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2017 Devices for Integrated Circuit (DevIC), 23-24 March, 2017, Kalyani, India
Low Power Design of Bulk Driven Operational
Transconductance Amplifier
Priti Gupta1, Suman Lata Tripathi2
ME Scholar, NITTTR, Chandigarh
Associate Professor, Lovely Professional University, Jalandhar
An operational transconductance-amplifier
(OTA) is basically designed for low voltage and low power
applications. Bulk driven technique is applied at the input
of the proposed OTA that allows the OTA to operate at the
minimum supply voltage. Bulk driven transistor removes
the threshold voltage limit of the transistor. The proposed
technique provides OTA with the rail-to-rail input range
with minimum supply voltage. In this paper, the bulk
driven technique is used to provide low power consumption
in the operational transconductance amplifier with
improvement in the transconductance of the amplifier. The
CMOS technology 45nm is used for the designing of the
proposed OTA circuit. Measurement results indicate that
the proposed OTA circuit operated with 0.7 V supply
voltage requires the 60.15% of lower power consumption
compared to the basic OTA circuit with slightly affecting
the other parameters such as transconductance, leakage
current, noise and leakage power.
Keyword: Moore’s Law, CMOS technology, Bulk driven
The Operational transconductance amplifier [1] is the
favorable active building block of analog circuits and
system. The Operational Transconductance amplifier
(OTA) is an amplifier (OTA) is an amplifier whose
differential input voltage produces an output current. It
is a voltage controlled current source (VCCS). The OTA
is like to a standard operational amplifier in that it has
comparatively high impedance differential input stage
and that it can be used with negative feedback. Reducing
[2-5], power consumption in portable applications has
made lower supply voltages increasingly common in
systems with large digital content. Fast [6], high-gain,
Operational Transconductance Amplifier (OTAs) are an
integral part of switched-capacitor (SC) circuits. It is a
voltage controlled current source that takes the
difference of the two voltages as the input for the current
conversion. There is an additional input for a current to
control the amplifiers transconductance. OTAs, are
useful analog building blocks that allow the
amplification and filtering of signals with lower power
consumption [7]. The Symbol of the OTA is shown in
Figure 1 Schematic Symbol for OTA
Iabc input bias current is used to control the
transconductance of the amplifier. Iabc is called amplifier
bias current of the amplifier. Iabc is directly proportional
to the amplifier's transconductance. This feature is useful
for the electronic control of amplifier gain. Previously
the OTA circuit does not use Ibias terminal and diodes as
shown in Figure 1. Later According to the requirement
these terms are included. The first terminal, anodes of the
diodes is combined together. Cathode of the first diode
is connected to the non-inverting terminal (Vin+) and
cathode of the second diode is connected to the inverting
terminal (Vin-). Biasing of the diode is done with the help
of applying current (Ibias) to the anodes terminal. Ibias and
Iabc terminal provides two additional achievements in the
OTA circuit.
The operational transconductance amplifier (OTA) is
voltage to current converter circuit. In the ideal condition
OTA, the output current linearly follows the differential
input voltage. The express of the output current Iout is
given as follows
Where Vin+ & Vin- represents the voltage at the noninverting input and inverting input terminals respectively
and gm represents the amplifier transconductance. The
amplifier's output voltage is expressed as:
The voltage gain is the ratio of output voltage divided by
differential input voltage, expressed as:
978-1-5090-4724-6/17/$31.00 ©2017 IEEE
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2017 Devices for Integrated Circuit (DevIC), 23-24 March, 2017, Kalyani, India
A. Operational Transconductance Amplifier
Operational Transconductance amplifier has many
applications in the integrated circuit such as in the
designing of low power circuit. It is used in designing of
active filters, portable devices, sensor implementation
and hearing aid implementation. There are many
performance parameters that are considered while
designing the circuits of Operational Transconductance
B. Power Consumption
Power consumption is the basic constraints of any type
of integrated circuit(IC). There is a trade-off between
power and performance of any kind of integrated
circuit(IC). The system cost is directly related to power.
In power dissipation, power is converted into heat and
then radiated away from the device. If an IC is
consuming more power, then a better cooling mechanism
would be required to keep the circuit in normal
conditions. Due to this generated heat, device may get
damaged on continuous use. There is three type of the
Power dissipation in CMOS circuits.
