REVIEW – PART 2

Introduction Energy Harvesting (EH)

• Energy harvesting (also known as power harvesting or energy scavenging) is the process in which energy is captured from a system's environment and converted into usable electric power.

• EH allows electronics to operate where there's no conventional power source, eliminating the need for wires or replacement of batteries.

• EH systems generally includes circuitry to charge an energy storage cell, and manage the power, providing regulation and protection.

• EH-powered systems need reliable energy generation, storage and delivery:

• Must have energy storage as EH transducer energy source is not always available (solar at night, motor vibration at rest, air-flow, etc.)

• EH can provide “endless energy” for the electronics lifespan.• Ideal for substituting for batteries that are impractical, costly,

or dangerous to replace.

How Energy Harvesting works?An energy harvester comprises one or more transducers, power conditioning, and energy storage. These technologies work together to collect energy and deliver power to the device. On the other hand, the device which uses the energy needs to be designed to work with energy harvesting as the power source.

(Sources of Energy)

(Devices)

How Energy Harvesting works?

• The transducer: converts energy from one energy type to a another energy type, usually electricity.

• Power conditioning: is necessary because the natural output of the transducer can be intermittent, and at the wrong frequency, voltage and current to directly drive the device. A specialised DC-DC converter microchip takes in power from the transducer and convert to voltages which can then be stored or used.

• Energy storage: is needed to balance the energy supply and energy demand. For applications where energy is used as soon it is collected (e.g. RFID and wireless light switches), no storage is needed. Usually however a rechargeable battery, capacitor, or supercapacitor is used. Batteries degrade over time, and so the lifetime of the storage device can often be the limiting factor in the overall lifetime of the harvester.

Energy harvesting uses unconventional sources to power circuitry.

• Light (captured by photovoltaic cells)

• Vibration or pressure (captured by a piezoelectric element)

• Temperature differentials (captured by a thermo-electric generator)

• Radio Frequency (captured by an antenna)

• Biochemically produced energy (such as cells that extract energy from blood sugar).

Sources of Energy

Energy Harvesting Block Diagram

Biochemical Energy Production

• Catabolism: metabolic reactions in which large molecules are broken down into smaller molecules – Usually produce energy (but not always)

• Anabolism: metabolic reactions in which smaller molecules are joined to form larger molecules – Usually consume energy

Metabolism

• Almost all energy-harvesting scenarios require some sort of energy storage element or buffer. Even if the voltage and current requirements of an embedded application were so low as to be run directly on power captured or scavenged from the environment, such power would not flow in a constant way.

• Storage elements or buffers are implemented in the form of a capacitor, standard rechargeable lithium battery, or a new technology like thin-film batteries. What kind of energy storage is needed depends greatly on the application.

• Some applications require power for only a very short period of time, as short as the RC time constant discharge rate of a capacitor. Other applications require relatively large amounts of power for an extended duration, which dictates the use of a traditional AA or a rechargeable lithium battery

Energy Storage is a Must

Li-Ion Battery

Thin Film Battery

Super Cap

Recharge cycles Hundreds Thousands Millions

Self-discharge Moderate Negligible High

Charge Time Hours Minutes Sec-minutes

Physical Size Large Small Medium

Capacity 0.3-2500 mAHr12-1000 μAHr 10-100 μAHr

Environmental Impact

High Minimal Minimal

Solar cell 

A solar cell is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect.The solar cells that you see on calculators and satellites are also called photovoltaic (PV) cells, which as the name implies (photo meaning "light" and voltaic meaning "electricity"), convert sunlight directly into electricity.

Solar Cells: Converting Photons to Electrons

Solar cells are made of the same kinds of semiconductor materials, such as silicon, used in the microelectronics industry. For solar cells, a thin semiconductor wafer is specially treated to form an electric field, positive on one side and negative on the other. When light energy strikes the solar cell, electrons are knocked loose from the atoms in the semiconductor material. If electrical conductors

are attached to the positive and negative sides, forming an electrical circuit, the electrons can be captured in the form of an electric current -- that is, electricity. This electricity can then be used to power a load, such as a light or a tool.

• A module is a group of cells connected electrically and packaged into a frame known as a solar panel.

• Modules are designed to supply electricity at a certain voltage, such as a common 12 volts system. The current produced is directly dependent on how much light strikes the module.

• Multiple modules can be wired together to form an array.

• Solar panels or arry can be connected in both series and parallel electrical arrangements to produce any required voltage and current combination.

Solar Cells: Converting Photons to Electrons

A solar system consists of: Solar Panels, a Charger Controller, a Power Inverter, andBatteries.• Solar Panels: supply the

electricity and charge the batteries. A very small system could get away with a couple 240 watt panels but figure at least 4 to 8 for a small to medium system.

• Charge Controller: is needed to prevent overcharging or draining too much of the batteries. Proper charging will prevent damage and increase the life and performance of the batteries.

• Power Inverter: is the heart of the system. It makes 120 volts AC from the 12 volts DC stored in the batteries. It can also charge the batteries if connected to a generator or the AC line.

Typical Solar Power Setup

• Batteries: store the electrical power in the form of a chemical reaction. Without storage you would only have power when the sun was shining or the generator was running.

