Ref Lvl 10 dBm
RBW 100 kHz VBW 30 kHz SWT 84 ms
RF Att 20dB Unit
Ref Lvl 10 dBm
dBm
10
10
0
0
-10
-10
-20
-20
-30
-30
-40
-40
-50
-50
-60
-60
-70
-70
-80
-80
-90 Center 5.28 GHz
10 MHz/
Span 100 MHz
12.8dBm, 54Mbps, QAM64 (EVM Limited)
RBW 100 kHz VBW 30 kHz SWT 84 ms
RF Att 20dB Unit
dBm
-90 Center 5.28 GHz
10 MHz/
Span 100 MHz
18.7dBm, 36Mbps, QAM16 (Spectral Mask Limited)
Measured TX Constellation Diagram EVM = -33dB Po = +6dBm 64-QAM 54 Mbps
Measured TX EVM Histogram
EVM = -33dB Po = +6dBm 64-QAM 54 Mbps
Measured Phase Noise
Target Specifications
10M
100M
Summary of Transceiver Performance Frequency Band RX NF RX Sensitivity (6Mbps) RX Sensitivity (54Mbps) RX IIP3 RX IIP2 RX Gain Range TX Power Range TX Psat TX P-1dB Vdd Vdd_PA Phase Noise @ 30KHz RX Power Consumption TX Power Consumption ESD Technology Die Size
Measured (this paper) 5.15 – 5.35 4 -93.7 ± 0.9 -73.9 ± 1.2 -4.8 > 30 15 to 93 -30 to +18.7 +23 +19 1.8 3.3 -100 150 380 (15dBm OFDM output) > ±2.5 on all pins 0.18um 1P5M CMOS 11.7 (including padring)
Unit GHz dB dBm dBm dBm dBm dB dBm dBm dBm V V dBc/Hz mW mW KV 2
mm
Die Microphotograph of Transceiver
RX
PLL/AFC
TX
Conclusion • Highest Performance, Highest Integration, Smallest Size, Lowest Power Consumption IEEE 802.11a Transceiver Reported to Date – High Performance • 4dB Rx chain noise figure • 23dBm Tx Psat with integrated PA • Excellent performance in the presence of real-world impairments – Low Cost • Fully integrated • Direct conversion – Low Power • 150mW Rx • 380mW Tx (transmitting 15dBm OFDM signal) – Various integrated self contained or system level calibration capabilities • High yield and tight tolerances
Acknowledgements The authors acknowledge the contribution of the following Broadcom Divisions: System Engineering (Sunnyvale, CA) CAD Support (Irvine, CA) RF Engineering (El Segundo, CA) Operations and Test Engineering (Irvine, CA)
In particular the contributions of the following individuals are greatly appreciated: B. Yeung, S. Tian, Terje Gloerstad, D. Yang, J. Castaneda J. Trachewsky, C. Hansen, T. Moorti, R. Gaikwad T. Kwan, A. Woo, L. Burns T. V. Nguyen, M. Chok, P. Wong, A. Ito, B. Bacher, J. To A. Niknejad (U.C. Berkeley)