Static Power Dissipation
Static power dissipation depends on logical states of the
circuits and it is independent of switching activities. The
static power dissipation of a circuit is defined in terms of
device leakage current and the supply voltage. Total
static power dissipation is(5)
P =I V
Where Isat is the current that flows through the circuit
when there is no switching event and V DD is the supply
Short Circuit Power Dissipation
Short-circuit power dissipation in CMOS inverter occurs
for finite rise and fall times of input voltage waveforms.
A direct current path is formed, when both NMOS and
PMOS transistors are turned on in the circuit
simultaneously for a short duration of time during
switching, this causes a direct current path between
powers supply and ground. During [5], switching, the
current does not contribute to the charging and
discharging of capacitance and current components that
flow through both PMOS and NMOS transistor are
called short circuit components.
Dynamic Power Dissipation
Dynamic power dissipation is the result of power
dissipation during switching activity. The dynamic
power dissipation in CMOS circuits is mainly occurs
during the charging and discharging of load
capacitance. Consider the simple CMOS inverter and
assume that a step voltage with negligible rise and fall
time is applied. When input voltage switches from 0 to
VDD, the load capacitance is being discharged through
NMOS transistor as the NMOS transistor starts
conducting and PMOS transistor is turned off. Thus, the
current in load capacitance is equal to the instantaneous
drain current of the NMOS transistor.
C. Slew Rate
The slew Rate of an amplifier circuit is defined as the
maximum rate of change of the output voltage with
respect to time. Slew Rate is usually expressed in units
of V/µs.
Slew Rate =
D CMRR (Common Mode Rejection Ratio)
The Common Mode Rejection Ratio of a differential
amplifier defines the ability of the device to reject
common-mode signals. Common-mode signals appear
simultaneously and in-phase on both inputs of the
amplifiers. The CMRR should be kept high to amplify
differential signal in the presence of a possibly large
common-mode input. The CMRR of the OTA should be
as high as possible.
CMRR= Ad/Ac = 20log10(Ad/Ac ) dB
With the advancement in very large scale integrated
circuit technology, the requirement of the more efficient
integrated circuit is increasing now a days. The
requirement of the low power IC’s is increasing with the
increasing demand of battery operated electronics
products and portable devices in the electronic market.
The battery operated devices must be designed to work
on less power consumption because batteries provide
limited power supply to the devices. The battery life of
the portable devices affects with the higher power
consumption in the devices. The [8], demand of these
devices depends on various factor such that higher
speed, lower delay, low area, low power consumption,
small silicon area, longer battery life and high
reliability. Today [9], leakage power has become a key
issue in processor hardware and software design. The
major component of leakage, the sub-threshold current,
exponentially increasing with decreasing device
dimensions. So, the Leakage current, is a primary
concern for low power, high performance digital CMOS
circuits design.
2017 Devices for Integrated Circuit (DevIC), 23-24 March, 2017, Kalyani, India
Operational transconductance [10] amplifiers (OTAs)
are key building blocks in analog microelectronics. Rail
to rail operation is achieved through different type of
techniques. One of the most common power reduction
techniques is bulk driven technology. Bulk driven
technique [11] is used for the low power application.
Bulk driven transistor is same as to the gate driven
transistor but only difference that ac input signal in
applied to the bulk terminal for the creation of
conduction between source and drain terminal shown in
Figure 2. Bulk driven transistor requires the lower
amount of the threshold voltage than the gate driven
The basic two stage Operational Transconductance
amplifier is implemented with the 45nm technology is
shown in Figure 3. The basic 2 stage operational
transconductance amplifier is differential pair circuit. It
uses the current mirror concept. Transistors that uses the
current mirror circuit are designed for the having same
aspect ratio. It means that the width and length of the
transistors should be same. So that it follows the current
mirror law and both the transistors should have same
drain current Id. The Ibias is 50 µA used for designing of
operational Transconductance Amplifier. The bulk
driven technology is used to reduce the threshold voltage
requirement for the Transistor. It also provides facility of
the rail to rail input range. It means that we can input
operating range from the 0.7V to 0.35V without affecting
the performance parameter of OTA
Figure 2. Bulk-driven NMOS transistor, (a) circuit operation;
(b) cross section
Bulk-driven circuits are typically used to handle the
issues of poor signal swing in such cases [7]. The limit
of the minimum threshold voltage is increased with the
Bulk driven technology that is the advancement in the
gate driven technology where voltage supply
requirement is limited by the threshold voltage. The
result of this concept is that bulk-driven transistor
operates on the same principle as junction-field-effecttransistor (JFET) is operated in its depletion mode. For
[7], illustration purposes, a cross sectional view of the
bulk-driven transistor are shown in Fig. 3(b). This
operation reduces the threshold limit of the gate –driven
MOSFETs where the bulk-to-source junction can be
either positive, zero or negative biased while still acting
as the high impedance node on condition that the
junction parasitic lateral and vertical BJTs are not fully
turned on. PMOS devices can be used as bulk-driven
transistors [12-13].
