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Abstract— In this study, a new implementation of
reconfigurable analog baseband (ABB) low pass filter
employing cell-based variable transconductance amplifier
(cell-based VTA) is presented for multi-standard transceivers.
The configurability of the designed filter is supported by
activating different cells and changing biasing currents of each
cell. Multi-standard transceivers allow to process different
protocols in a single chip. These type transceivers need
reconfigurable analog elements. In this work reconfigurable
Analog Baseband low-pass filter is designed to support the
application of Bluetooth, CDMA2000, Wideband CDMA, and
IEEE 802.11a/b/g/n wireless LANs and 2G/3G/4G. The
designed filter operates between 20kHz-40MHz. The
minimum value of the designed filter’s third order intersection
point is 21.4dBm. The performance of the designed circuit is
tested with TSMC 0.18µm technology in CADENCE
environment.
Index Terms— Analog Baseband, Frequency agile filter, cell-
based variable gain amplifier, cell-based variable
transconductance amplifier, gm-C filter, Operational
Transconductance Amplifier
I. INTRODUCTION
Many kinds of communication such as Wi-Fi, Bluetooth,
Global Positioning Systems and so on require capability of
transceivers to these communication standards. Generally, the
commercial items must be compatible to the standards listed
above. For example, cell phone transceivers must process all
GSM, GPS, WCDMA, Wi-Fi (IEEE 802.11a/b/g/n), WiMAX,
Bluetooth, Zee Bee, Ultra Wideband (UWB) and so on for
more convenience. Such a transceiver named as multi standard
transceivers can process all standards with a single chip by
changing only software codes. This type chip production
decreases cost and area. Software Defined Radio (SDR)
transceivers provides these requirements [1].
The general structures of the Zero-IF transceiver and
receiver are given Fig. 1. To design multi standard transceiver,
LNA, local oscillators, mixers, filters and such architectures
1Bartin University, Department of Electrical and Electronics E ngineering,
Bartın, T urkey (e alaybeyoglu@bartin.e du.tr) Tel Nu mber:+90 378 510 1000-
1720 Fax Number: +90 (378) 501 1021
2Istanbul Technical University, Department of Electronics a nd
Communication Engineering, Istanbul, Turkey (ealaybeyoglu@itu.edu.tr,
kuntman@itu.edu.tr), Tel Number: +90-212-285 36 47 Fax Number: +90-
212-285 35 65
must be reconfigurable. For example, there exists a trade-off
in IF selection due to the restricted IF choice of 10.7 or 71
MHz for commercial filters, a super heterodyne RX for multi-
standard design normally constitutes a high cost for filtering at
different IFs [2]. New trend to design transceivers is Zero-IF
receiver which the incoming signal from the antenna is
transferred directly to baseband without IF and channel
selection. The input specifications for a flexible baseband low
pass filter intended for a multi-standard zero-IF receiver are
given in Table 1.
Furthermore, analog baseband (ABB) [3, 4] has two main
parts as low pass filter and programmable or variable gain
amplifier (VGA or PGA). Variable gain amplifier keeps
constant the output power for different input signals. Analog
signal controls VGAs, despite digital signal controls PGAs. As
an extended summary of applications, variable gain amplifiers
can be widely used in: WCDMA systems, Audio/Video analog
signal processing circuits, Portable communication drivers,
Hard disk drives, Medical equipment’s, hearing aids, Imaging
and wireless communications, Digital cable TV, satellite
television, Wireless communication systems, wireless LAN,
broadband residential communications, radio communicated
system. There are some different methods to design VGAs, for
example “cell-based” and “dB-linear” [5].
As for the ABB low pass filters, low pass filter must
provide different standard requirements to realize software
defined radio (SDR) transceivers. Because each standard has
different channel bandwidth [5-8]. For example, the cut-off
frequencies of some applications given as Bluetooth (650
kHz), CDMA2000 (700 kHz), Wideband CDMA (2.2 MHz),
IEEE 802.11a/g (10 MHz), IEEE 802.11b (12 MHz), IEEE
802.11n (20 MHz) wireless LANs, 2G (93kHz-340kHz ),
3G(HSPA SC/DC 1.92MHz-4.42MHz ) and 4G(LTE
1.4M~20MHz ).
