Miriam Pekar Alex Liberchuk Supervisors: Dr. Alexander Fish Mr. Arthur Spivak 10/2011 P

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 Imaging Dynamic 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 ⋅ 2 EXP. 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 Suitable Comparator Topologies Design Procedures Set-up to determent W/L (each Topology) Full SPECTRA simulation 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 = MHz Slew Rate > 1.8 V/µsec Power Dissipation < 100nW C Load = 150 fF 0V < V out < 3.3V 0.2V < V in < 2V

Project Process Flow Specifications Choose Suitable Comparator Topologies Design Procedures Set-up to determent W/L (each Topology) Full SPECTRA simulation Remaining Tasks

Comparator Topologies  Simple One-Stage  Two-Stage  Folded Cascode  Gain Boosted Folded Cascode

Project Process Flow Specifications Choose Suitable Comparator Topologies Design Procedures Set-up to determent W/L (each Topology) Full SPECTRA simulation 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 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 Power Dissipation ENABLE = ONENABLE=OFF GBW = Gain*BW= (60.12dB)*1.36MHz = 1.379GHz

Project Process Flow Specifications Choose Suitable Comparator Topologies Design Procedures Set-up to determent W/L (each Topology) Full SPECTRA simulation 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 Suitable Comparator Topologies Design Procedures Set-up to determent W/L (each Topology) Full SPECTRA simulation 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.

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