Figure 4 Basic Two stage Operational Transconductance
Amplifier schematic
The proposed bulk driven OTA is implemented with the
help of 45nm technology shown in Figure 5. The Supply
Voltage is given to the bulk terminal and bias voltage is
given to the gate terminal. The specification of the
transistor is W= 45nm, and L= 120nm. Ibias current is
50µA for designing of the two stage Operational
Transconductance amplifier.
978-1-5090-4724-6/17/$31.00 ©2017 IEEE
2017 Devices for Integrated Circuit (DevIC), 23-24 March, 2017, Kalyani, India
Figure 7. Power Consumption waveform of the two state OTA
Noise performance of the bulk driven two stage operational
transconductance amplifier is shown in Figure 8.
Figure 5 Bulk Driven Operational Transconductance
Amplifier circuit schematic
The circuit is designed with the help of supply voltages
range from 0.7V to 0.35 V at operating frequency of 100
MHz. The transient response for the proposed OTA is
shown in Figure 6. Where Net13 represents the input
waveform and Vout is the amplified output waveform.
Figure 8 Noise waveform of the two state OTA
Figure 6 Transient response of operational Transconductance
Figure 7 shows the power consumption waveform of two
state bulk driven Operational Transconductance
Amplifier for 0.7V Supply voltage.
Figure 9 Waveform of leakage current the two state OTA
978-1-5090-4724-6/17/$31.00 ©2017 IEEE
2017 Devices for Integrated Circuit (DevIC), 23-24 March, 2017, Kalyani, India
show that power consumption of the bulk driven
operation amplifier is lower than the other the basic
OTA. Transconductance of the bulk driven operational
transconductance amplifier is higher that the basic
operational transconductance amplifier but the slew rate
of the bulk driven is slightly lower than the basic
operational transconductance amplifier.
Figure 10 Layout of the 2 stage Basic Operational
Transconductance Amplifier
Figure 9 shows the leakage current wave form the two
stage operational transconductance amplifier. Leakage
power is calculated from the value of the leakage current.
It is observed from the waveform in Figure 10 is that the
value of the leakage current and leakage power is
reduced in the bulk driven operational transconductance
amplifier. Figure 10, 11 indicates the layout of the basic
two stage operational transconductance amplifier and
bulk driven two stage operational transconductance
From the Table I it is shown that power consumption is
reduced by 60.15% in the bulk driven operational
conventional Operational Transconductance amplifier
circuit without degrading the performance parameter of
the circuit such as leakage current and leakage power and
transconductance. But other parameter such as noise and
slew rate is slightly degraded which is shown in fig. 12.
The leakage current obtained for the proposed bulk
driven operational transconductance amplifier is better
than conventional operational tranconductance amplifier
but Speed of the bulk driven operational
transconductance amplifier transistor is lower than that
of the conventional operational transconductance
amplifier. Finally there is the trade of between the power
and speed. For the low power application bulk driven
operational transconductance amplifier is better choice
A. TABLE I Comparative Analysis of Basic OTA
with bulk driven OTA
Figure 11 Layout of the 2 stage Bulk driven Operational
Transconductance Amplifie
Table I shows the simulated result of 2 stage Operational
Transconductance amplifier for Basic operational
Transconductance amplifier comparing with the bulk
driven Transconductance amplifier. The proposed OTA
is implemented on 45nm CMOS technology. Table 1
Basic Two
stage OTA
Bulk-Driven Two
stage OTA
2017 Devices for Integrated Circuit (DevIC), 23-24 March, 2017, Kalyani, India
Slew Rate
Basic OTA
Bulk Driven OTA
Figure 12 Performance Parameter of Basic OTA with the
Bulk driven OTA
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