The main problem to design reconfigurable ABB filter is
that “bring together the very low frequencies applications as
Bluetooth, 2G and etc. and the high frequencies applications
as 3G, 4G and etc.” in a single chip. This drawback increases
the core occupation of ABB filters. There are some designs in
the literature to collect all these standards in a single filter,
[10, 11].
In this work, a new OTA realization method as cell-based
variable transconductance amplifier and its voltage mode
reconfigurable ABB low pass filter is proposed for the
application of Bluetooth, CDMA2000, Wideband CDMA,
IEEE 802.11a/b/g/n wireless LANs and the designed filter is
also suitable for other wireless applications as 2G/3G/4G. The
A New Implementation of the Reconfigurable Analog
Baseband Low Pass Filter with Cell-Based Variable
Transconductance Amplifier
Ersin
Alaybeyoğlu
1
and
Hakan Kuntman
2
2
recommended OTA circuit is based on cell-based variable
transconductance amplifier (cell-based VTA). There are
different examples of the variable transconductance amplifier
are given those in [8, 9]. Cell-based VTA is inspired from cell-
based VGAs [5]. The recommended circuit is very suitable for
wide operation range, low power consumption and low
occupation area.
This paper is organized as follows. In the second section,
the CMOS realization of cell-based variable transconductance
amplifier is given. The cell-based design is explained in detail
in this section. In third section, the second order Butterworth
filter structure and its layout is given. Transient and AC
analysis of the ABB filter are done for all applications of
Bluetooth, CDMA2000, Wideband CDMA, IEEE
802.11a/b/g/n. The third order intercept point (IIP3), P1dB and
noise analysis are shown at the end of this section.
Additionally, the performance of the designed filter is justified
by comparing conventional designs.
Note that a preliminary version of this work entitled “A
New Method to Design Multi-Standard Analog Baseband
Low-Pass Filter” was presented in the 10th International
Conference on Electrical and Electronics Engineering
(ELECO), Bursa, Turkey [12]. This study is the extended
version of the above mentioned conference paper.
Table 1 Input specifications for a flexible baseband low-pass
filter intended for a multi-standard Zero-If receiver [4]
Standard BWtot
[MHz]
Min. Attenuation
[dB]
Vn,in
[µV
rms
]
IIP3
[dBm]
Bluetooth
1
30 @ 1.5MHz
96
-
183
17.3
UMTS TDD
1.28
63 @ 3.84MHz
52
-
104
18.4
UMTS FDD 3.84 58 @ 11.92MHz 51-106 20.42
DVB-H 7.6 49.8 @ 19.8MHz 62-127 17.9
WLAN
802.11a 16.66 49.8 @ 48.6MHz 53-105 21.5
WLAN
802.11b 33.2 49.8 @ 96.6MHz 75-149 21.5
Fig. 1 The general structure of the Zero-IF transceiver and
receiver
II. CELL-BASED VARIABLE TRANSCONDUCTANCE AMPLIFIER
CMOS IMPLEMENTATION
In this chapter, the basis of cell-based design for variable
transconductance amplifier is presented. The variability of
transconductance can be maximized with cell-based design of
variable transconductance amplifier. The proposed circuit can
allow more flexibility to design reconfigurable circuits. The
different examples of the variable transconductance amplifier
are given those [13, 14]. The design of cell-based variable
transconductance amplifier (VTA) is developed from the
CMOS implementation of the cell-based VGAs given in [5].
The recommended circuit is very suitable for wide operation
range, low power consumption and low occupation area in
chip. The realization method of the cell-based variable gain
amplifier is given Fig. 2.
Fig. 2 Overall design of “cell-based variable gain amplifier”
Very basic fully differential pairs consist each unit cell in
the structure of cell-based VGA. The different gain is obtained
by activating different cell digitally and by changing control
voltage. The gain of unique cell can be defined as “gm.ro”. In
this structure ro is relatively constant according to the change
of gm. gm is changed with Vbias and VCTRL voltages [4].
VTAs can be considered as current mode version of VGA.
This cell based design can be applicable to cell based VTA.
Actually, there are some differences between cell-based VGAs
and cell-based VTAs.
