A Direct-Conversion CMOS Transceiver with ...

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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)