A Fully Integrated MIMO Multiband

Direct Conversion CMOS Transceiver

for WLAN Applications (802.11n)

Reviewed by Yu-Shan Wang

Arya Behzad et al. (Broadcom Corporation)

IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 42, NO. 12,

DECEMBER 2007

Outline

• Introduction of 802.11n and MIMO

• Transceiver architecture

- TX,RX,PLL

• Calibration techniques

- LOFT, IQ mismatch

• Measurement Summary

• Conclusion

Comparison of WLAN standards

• IEEE 802.11n highlights:

– Spatial division multiplexing (SDM) through

the use of MIMO–OFDM

– Transmit beam forming

– Bandwidth expansion (40MHz)

– Advanced backend processing

802.11a 802.11b 802.11g 802.11n

Freq.

band(Hz)

5G 2.4G 2.4G 2.4G/5G

Data rate(bps) 6-54M 5.5-11M 1-54M >100M

Modulation OFDM CCK DSSS/CCK/O

FDM

OFDM

Why MIMO?

• Spatial multiplexing can increase the

channel capacity dramatically

• CSISO = BW log2(1 + SNR)

• CMIMO = min(n, m) BW log2(1 + SNR)

Transceiver

Receiver architecture

•Fully differential Direct conversion receiver

•HPVGA programmable gain of 0 to 30dB in 3dB steps

•4th order Butterworth LPF bandwidth 5,10,20MHz

• RX gain >100dB

•RX IIP3 of -12dBm @ high gain

•RX NF of 4dB @ maximum gain

Transmitter

•Direct conversion

•Driving 50 ohm load through a balun and internally matched to 100 ohm differential

•LOFT and IQ calibration

•OIP3 of +14dBm in the A-band while OIP3 of +16dBm in the G-band

•EVM <- 40dB for both bands

TX Mixer transconductor

PA

PLL

•Very low noise regulator

LO generation and distribution

•To avoid pulling effects : VCO operates at 2/3 the channel frequency for 11a

VCO operates at 3/4 the channel frequency for 11b/g

Calibration Techniquies

• LOFT @ TX

• IQ mismatch @ TX/RX

• LPF/HPF corner

• VCO

• Temperature sensor

Sources of LOFT in a direct-

conversion transmitter

• BB_LOFT: device offsets

• RF_LOFT: direct-coupling

Sources IQ imbalance in a direct-

conversion transmitter

•BB_IQ: Device mismatch,bias, mismatch

•RF_IQ: LO IQ inbalances and mixer IQ mismatch

Simplified block diagram of LOFT

and IQ imbalance estimation

circuitry

Gain control independent LOFT cancellation Algorithm

RX IQ calibration

Same core method:

image rejection is -35dBc

Same core method:

image rejection is -50dBc

Measurement results

Die

•Die area: 18mm2 ( compare to 11a: 12mm2)•Package: 165 ball fpBGA

Conclusion

• The highest performance, lowest power, smallest

area, multiband draft 802.11n transceiver published

to date has been implemented.

• 1.8V supply, 0.18um CMOS

• PHY rates > 270Mbps

• Effective throughput >190Mbps

• Can utilized in a multi-transceiver configuration to

build a larger MIMO system (4X4)

Questions?

Thank you