Firstly, OPAMP equation matrix gives Vo= A(Vin+ - Vin-)
and OTA equation matrix gives Io=gm(Vin+ - Vin-). Output
current of OTA can not drive another input of OTA. Because
of this reason, cell output currents of cell-based VTAs must
convert to the voltage. R1, R2, R3 and R4 (5kΩ) are used to
convert output current of each cells to the voltage. MOS
resistor can be applicable instead of these resistors. Second,
each cells in the cell-based VGAs can be randomly selected.
But, each cells in the cell-based VTA must be respectively
selected. As a result, the first cell is always activated.
The main problem of gm-C filters is linearity and noise. The
noise figure of the receiver is given by Friis in (1). NFTotal,
NFRF and NFBB are the noise figure of receiver, RF front-end,
and analog baseband. ABB includes low pass filter and
programmable gain amplifier. The input-referred noise of the
analog baseband is expressed in (2).
3
=
+
−
1
(1)
=
1
+
,
4
=
1
+
,
4
(2)
k is the Boltzmann coefficient, ,
is the input-referred
noise power specified for 1Hz bandwidth and is the
output impedance of the RF front-end. It can be easily seen
that the higher output impedance o f RF front end decreased
the baseband noise. The linearity performance of analog
baseband is given in (3).
1
,
=
1
,
+
,
(3)
,
, ,
and ,
are the input third-order
intercept point (IIP3) of the system, RF front-end, and analog
baseband sections. The CMOS structure of the symmetrical
operational transconductance amplifier with pMOS input
transistors is selected to overcome some linearity and noise
problems. Each cell of the designed cell-based variable
transconductance amplifier consists of symmetrical OTA. The
basic CMOS structure of the symmetrical OTA is given in Fig.
3. The CMOS implementation of the cell-based VTA is given
in Fig. 4. The size of the transistors is given in Table 2.
Fig. 3 Symmetrical operational transconductance amplifier
The frequency analysis of the transconductance with
activated single, double and triple cells is given Fig. 4. gm
changes between 1.23µS-549µS. This range optimized for the
selected applications of Bluetooth, CDMA2000, Wideband
CDMA, IEEE 802.11a/b/g/n wireless LANs and 2G/3G/4G.
The range of 1.23µS-549µS can be increased by adding extra
cells. These extra cells do not affect the operation frequency of
the filter because of the open loop structure of the cell based
VTA. R1, R2, R3 and R4 resistors are selected as 5kΩ. The
main reason for resistance connection is that “OTA output
impedance is not enough to drive MOS gate.” The minimum
value of the OTA’s output impedance is 75kΩ. MOS resistor
can be implemented instead of the classical resistors to
eliminate noise.
Also, one can claim that we can realize the ABB low pass
filter by using only one symmetric OTA.
First of all, the main purpose of multi-standard ABB low
pass filter is “put together the very low frequency operations
and high frequency operations 20kHz-40MHz. The single
symmetric OTA can not reach this frequency range. There are
lot of examples, which has different techniques to realize
multi-standard ABB low pass filter in literature. Second, the
number of transistors do not show the chip area. Some circuits
have 5 transistors and all transistors width can be 100µm.
Some circuits have 20 transistors and all transistors width can
be 1µm. The second type of circuit’s chip area is
approximately 25 times lower than the first type circuits. The
width of transistors given in Fig. 4 is short. In conclusion, the
total chip area of the designed circuit is not larger than the
other design given in [10, 11]. The frequency analysis of the
transconductance according to the activated cells is given in
Fig. 5.
Table 2 Transistor ratios of CMOS Realization
Transistors
First Cell
Second Cell
Third Cell
M
1
, M
2
, M
5
,
M6 360nm/360nm 3µm/360nm 9µm/360nm
M3, M4 1µm/360nm 1µm/360nm 3µm/360nm
M
7
, M
8
3µm/360nm
36µm/360nm
36µm/360nm
M
13,
M
14,
M15, M16 20µm/360nm 20µm/360nm 20µm/360nm
M
9,
M
10
,
M11, M12 360nm/360nm 3µm/360nm 9µm/360nm
S1
S1S2
S2
first cell second cell third cell
M1
M2
M3M4
M5
M6
M12
M7M8
M11
M10
M9
AVDD
AVSS
Vin-
Vin+
Ibias
Ron
M13
M15
M16
M14
M1
M2
M3M4
M5
M6
M12
M7M8
M10
M9
Vout-
Vout+
Ibias
Ron
M13
M15
M16
M14
M1
M2
M3M4
M5
M6
M12
M7M8
M10
M9
Ibias
Ron
M13
M15
M16
M14
AVDD AVDD
AVSS AVSS
R1R2R3R4
M11 M11
Iout+
Iout-
Fig. 4 CMOS implementation of cell-based VTA
4
Fig. 5 The frequency analysis of the transconductance
according to the activated cells
III. ABB LOW PASS FILTER IMPLEMENTATION WITH CELL-
BASED VTA
Second order low pass filter structure is given in Fig. 6. The
low-pass filter transfer function, center frequency and quality
factor are given in (4), (5) and (5), respectively. C1, C2 are
5pF.
