design of a high precision comparator for implementation of a wdr sensor
DESCRIPTION
Miriam Pekar Alex Liberchuk Supervisors: Dr. Alexander Fish Mr. Arthur Spivak. Design of a High Precision Comparator for Implementation of a WDR Sensor. P-2011-130. 10/2011. What is an Image Sensor?. - PowerPoint PPT PresentationTRANSCRIPT
Miriam PekarAlex Liberchuk
Supervisors:Dr. Alexander FishMr. Arthur Spivak
10/2011
P-2011-130
What is an Image Sensor?
An image sensor is a device that converts an optical image into an electronic signal. It is used mostly in digital cameras and other imaging devices.
The two most popular kinds of image sensors are:Charge-coupled device (CCD).Complementary Metal–Oxide–
Semiconductor (CMOS).
Why CMOS and not CCD? CMOS is implemented using less components. CMOS sensors consume less power. This is important in portable devices. Provides faster readout. Cheaper to manufacture.
CMOS sensors, traditionally, are more susceptible to noise. Light sensitivity of a CMOS chip tends to be lower because
several transistors are located next to each photodiode. CMOS sensors tend to have Low Dynamic Range.
CMOS Drawbacks:
Effects of Low Dynamic Range Imaging:
Goal of Our Project: Improve the Dynamic Range of the CMOS Sensor
Low DR Imaging
Wide DR ImagingDynamic Range quantifies the ability
of a sensor to image highlights and shadows.
What is a CMOS Sensor? It is an image sensor produced by a CMOS
semiconductor process. It consists of a photodiode and extra circuitry next
to each photodiode converting the light energy to a voltage, later the voltage is converted to a digital signal.
What is a Comparator?
a comparator is a device that compares two voltages and switches its output to indicate which is larger.
A good comparator implementation can be an Operational Amplifier connected in open loop.
The Use of the Comparator in a WDR Sensor:
If a pixel value exceeds the threshold - i.e. the pixel is expected to be saturated at the end of the exposure time - the reset is given at that time to that pixel. The binary information concerning the reset (i.e., if it is applied or not) is saved in a digital storage for later calculation of the scaling factor. Thus, we can represent the pixel output in the following floating- point format: M⋅2EXP. Here, the mantissa (M) represents the digitized pixel value, and the exponent (EXP) represents the scaling factor.
This way, the maximal signal value the sensor can process is raised – higher DR.
Project Process Flow
Specifications
Choose SuitableComparatorTopologies
Design ProceduresSet-up to determentW/L (each Topology)
Full SPECTRAsimulation
Remaining Tasks
Our Project:
Design a High Precision Comparator to Implement a WDR Sensor
Technology - TOWER 180nm The Comparator’s Design Requirements:
GBW = 1-2 GHz Gain = 1000 Bandwidth = 1 - 2 MHz Slew Rate > 1.8 V/µsec Power Dissipation < 100nW
CLoad = 150 fF
0V < Vout < 3.3V
0.2V < Vin < 2V
Project Process Flow
Specifications
Choose SuitableComparatorTopologies
Design ProceduresSet-up to determentW/L (each Topology)
Full SPECTRAsimulation
Remaining Tasks
Comparator Topologies
Simple One-Stage Two-Stage Folded Cascode Gain Boosted Folded Cascode
Project Process Flow
Specifications
Choose SuitableComparatorTopologies
Design ProceduresSet-up to determentW/L (each Topology)
Full SPECTRAsimulation
Remaining Tasks
Simple One-Stage Comparator
The topology resulted in poor performance, due to poor gain and bandwidth
Two-Stage Comparator
Current Mirror
Differential Pair
Active Load
Common Source
Amplifier
Enable Switch
Bias Current
Two-Stage Comparator cont. Results:
All the design requirements were met!
Gain, BW
3.275[ ]dVout VSR Secdt
Slew Rate
ENABLE=ON
Power Dissipation
ENABLE=OFF
GBW = Gain*BW= (62.03dB)*1.4MHz = 1.769GHz
Folded Cascode Comparator
Bias Circuit
Differential Pair
Current Source
Current Mirror
Cascode Transistors
Common Source
Amplifier
Folded Cascode Comparator cont.
Results:
All the design requirements were met!
Gain, BWSlew Rate
2.53[ ]dVout VSR Secdt
Power Dissipation
ENABLE = ON ENABLE=OFF
GBW = Gain*BW= (60.12dB)*1.36MHz = 1.379GHz
Project Process Flow
Specifications
Choose SuitableComparatorTopologies
Design ProceduresSet-up to determentW/L (each Topology)
Full SPECTRAsimulation
Remaining Tasks
Full SPECTRA simulation DC analysis – make sure all transistors
are in saturation mode AC analysis – find a suitable W/L for the
desired Gain, BW and GBW. Transient analysis – checks the Slew
Rate, and Power Dissipation. Now, Corners were checked.
Project Process Flow
Specifications
Choose SuitableComparatorTopologies
Design ProceduresSet-up to determentW/L (each Topology)
Full SPECTRAsimulation
Remaining Tasks
Remaining Tasks
Create and check Gain Boosted Folded Cascode topology.
Comparison of all topologies designed in this project.
Layout Implementation of the best topology and post layout simulations.
Questions
תודה רבה!