Introduction Transformer [2] The output of the step-up transformer

Introduction

Background of Charge Pump

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

 

            Electricity is a very
crucial element in our daily life as most of the devices and equipment requires
electricity to operate. Electronic devices become smaller and portable as
technology advance. As a result, some electronic devices require lower supply
voltage to operate. However, some system blocks in electronic devices such as
flash memories, audio and video codec and so forth still require higher voltage
to operate 1. A system block that can generate high output voltage from low
supply voltage is needed. Thus, charge pump is introduced to generate those
output voltage.

            Before charge pump is
introduced, transformer is widely used in producing a higher output voltage
from a small input voltage through electromagnetic induction. Transformer can
be a step-up transformer or a step-down transformer based on the design. A
step-up transformer is a transformer that produces a higher output voltage from
a lower input voltage while step-down transformer is a transformer that
generates lower output voltage from a higher input voltage. Figure 1.1 below
shows a step-up transformer.

Figure 1.1: Step-Up Transformer 2

            The output of the
step-up transformer depends on the ratio of number of turns from secondary
winding to primary winding. In Direct Current (DC) electronics circuit, using
transformer is not an efficient process as transformer only works with
Alternating Current (AC) voltage source. Implementing transformer in DC electronics
circuit will requires rectifier to convert AC voltage source to DC voltage
source which causes the circuit to become heavier and larger 1.

            A simple charge pump
can be design using switches and capacitor. Figure 1.2 shows a simple one stage
charge pump.

Figure 1.2: Simple One Stage Charge Pump 3

            During
first half clock phase of CLK, VCK will be zero, switch S1
will be closed and switch S2 will be opened and capacitor, C will be
charged to the supply voltage, VDD. In the second half clock phase
of CLK, VCK will be VDD, switches S1 will be opened
and S2 will be closed and the voltage charged at the capacitor will
discharge through Vout as the bottom plate of capacitor assumes a
potential VDD. Thus, the voltage at Vout will now become
2 VDD. The charge pump in Figure 1.2 is also known as a voltage
doubler as the voltage produced at Vout is twice the supply voltage,
VDD.

            A
higher output voltage can be achieved by cascading the charge pump. Figure 1.3
below shows a N-stage charge pump.

Figure 1.3: N-stage Charge Pump 3

           

            The
general equation in calculating the output voltage of N-stage charge pump is as
follows:

 

Energy Harvesting

            Energy harvesting is
collecting and converting of small ambient energy that is well characterized
and regular into electrical energy. Examples of energy harvesting technologies
are solar energy harvesting, wind energy harvesting, vibration energy harvesting,
thermoelectric energy harvesting and so forth.

            Wind energy harvesting
technologies convert kinetic energy into electrical energy. An example of
application of wind energy harvesting is wind turbine. A wind turbine is made
out of 3 blades mounted at the top of tubular steel. To ensure the wind turbine
take advantage of the faster wind speed, it is normally placed 100 feet above
the ground 4. As the turbine catch wind energy, the rotor rotates and
produces alternating current (AC) voltage.    

            Solar energy harvesting
technologies harvest sunlight as the source of energy and convert it into
electrical energy using semiconductor materials. Semiconductor materials that
exhibit a photovoltaic (PV) effect can be used to convert solar radiation into
electricity through a photovoltaic process 5. Photovoltaic effect generate
electricity by exciting electrons into a higher energy state, allowing them to
act as positive and negative charge carriers to produce direct current (DC).

             Piezoelectric is an application of vibrational
energy harvester. It produces alternating current (AC) from mechanical strain.
The mechanical strain can be generated from sole shoes during walking, vehicles
such as helicopter and train. In industrial application, it is use to alert the
need of maintenance of machine 6. 

            Thermoelectric energy
harvesting generates electricity from the surrounding temperature. Thermoelectric
generator (TEG) is use to harvest the surrounding temperature. It is suitable
to be implement in low voltage application as the voltage generated is direct
current (DC) type and can be used as a directly source of supply.

            There are lots of
energy harvesting technologies but not all the technologies are suitable to
implement charge pump in it as energy harvesting technologies such as wind and
vibrational generate AC type electrical power where charge pump is a DC-DC
voltage booster. Implementing charge pump in those technologies will make the
circuit bigger and complex.

 

Problem Statement

            Wireless
sensors are widely employed in various application including environmental,
medical, automotive and security monitoring 7. Battery have been use as a
source of power supply but it is inconvenient to implement as battery
replacement is needed every once in a while. Thus, energy harvesting is an
alternative solution to power the wireless sensors.

            In
biomedical field, pacemaker is a device that controls your heartbeats rate by
sending electrical pulse. Pacemaker is needed for people with too slow or too
fast heartbeats and irregular heartbeats. A pacemaker requires a battery of
2.8V to operate for 10.4 years 8. If thermoelectric harvesting can be
implement in pacemaker, patients would not need to replace the battery as they
can generate electricity from their body temperature.

            Normally,
the output voltage of TEG is only hundreds of mV which is not enough to power
up a pacemaker 7. Thus, a charge pump is needed to pump up the voltage. This
project will demonstrate how charge pump work and become a crucial component in
energy harvesting technologies.

 

Objectives

            The objectives of this project are:

                      
i.           
To design Dickson Charge Pump with Forward Body
Biased and to make a comparison study with Dickson Charge Pump.

                    
ii.           
To explore the architecture of charge pump
through schematic, layout and simulation in Synopsys Electronic Design
Automation (EDA) Tool.

 

Expected
Outcome

            The expected outcomes of this
project are to produce an output voltage, 3V with the optimum number of stages
and to provide an output current of 250µA to operate ultra-low
voltage applications.

 

Project
Scope

            The
scopes of the project are:

       
i.           
To draw schematic and layout of charge pump
using Synopsys EDA Tool.

     
ii.           
To produce an output voltage that is sufficient
to power low voltage applications of 3V from input voltage of 100mV with
minimum number of stages.

 

Project Outline

            Chapter
1 is introduction and background of the project, starting from the introduction
of charge pump and energy harvesting, problem statements, objectives of the
project, expected outcomes and project scopes.

             Chapter 2 is literature review on the charge
pump technologies and a comparison of charge pumps. This chapter will also
briefly introduce Synopsys EDA Tool.

            Chapter
3 is research methodology that provides the workflow of the project. This
chapter also discuss about the method of using Synopsys.

            Chapter
4 is results and discussion. The result obtained from simulation of charge pump
using Synopsys EDA Tool is analysed and explained in details.

            Chapter
5 will provides the conclusion and recommendation of the project for future
improvement.