The layout of the designed filter is given in Fig. 7. The core
of the filter occupies 150µm x 70µm (0.01mm2). Clean DRC
(Design Rule Checking), and ESD (Electrostatic Discharge)
protection are required for IC fabrication.
C1C2
gm1 gm2
-
+
-
+
Vin VLP
Fig. 6 Second order voltage mode OTA based low pass filter
AC and transient analyses for the application of Bluetooth,
CDMA2000, Wideband CDMA, and IEEE 802.11a/b/g/n
wireless LANs and 2G/3G/4G are realized to prove the
performance of the designed filter. Fig. 8 shows AC and
transient analyses for 2G. Analyses are performed for the
edges of the application of GSM (93kHz - 340kHz). It is
activated only one cell, to achieve GSM operating frequency.
2.63µS transconductance value is obtained with 3µA biasing
current. Eq. 5 shows that to reach very low frequency it is
desirable bigger capacitance (C1, C2) and lower
transconductance (gm1, gm 2). Bigger capacitances increases the
cost. At the same time, ABB low pass filter must assure high f-
3dB frequency. These situations have led us to adjust the
configurability by changing the transconductance. The cell-
based design is very appropriate for configurability of
transconductance.
The key analyses (third intersection point, transient
analysis, noise analysis and harmonic distortion according to
the input voltage swing) of the designed filter and comparison
table with conventional designs are given in the current study.
The performance of the designed filters is verified with TSMC
0.18µm in CADENCE.
1 2
2
1 2 1 1 1 2
m mLP
in m m m
g gV
V s C C sC g g g
(4)
1 2
0
1 2
m m
g g
C C
(5)
2 2
1 1
m
m
C g
QC g
(6)
Fig. 7 Layout of the overall circuit
Wide swing current source is used for biasing current of
each cell to improve head room. The current generator is in
good accordance of proportional to absolute temperature
(PTAT) and the complementary to the absolute temperature
(CTAT) to generate 20µA temperature independent reference
current. The switching is realized with standard CMOS switch
for different bias current from 1µA to 50µA. The switch of S 1
and S2 are implemented with complementary switches.
Fig. 9 shows AC and transient analyses for Bluetooth and
CDMA2000 applications. Bluetooth has 650kHz f-3dB
frequency, CDMA has 700kHz f-3dB frequency. Bluetooth and
CDMA2000 applications can be provided in the condition of
only one cell is active.
Fig. 10 shows AC and transient analyses for 3G. Analyses
are performed for the edges of the application of HSPA
SC/DC 1.92MHz/4.42MHz. Fig. 11 shows AC and transient
analyses for WCDMA and IEEE 802.11a/g applications.
WCDMA has 2.2MHz f-3dB frequency, IEEE 802.11a/g has
10MHz f-3dB frequency.
Fig. 12 shows AC and transient analyses for IEEE 802.11b
and IEEE 802.11n applications. IEEE 802.11b has 12MHz
cut-off frequency, IEEE 802.11n has 20kHz cut-off frequency.
Fig. 13 shows AC analysis for 4G. ABB filter must provide
1.4M~20MHz cut-off frequency for LTE.
The AC analysis for the overall circuit is given in Fig. 14.
Overall design operates between 93kHz-20MHz for the value
of gm 2.63µS-353µS. The operation range can increase for
50µA biasing current to 30MHz for 549µS transconductance.
But, 2.63µS-353µS values are enough for the selected
applications.
