Download OTA Based Floating Inductance Simulator Lalit Soni NTPC

OTA Based Floating Inductance Simulator
Lalit Soni
Priyanka Soni
NTPC, Deesikha, Kaniha, Angul
Orissa, India
[email protected],[email protected]
Marudhar Engineering College, Raisar
Bikaner, Rajasthan, India
[email protected]
Abstract— A design of OTA based low pass filter is
introduced in this paper. The circuit implementation is
based on the floating inductor, floating resistor and
grounded resistor which uses CMOS based operational
transconductance amplifier (OTAs) as an active element.
This filter is synthesized from low-pass LC prototype
and designed using ladder structure. The simulation has
been carried out on Tanner EDA tool 13.0 on 0.5µm
technology.
Keywords— Floating inductor, grounded inductor, OTA,
Inductance simulator, low-pass LC prototype, low pass
filter
I.
we propose the 3-OTA based floating inductor. The
experimental results are shown in section IV and we
draw the conclusions in Section V.
II. OPERATIONAL TRANSCONDUCTANCE
AMPLIFIER
In the ideal OTA, the output current is a linear
function of the differential input voltage, calculated as
follows
Iout = (Vin+ − Vin− )g m
(1)
The transconductance gain (gm) of OTA can be
expressed as
INTRODUCTION
g m = √2βIB
The performance of filters designed by the use of
passive components degrades at audio frequencies and
the required resistances and inductances values
calculated from the mathematical expression are very
difficult to meet from the market. Filters are
indispensable parts of any communication systems.
There are various topologies to design a filter
depending upon the specifications and the application
in which the filter has to be employed like for low
frequency applications, active implementation is the
best suited. Keeping in view these applications, the
filter has been designed by replacing all the passive
components in a passive network with an active
device. OTA has been selected [1] as it suits us best
for the purpose and its CMOS implementation is
described. Electronically tuneable circuits attracted
considerable attention in the design of analog
integrated circuits because different values of
resistance, inductance or capacitance can be obtained
by the same device. The OTA provides a highly linear
electronic tunability for a wide range and powerful
ability to generate various circuits. Active inductors
are preferable over their passive counterpart as the
spiral wound passive inductor is bulky, expensive and
incapable of operating at the moderate frequency
range (KHz) without offering any signal loss. The
recent trends are to use the OTA for realizing the
floating inductor design [2] to use in place of the
passive ones. OTA can be used as the basic active
element for realizing the active inductors of both
topologies; grounded and floating [3]. In this paper, a
low pass filter has been taken up. This paper is
organized as follows. In Section II, we presents basic
operational transconductance amplifier. In section III,
(2)
Fig.1 Schematic of simple OTA
The CMOS implementation of the simple OTA is used
[4]. Note that β denotes the current factor [5]. It can be
seen that β can be given by μn Cox (W⁄L)n and
μp Cox (W⁄L)p for the NMOS differential pair based
OTA and the corresponding PMOS respectively.
Where µ is the mobility of the carrier, Cox is the gate
oxide capacitance per unit area, W is the effective
channel width, L is the effective channel length. From
Eq. (2), the gm is proportional to (IB)1/2.
III. CIRCUIT DESCRIPTION
The conventional 3-OTA based inductor [3] is shown
in Fig. 2. This circuit was implemented using OTA
CA3280 which was constructed on transistor level.
The proposed 3-OTA based inductor is shown in the
Fig. 3.
Fig. 4 RLC low pass filter topology
Fig. 2 Conventional 3-OTA based floating inductor
Fig. 5 Third-order low pass filter topology
Fig. 6 Fifth-order low pass filter topology
Fig. 3 Proposed 3-OTA based floating inductor
and L2(only for fifth order) is of the value 1.66mH
with IB=5 µA.
We infer that the inductance can be electronically
tuned by varying the external bias current IB.
IV. EXPERIMENTAL RESULTS
L12 =
C
gm 2
(3)
To demonstrate the electronically tunable properties of
the inductor, RLC low pass filter has been
implemented . A third-order and fifth order low pass
filter has been designed in this paper. An LC ladder
topology has been adopted, in which R1 and R2 are
OTA based floating and grounded resistor [6]
respectively while L1 and L2(only for fifth order) are
an active inductor. The capacitances C1,C2 and
C3(only for fifth order) are set to 1pF. The source
resistance R1=1/gm1 is chosen to be 1KΩ with IB
=8.33mA and load resistance R2= 1/gm2 is chosen to
be 28.86 KΩ with IB=10 µA. The simulated inductor
L1 and L2(only for fifth order) is of the value
0.83mH with IB=10 µA and the simulated inductor L1
Fig. 7(a) Response of third order RLC low pass filter for L=0.83mH
The proposed floating inductor and active low pass
filter was simulated using TSPICE. The circuit was
realized by CMOS implementation using 0.5 µm
technology process parameters. The power supplies
are selected as VDD = -VSS = 2.5V.
Fig. 7(a), 7(b), 8(a) and 8(b) shows the plots of
frequency response of RLC low pass filter. It can be
seen that the proposed floating inductor can be
employed instead of conventional if we are using
CMOS technology. In this work, all the three OTAs
for realizing the floating inductor are assumed to be
identical for resulting in the equality of their
corresponding parameters
V. CONCLUSION
Fig. 7(b) Response of third order RLC low pass filter for L=1.66
mH
A floating inductor using 3-OTAs with one grounded
capacitor has been proposed in this paper. The work
has been focused on 0.5 µm CMOS technology. The
inductance can be adjusted with external bias current
of OTAs. The proposed circuit has been found to
provide a sufficient accuracy and also promisingly
applicable to the RLC low pass filter. Simulation
results are showing the basic performance of the
floating inductor.
.
REFERENCES
[1].
[2].
[3].
[4].
[5].
[6].
Fig. 8(a) Response of fifth order RLC low pass filter for L=0.83mH
Fig. 8(b) Response of fifth order RLC low pass filter for L=1.66 mH
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