AbstractIn this paper, a number of tunable grounded
negative resistor circuits are presented. These new negative
resistors exhibit important features such as simplicity,
independent tunability and wide frequency range. One of the
introduced negative resistor circuits is simulated using TSMC 0.18m
process parameters and compared to a couple of other negative
resistors in the literature.
KeywordsMOS, resistance simulation, negative resistor, tunable
resistor, active resistor.
I. INTRODUCTION ECENTLY, there has been a growing interest in
the realization of active resistors, both positive and negative,
appropriate for on-chip fabrication. Not only positive-
valued tunable resistors but also negative-valued resistors are
increasingly being needed as a key element for the implementation
of filters, oscillators, amplifiers, mixers, artificial neural
networks and control systems [1-3].
Negative resistor implementations started with the discovery of
tunnel diode and continued with more and more improved circuits in
the literature [4-8]. Negative resistors were mostly preferred as
negative resistance loads (NRL) within these filter implementations
for the compensation of parasitic resistances. In the following
years, a number of floating and grounded resistance circuits have
been introduced and utilized in RF bandpass filter applications
[9-13]. In the last few years new techniques have been proposed for
the implementation of traditional cross-coupled transistor pairs
forming negative resistance [14-17]. In most of the reported
topologies in the literature coupling of negative resistance to the
main circuit appears as a problem, especially for floating negative
resistors. As the negative loads are designed within the circuits,
their bias currents and other parameters inevitably affect the main
circuit parameters and additional adjustment may be needed. A
number of examples concerning this issue can bee seen in
[8,9,13,14]. As a classical approach for implementing a negative
resistor, cross-coupled transistor pairs are arranged in grounded
topology in [14] and main drawback here is the reusage of the
current between negative resistance load and active inductor, which
affects the circuit parameters. Isolation between the negative
resistance load and the main circuit is important with the fact
that parasitic input capacitance and biasing issues directly change
the behavior of the main circuit. This need is fulfilled in [15] by
applying ac coupling for the separation of
Manuscript received May 5, 2011 A. Sunca is MS student at the
Dept. of Electrical & Electronics Engg
Bogazici University Istanbul/TURKEY (e-mail:
[email protected] ) O. Cicekoglu and G.Dundar are with the
Dept. of Electrical &
Electronics Engg Bogazici University Istanbul/TURKEY (e-mail:
[email protected], [email protected] )
the negative resistance load, which is a slight modification of
the negative resistor topology used in [14].
In this paper, we present a number of grounded negative resistor
circuits, all having different equations of resistance and these
circuits are to be ac coupled to the main circuit. Different from
the topology in [15], proposed negative resistors are easier to
bias and tune. In addition they have less number of transistors
including bias circuitry. Minimum dimensions can be used for the
transistors to keep the power consumption and input parasitic
capacitance low. One of the proposed negative resistor circuits is
examined and compared to that of a grounded negative resistor in
[8] and floating negative resistor in [7] by using the simulation
results obtained in [18]. In addition, a general comparison is made
regarding the usage of the proposed negative resistors among other
proposed negative resistor circuits in the literature.
II. CIRCUIT PRINCIPLE Negative resistors are well-investigated
in the aspects of
large and small signal characteristics including noise,
stability and bandwidth by [18]. Although negative resistors are
potentially unstable, their usage for compensation of parasitic
resistances makes them stable in higher level circuits.
Twelve negative resistance simulators are shown in Table III.
Each pair of them realizes the same input resistance as shown in
the table. Note that they are topologically related in pairs.
The gate-source capacitance of the MOS transistors may introduce
additional poles and zeros to the input impedance function that may
deteriorate the functionality of the circuit. To illustrate this we
examined the negative resistance simulator (b) in Table III
considering the gate-source capacitances and drain-source
conductances as a source of the non-ideality effect. The circuit is
repeated in Fig.1 for convenience. Its non-ideal input impedance is
given as:
( )( ) ( )
1 2 3 1 2 3 1 2 32
1 2 3 1 2 1 3 1 3 2 2 2 3 2 1 3 1 1 2 3 1
m m m o o oIN
m m m o o o o o m o o o o
g g g g g g s C C CZ
g g g g g g g g s g C g C g C g C g C sC C C+ + + + + + + +
=
+ + + + + + + + + + (1)
where gmi is the transconductance, Ci is the parasitic
gate-source capacitance of Mi and goi is the drain-source
conductance of Mi. Neglecting drain-source conductances, resistance
at low frequencies is given as:
2m1m
3m2m1meq gg
gggR ++= (2)
Note that the input impedance equation has a second order
denominator and it has a zero at:
321
3o2o1o3m2m1mz CCC
gggggg++
+++++= (3)
which implies one condition for desired operation as < z.
MOS Only Simulated Grounded Negative Resistors Abdullah Sunca,
Oguzhan Cicekoglu, and Gunhan Dundar
R
978-1-4577-1411-5/11/$26.00 2011 IEEE TSP 2011328
CIRCUITS Type1 Type2 EQUIVALENT RESISTANCE
(e) M2
M1
M3
M4
M2
M1
M3
M4
4m3m2m1m
3meq gggg
gR
+=
(f)
M2
M1
M3
M2
M3
M1
3m1m3m2m2m1m
2m1meq gggggg
ggR
++
+=
IV. CONCLUSIONS In this work a number of MOS negative resistor
circuits
are introduced. Large and small signal characteristics and
frequency response comparisons show that these new resistors can be
utilized in many applications requiring resistance compensation.
These resistor circuits are competitive among other implementations
in the literature due to the advantages in tunability, frequency
range, simplicity, capacitive loading and biasing. In addition,
these circuits can be accepted as multi-purpose negative resistor
blocks and they are potential candidates to be utilized in many
implementations in communication systems.
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