103104105106107
-1
0
1
2
3
4
5
6
7x 10-4
frequency (Hz)
gm (S)
gm changes between 1.23uS for single cell with 1uA biasing
to 549uS for triple cell with 50uA biasing
5
Fig. 8 AC and transient analyses for 2G
Fig. 9 AC and transient analyses for Bluetooth and
CDMA2000
Fig. 10 AC and transient analyses for 3G
Fig. 11 AC and transient analyses for WCDMA and IEEE
802.11a/g
Fig. 12 AC and transient analyses for IEEE 802.11b and
IEEE 802.11n
Fig. 13 AC analysis for 4G
1001051010
-150
-100
-50
0
50
35kHz f-3dB with unit cell at 1uA biasing
V (dB)
0 0.5 1
x 10-3
-0.4
-0.2
0
0.2
0.4
THD=%2.82 for 10kHz 300mV pp
V (V)
1001051010
-100
-50
0
50
V (dB)
frequency (Hz)
350kHz f-3dB with unit cell at 10uA biasi ng
0 2 4 6
x 10-5
-0.1
-0.05
0
0.05
0.1
0.15
V (V)
time (s)
THD=%1.42 for 200kHz 100mV pp
1001051010
-100
-50
0
50
V (dB)
650kHz f-3dB with unit cell at 35uA biasing
0 0.5 1 1.5 2
x 10-5
-0.1
-0.05
0
0.05
0.1
V (V)
THD=%1.44 for 500kHz 100mV pp
1001051010
-100
-50
0
50
frequency (Hz)
V (dB)
700kHz f-3dB with unit cell at 40uA biasing
0 0.5 1 1.5 2
x 10-5
-0.1
-0.05
0
0.05
0.1
time (s)
V (V)
THD=%2.41 for 500kHz 100mV pp
1001051010
-100
-80
-60
-40
-20
0
20
V (dB)
1.9MHz with double cell at 22uA biasi ng
01234
x 10-6
-0.05
0
0.05
0.1
V (V)
THD=%1.25 for 1.8MHz 100mV pp
1001051010
-100
-80
-60
-40
-20
0
20
frequency (Hz)
V (dB)
4.4MHz with double cell at 50uA biasi ng
01234
x 10-6
-0.1
-0.05
0
0.05
0.1
time (s)
V (V)
THD=%3 for 4MHz 100mV pp
1001051010
-100
-80
-60
-40
-20
0
20
V (dB)
2.2MHz with double cell at 25uA biasing
01234
x 10-6
-0.1
-0.05
0
0.05
0.1
V (V)
THD=%0.47 for 2MHz 100mV pp
1001051010
-100
-80
-60
-40
-20
0
20
frequency (Hz)
V (dB)
10MHz with triple cell at 28uA biasing
0 0.2 0.4 0.6 0.8 1
x 10
-6
-0.1
-0.05
0
0.05
0.1
time (s)
V (V)
THD=%1.47 for 10MHz 100mV pp
1001051010
-100
-50
0
50
V (dB)
12MHz f-3dB with triple c ell at 30uA biasing
0 0.5 1
x 10-6
-0.1
-0.05
0
0.05
0.1
V (V)
THD=%1.78 for 10MHz 100mV pp
1001051010
-100
-50
0
50
V (dB)
frequency (Hz)
20MHz f-3dB with triple c ell at 40uA biasing
0 0.5 1
x 10
-6
-0.2
-0.1
0
0.1
0.2
V (V)
time (s)
THD=%3.62 for 10MHz 100mV pp
104105106107108109
-80
-70
-60
-50
-40
-30
-20
-10
0
10
frequency (Hz)
V (dB)
LTE5 with double cell at 55uA biasing
LTE3 with double cell at 35uA biasing
LTE1.4 with double cell at 20uA biasing
LTE10 with triple cell at 28uA biasing
LTE15 with triple cell at 33uA biasing
LTE20 with triple cell at 40uA biasing
6
Fig. 14 The overall circuit’s AC analyses
Assuming that the receiver provides a NF of 9dB, an
overall IIP3 of 9dBm, and a gain requirement between 10 and
100dB, the range of all the requirements for the baseband
section is the result of an optimal tradeoff among gain, noise,
and linearity throughout the receiver blocks. By giving the
system analysis and the scenario simulated over the receiver,
the acceptable levels of the filter IIP3 for GSM/CDMA2000,
Wideband CDMA, and IEEE 802.11 /n mode are 19.2dBm,
21.1dBm, and 19.6dBm, respectively [15].
