Design of offset Compensated CMOS CFOA

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Design of offset Compensated CMOS CFOA

• Dr. Ali Assi,
• Advisor
• Dr. Mamdouh Ghannam , coordinator

• Aisha Mubarak
• Fatma Hassan
• Fawziea Abdulla
• Muna Bakri

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Presentation Agenda

• Introduction
• Objective
• Types of Amplifiers
• Applications of Op Amp.
• Why CMOS?
• Circuit Biasing.
• CFOA with Compensation circuit Block diagram
• Definition of CFOA
• Simulation Results of CFOA circuit.
• Compensation Circuit
• Compensation Circuit Definition.
• Proposed Compensation Circuit..
• Block diagram of the compensation circuit..
• VC VIC circuit.
• CIM circuit.
• Conclusion

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Objective

• The main objective of this project is
  designing and simulating a low-offset
  compensation CMOS circuit of current feedback
  amplifier (CFOA) .

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• Types of Amplifiers

CFOA a closed-loop configuration in which the
error signal used for feedback is in the form of
a current. VFOA a closed-loop configuration in
which the error signal is in the form of a
voltage
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Applications

• Amplifiers are used in
• Wireless communications broadcasting
• Audio equipment of all kinds.
• Coax cable driver.
• Video amplifier.
• Flash ADC buffer.
• Scanner and Imaging systems.

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Implementation of OP AMPs

• Three technologies

• BJT Technology.
• CMOS Technology.
• BiCMOS Technology.

0.35 micron CMOS Technology
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Why CMOS?
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Circuit Biasing
P_MOS
N_MOS
VSG gt Vth VSD gt VSG-Vth
VGS gt Vth VDS gt VGS-Vth
Vth 0.544
Vth -0.714
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Block diagram of the CFOA with the Compensation
circuit
CFOA
Vp
Vout
Vn
Icp
Icn
Compensation Circuit
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Architecture of CFOA

• Block diagram of the CFOA

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Top Level of the CFOA
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Implementation of CFOA
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The Frequency Response of the CFOA
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Results of CFOA

• CFOA was designed using 0.35 µm technology.

• High gain 55.5 dB

• Large BW 2.1 MHz

• Offset voltage 8 mV

• Low power dissipation 0.4 mW

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Compensation Circuit

• The compensation circuit will reduce the
  offset voltage of the CFOA. In fact, low offset
  voltage is a desirable characteristic in
  operational amplifiers used in applications that
  require accuracy.

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Compensation Circuit

• In general, an offset compensation circuit
  reduces the offset voltage that appears at the
  output of an amplifier.

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Proposed Compensation Circuit

• The proposed compensation method is based on a
  combination of two techniques
• Error integration.
• Current feedback.

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Detailed Block Diagram of Compensation Circuit
CFOA
Icn
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Top Level of the Compensation Circuit
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Implementation of Compensation Circuit
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VC VIC Circuit

• VC-VIC Voltage Comparator and Voltage to Current
  Converter
• The VC-VIC takes the difference between Vp and Vn
  (i.e. the input offset voltage) and convert it
  into a current.

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Top level of VC - VIC
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Schematic of VC - VIC
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Schematic of VC VIC1
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CIM Circuit

• CIM Current Integrator Memory
• The CIM block integrates this error and feeds it
  back into the CFOA to compensate the input offset
  voltage.

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Top level Circuit (CIM)
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CIM Circuit
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Results of the CFOA with and without compensation
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Results
Offset improvement
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Results
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Results
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Results
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Budget Study
Project Cost estimating is important reflected
on the decisions to be taken.
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Proposed Budget
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Proposed Budget
The total estimated cost of the project is
254,000 Dhs
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Conclusion

• A CMOS Current Feedback Operational Amplifier
  (CFOA) using the 0.35µm technology has been
  simulated.
• OrCAD IC design tool and transistors models from
  MOSIS have been used.

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Conclusion

• The offset compensation method used here is
  based on a combination of error integration
  current feedback methods.
• The offset voltage is detected and converted into
  current using the VC-VIC circuit.
• The current is integrated and fed back into the
  CFOA using the CIM circuit.

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Conclusion

• CFOA was designed using 0.35 µm.

• High gain 55.5 dB
• Large BW 2.1 MHz
• Low Power dissipation 0.8 mW.

• Compensation circuit reduces the voltage offset
  and improves the gain.

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Recommendations

• Design of ICs is an important domain that is
  getting interest in the UAE and attracting
  students (DSO).
• Universities and Students have to do something
  about it

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Its time to decide what to do!
Universities

• Have undergraduate Microelectronics option in
  their curriculum,

• Encourage students to choose the Microelectronics
  option,

• Microelectronics Master program,

• Start building separate VLSI labs dedicated for
  Integrated Circuits design,

• Collaboration with the DSO.

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Its time to decide what to do!
Students

• Do not hesitate.

• Believe in the DSO as one of the most important
  industrial development of the UAE,

• Start showing interest in courses related to the
  Microelectronics,

• Have plans for higher studies in the
  Microelectronics,

• Get familiar with circuits design tools available
  at your site,

• Be updated with recent developments in the
  Microelectronics area (Internet).

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Thank You