338 IEEE JOURNAL OF SOLID-STATE CIRCUITS, VOL. 45, NO. 2, FEBRUARY 2010
A 250 MHz 14 dB-NF 73 dB-Gain 82 dB-DR Analog
Baseband Chain With Digital-Assisted DC-Offset
Calibration for Ultra-Wideband
Horng-Yuan Shih, Member, IEEE, Chien-Nan Kuo, Member, IEEE, Wei-Hsien Chen, Tzu-Yi Yang, and
Kai-Chenug Juang
Abstract—A 250 MHz analog baseband chain for Ultra-Wide-
band was implemented in a 1.2 V 0.13
m CMOS process. The chip
has an active area of 0.8 mm
2
. In the analog baseband, PGAs and
filters are carried out by current-mode amplifiers to achieve wide
bandwidth and wide dynamic range of gain, as well as low noise
and high linearity. Besides, a current-mode Sallen–Key low-pass
filter is adopted for effective rejection of out-of-band interferers. A
6th-order Chebyshev low-pass filter realized in
G
m
-C topology is
designed in the baseband chain for channel selection. Digitally-as-
sisted DC-offset calibration improves second-order distortion of
the entire chain. The design achieves a maximum gain of 73 dB and
a dynamic range of 82 dB. Measured noise figure is 14 dB, an IIP3
of
6 dBV, and IIP2 of 5 dBV at the maximum gain mode. The
analog baseband chain consumes 56.4 mA under supply of 1.2 V.
Index Terms—Analog filter, current-mode filter, current-mode
VGA, DC offset calibration, analog baseband, ultra wideband.
I. INTRODUCTION
E
NLARGING signal bandwidth is the most direct way
to increase the data rate in wireless transmission. For
the purpose, the spectrum from 3.1 GHz to 10.6 GHz was
approved by FCC for commercial applications of Ultra-Wide-
band (UWB) systems in 2002. Proposed by the WiMedia
alliance as Multi-Band (MB) OFDM UWB, the system realizes
a high date rate of 480 Mbits/s in short-range communication
as a wireless technique to replace cables. The spectrum is
partitioned into five band groups. Each band group consists
of three bands with a bandwidth of 500 MHz, which leads to
a large baseband bandwidth of 250 MHz in direct-conversion
receivers [1], [2]. Large signal bandwidth, however, leads to an
interference problem. It occurs that signals of other narrowband
communication systems, such as WiMax and WLAN, appear
as interferers to an UWB RF receiver, causing strict linearity
requirement [3].
An UWB RF receiver is composed of a broadband RF
front-end and a wideband analog baseband. While the RF
Manuscript received April 02, 2009; revised October 06, 2009. Current ver-
sion published February 05, 2010. This paper was approved by Associate Editor
Andreas Kaiser.
H.-Y. Shih and C.-N. Kuo are with the Department of Electronics Engi-
neering, National Chiao-Tung University, Hsinchu, Taiwan.
W.-H. Chen, T.-Y. Yang, and K.-C. Juang are with the SoC Technology
Center, Industrial Technology Research Institute (ITRI), Hsinchu, Taiwan.
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/JSSC.2009.2036320
front-end boosts up the signal level, interferers will also be
amplified. Typically the RF front-end carries out a low gain
level, as compared to that in a narrowband receiver, such that
the analog baseband can sustain those interferers. Consequently
the analog baseband shall provide sufficient gain with very
low input-referred noise to meet noise and gain requirements
of the entire receiver. It therefore includes programmable gain
amplifiers (PGAs) and filters. PGAs provide sufficient dynamic
range, while filters give channel selection. In general, it is
preferred to arrange in the order of PGAs, filters and PGAs
for the optimal performance regarding to noise and linearity
consideration of the overall analog baseband.
PGAs and filters are typically designed in voltage-mode
operational amplifier (op amp)-based circuits in narrowband
communication systems [4]. Those voltage amplifiers have
advantages of good gain accuracy, low process-voltage-tem-
perature (PVT) variation, and low power consumption. But
they have a very limited bandwidth at high closed-loop gains,
typically up to several tens of megahertz. Furthermore, in
advanced deep sub-micron processes, linearity performance
is greatly affected by rapid decrease of the maximum voltage
rating as devices are scaled down. Therefore, it is getting
harder to design high performance voltage-mode circuits. On
the other hand, current-mode amplifiers turn out more suitable
for realizing the UWB analog baseband. Low impedance at
current-mode circuit nodes easily leads to a wider operating
bandwidth [5], [6]. In addition, current-mode circuits feature
high linearity owing to small voltage swings and lower supply
voltage sensitivity than voltage-mode circuits. In 1968, a cur-
rent conveyer was proposed as the first building block intended
for current signal processing [7], then several proposals for a
CMOS current-mode OP-Amp have been published [8], [9].
In 1997, BJT-based current-mode variable gain amplifiers
(VGAs) are successfully realized by a trans-linear loop with at
least 250 MHz bandwidth, good blocking and inter-modulation
(IM) performance [10]. Later a 240 MHz low-pass-filter for
an UWB receiver has been successfully realized in the
-C
topology [11].
Another critical issue to baseband circuit design is DC-offset,
which might lead to second-order distortions arising from the
third-order nonlinearity in a balanced baseband circuit [12]. The
third-order inter-modulation between the input signal and the
DC-offset generates the second-order distortions. The propaga-
tion of the amplified second-order distortion from stage to stage
in the baseband chain not only degrades signal-to-noise ratio
0018-9200/$26.00 © 2010 IEEE
剩余12页未读，继续阅读
资源评论