Input third-order intercept point is shown in Fig. 15. Two
tone test is applied all the applications of Bluetooth,
CDMA2000, Wideband CDMA, and IEEE 802.11a/b/g/n
wireless LANs and, also is suitable for other wireless
applications as 2G/3G/4G. The minimum value of the third
order intercept point is 21.4dBm for 2G.
Input referred noise for the application of IEEE 802.11
a/b/g/n and LTE10, LTE15, LTE20 are given in Fig. 16. Table
3 shows the performance of the designed filter. The given IIP3
values are in band. The frequency of the different tones to
perform IIP3 analysis are given in Fig. 15.
Fig. 15 The third-order input intercept point
Fig. 16 Input referred noise
Table 4 summarizes the performance comparison of the
designed ABB filter with reported those [4, 15-19]. When
considered power consumption and core occupation area, the
designed filter has very high performance than the others
given those [4, 15-19].
Table 3 The performance of the designed filter
Technology
0.18µm TSMC
Supply voltage
1.8V
Filter Type
Second order reconfigurable low pass filter (Butterworth Type)
Operation
range 35kHz - 20MHz*
Application
Bluetooth
CDMA2000
WCDMA
IEEE 802.11a/g
IEEE 802.11/b
IEEE 802.11/n
In
-
Band IIP3
25.8
dBm
25.8
dBm
31
.
6
dBm
31.6
dBm
31.6
dBm
35
.1dBm
Power
dissipation 0.9µW 0.58mW 1.73mW 3.47mW 3.7mW 4.89mW
Total
Harmonic
Distortion
1.44%
(@500kHz
100mV pp)
2.41%
(@500kHz
100mV pp)
0.47%
(@2MHz
100mV pp)
1.47%
(@10MHz
100mV pp)
1.78%
(@10MHz
100mV pp)
3.62%
(@10MHz
100mV pp)
Input referred
noise density 0.55µV/
√
0.48µV/
√
53nV/
√
2.4nV/
√
1.6nV/
√
0.6nV/
√
*The upper boundary of the operation frequency can
improve by adding extra cells.
1001021041061081010
-120
-100
-80
-60
-40
-20
0
20
frequency (Hz)
V (dB)
tuning range 35kHz-20MHz for the applications of
Bluetooth, cdma2000, Wideband CDMA,
IEEE 802.11a/b/g/n wireless LANs
and 2G/3G/4G
-20 -10 0 10 20 30
40
-100
-80
-60
-40
-20
0
20
40
input power (dBm)
normalized output power (dBm)
fundamental
IIP3=35.1 f1=10MHz, f2=12MHz (IEEE 802.11n and 4G)
IIP3=31.6 f1=1MHz, f2=1.2MHz (IEEE 802.11a/b/g,CDMA and 3G)
IIP3=25.8 f1=200kHz, f2=210kHz (Bluetooth and CDMA2000)
IIP3=21.4 f1=20kHz, f2=25kHz (2G-GSM)
108109
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
x 10
-10
frequency (Hz)
amplitude (V/sqrt(Hz))
LTE20, IEEE 802.11 n
LTE15
IEEE 802.11 b
LTE10, IEEE 802.11 a/g
7
Table 4 The comparison of designed filter with conventional designs
[16] [17] [18] [19] [4] [15] This Work
Technology
0.18µm
CMOS
0.18µm
CMOS
0.25µm
BiCMOS
0.13µm
CMOS
0.13µm
CMOS 0.18µm CMOS 0.18µm CMOS
Area
0.83mm
2
0.125mm
2
0.25mm
2
0.45mm
2
0.52mm
2
0.23mm
2
0.01mm
2
Type Gm-C Gm-C Gm-C
Active G
m
-
RC
Active
Gm-C Gm-C Cell-Based Gm-C
Supply
Voltage 1.8 1.8 2.5 1.2 1.2 1.2 1.8
Filter order
6
4
3
4
2
-
6
3
2
-
3dB
frequency
1.5MHz
-
12MHz
0.5MHz
-
12MHz
50kHz
-
2.2MHz
2.11MHz
-
11MHz
350kHz
-
23.5MHz
500kHz
-
23.5MHz 35kHz-20MHz
Tuning
ratio 8 24 40 5.5 67 40 50
App.
WCDMA/
IEEE
802.11a/b/g
Bluetooth
W-CDMA/
IEEE
802.11a/b/g
GSM
Bluetooth W-
CDMA/
CDMA2000
UMTS/
IEEE
802.11a/b/g
Software
Defined
Radio
Bluetooth W-
CDMA/
CDMA2000/
IEEE
802.11a/b/g/n
Bluetooth W
-
CDMA/
CDMA2000/
IEEE
802.11a/b/g/n/
2G/3G /4G
IIP3
Min
7.2dBm
9.4dBm
22dBm
21dBm
20dBm
19dBm
21
.
4
dBm
Mx 9.3dBm 11.1dBm 28dBm - 22.3dBm 35.1dBm
Pwr
Min
10mW
1.1mW
2.5mW
3.4mW
0.72mW
4.1mW
0.9µ
W
Mx
15mW
4.5mW
7.3mW
14.2mW
21.6mW
11.1mW
4
.8
9
mW
A figure of merit (FOM), which is independent to the
tuning ratio and die occupation area, is used to evaluate the
filter performance [4]. Small die occupation area is desired for
cost-effective design. As a result, the die occupation area is
important criteria for VLSI design. Because of that FOM is
plotted versus core occupation area of the designed circuits in
this work. Tuning ratio is also another important property for
ABB low pass filter. This ratio is displayed with H (highest
operating frequency) and L (lowest operating frequency) in
the FOM graphics.
=
(
)
/ (7)
Ptot is the total power dissipation of the filter, N is the
number of poles, fc is the cut off-frequency, SFDR(N)4/3 is the
normalized spurious-free dynamic range, with
SFDR=(IIP3/Pn)4/3 where Pn is the input-referred noise power.
Fig. 17 gives the comparison of FOM versus core occupation
area with similar publications. The capital letters of H and L
denote the highest and lowest frequency of the designed
filters.
The essential design criteria of the proposed Butterworth
low pass filter in this chapter is the operating range of the
applications of Bluetooth (650 kHz), CDMA2000 (700 kHz),
Wideband CDMA (2.2 MHz), IEEE 802.11a/g (10 MHz),
IEEE 802.11b (12 MHz), IEEE 802.11n (20 MHz) wireless
LANs, 2G ( 93kHz-340kHz ), 3G( HSPA SC/DC 1.92MHz-
4.42MHz ) and 4G( LTE 1.4M~20MHz ). Also, the acceptable
levels of the filter IIP3 for GSM/CDMA2000,Wideband
CDMA, and IEEE 802.11 mode are 19.2dBm, 21.1dBm, and
19.6dBm, respectively. Assuming that the receiver provides a
NF of 9dB, an overall IIP3 of 9dBm, and a gain requirement
between 10 and 100dB, the range of all the requirements for
the baseband section is the result of an optimal trade off
among gain, noise, and linearity throughout the receiver
blocks.
The designed voltage mode circuit ABB Low Pass Filter
With Cell-Based VTA given in this part supports the
aforementioned criteria. The current mode version of ABB
low pass filter designed with cell-based VTA are given those
[20, 21].
Fig. 17 FOM versus core occupation area
FOM [fJ]
8
ABB filter designed voltage mode approach in this work
has higher performance than the current mode version given
those [20, 21].
IV. CONCLUSION
In this work, a new implementation for analog baseband
low pass filter is proposed with OTA-C filters. Instead of
conventional operational transconductance amplifier’s CMOS
structure, cell-based variable transconductance amplifier is
used for CMOS implementation. The total input referred
integrated noise is calculated as 44µVrms between 1kHz-
40MHz. The total harmonic distortion at 2MHz for maximum
100mV peak value is 3.62%. The designed reconfigurable
filter supports the operating frequencies of the applications
{Bluetooth (650 kHz), CDMA2000 (700 kHz), Wideband
CDMA (2.2 MHz), IEEE 802.11a/g (10 MHz), IEEE 802.11b
(12 MHz), IEEE 802.11n (20 MHz) wireless LANs, 2G (
93kHz-340kHz ), 3G( HSPA SC/DC 1.92MHz-4.42MHz )
and 4G( LTE 1.4M~20MHz )}. The expected layout of the
designed filter is 0.02mm2. The designed second order filter
can easily improve for sixth order filter implementation. The
simulations are realized with TSMC 0.18µm CMOS
technologies.
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