A single solar cell produces only about 1/2 of a volt. However, a typical 12 volt panel about 25 inches by 54 inches will contain 36 cells wired in series to produce about 17 volts peak output. If the solar panel can be configured for 24 volt output, there will be 72 cells so the two 12 volt groups of 36 each can be wired in series, usually with a jumper, allowing the solar panel to output 24 volts. When under load (charging batteries for example), this voltage drops to 12 to 14 volts (for a 12 volt configuration) resulting in 75 to 100 watts for a panel of this size.Multiple solar panels can be wired in parallel to increase current capacity (more power) and wired in series to increase voltage for 24, 48, or even higher voltage systems. The advantage of using a higher voltage output at the solar panels is that smaller wire sizes can be used to transfer the electric power from the solar panel array to the charge controller & batteries. Since copper has gone up considerably in the last few years, purchasing large copper wiring and cables is quite expensive. (that's why pennies are made of mostly zinc today).

EXAMPLES

EH Summary

EH Summary

EH Summary

When is energy harvesting appropriate?

Energy harvesting – a great solution Energy harvesting is useful when: • There is a match between the available energy and the energy needed • Energy harvesting provides a benefit that is not achievable using batteries or grid electricity

Energy harvesting – not a great solution • Free energy often comes at a cost, and thinking through the complete system is key to determining whether energy harvesting is going to solve your power needs.

Green energy A myth that keeps cropping up is that energy harvesting is a small scale demonstration of how we can collect freely available energy in the environment, and that in the future these same technologies will be scaled up and used to power our homes and businesses. This is false. With the exception of photovoltaic cells for collecting sunlight, the technologies are completely different.

• A number of different wireless technologies have been developed for very short distances. These are referred to as 'short-range wireless communication.'

• Short-range wireless communication uses signals that travel from a few centimeters to several meters.

• In contrast, signals in medium-range wireless communication travel up to 100 meters or so, while signals in wide-area wireless communication can travel from several kilometers to several thousand kilometers.

Short-Range Wireless

• Radio-Frequency Identification (RFID) is the use of radio waves to read and capture information stored on a tag attached to an object.  A tag can be read from up to several feet away and does not need to be within direct line-of-sight of the reader to be tracked. 

• The RFID device serves the same purpose as a bar code or a magnetic strip on the back of a credit card or ATM card; it provides a unique identifier for that object. And, just as a bar code or magnetic strip must be scanned to get the information, the RFID device must be scanned to retrieve the identifying information.

• RFID mostly use frequency ranges: • LF: 125-134KHz• HF: 13.56MHz• UHF: 860-915MHz

What is RFID?

A RFID system consists of:• A tag or label.• A reader.

RFID tags or labels are embedded with a transmitter and a receiver. The RFID component on the tags have two parts: a microchip that stores and processes information, and an antenna to receive and transmit a signal. The tag contains the specific serial number for one specific object. 

How RFID Works

To read the information encoded on a tag, a two-way radio transmitter-receiver (called an interrogator/reader emits a radio-frequency signal in a relatively short range to the tag using an antenna. In case of passive RFID tag, the RF radiation also provides the energy to the passive RFID tag to communicate. The tag responds with the information written in its memory bank. The interrogator will then transmit the read results to an RFID computer program.

How RFID Works

• NFC IS A SHORT RANGE HIGH FREQUENCY WIRELESS TECHNOLOGY THAT CARRY SECURE TWO-WAY INTERACTIONS BETWEEN ELECTRONIC DEVICES.

• NFC PROVIDES CONTACT OR CONTACTLESS COMMUNICATION IN A PROXIMITY OF A FEW AND UP TO 10 CENTIMETERS.

• NFC IS MAINLY AIMED FOR MOBILE OR HANDHELD DEVICES.

• NFC ALLOWS COMMUNICATION BETWEEN:

• TWO POWERED (ACTIVE) DEVICES

• POWERED AND NON SELF-POWERED (PASSIVE) DEVICES.

• NFC UTILIZES ELECTROMAGNETIC RADIO FIELDS WHILE TECHNOLOGIES SUCH AS BLUETOOTH AND WI-FI FOCUS ON RADIO TRANSMISSIONS INSTEAD.

• NFC OFFERS THE ULTIMATE IN SECURITY AND CONVENIENCE, AND MAKES NEW INTERACTIONS POSSIBLE.

WHAT IS NFC?

FEATURES

• NFC is an offshoot of RFID with the exception that NFC is designed for use by devices within close proximity to each other

• NFC combines the interface of a smartcard and a reader into a single device that allows two-way communication between endpoints, where RFID system was one-way only.

• NFC devices operate at 13.56MHz, with a bandwidth 14kHz.

• NFC supports data rates: 106, 212 and 424 Kbits/s• For two devices to communicate using NFC, one

device must have an NFC reader/writer and one must have an NFC Tag.

There are two types of RFID tags: • Passive or non-battery powered RFID tag• Passive or battery powered RFID tag

RFID tags

Active NFC Devices

Active NFC device usually a microcontroller based like a NFC enabled smartphone, would not only be able to collect information from NFC tags, but it would also be able to exchange information with other compatible phones or devices and could even alter the information on the NFC tag if authorized to make such changes.

NFC reader continuously emits RF carrier signals and keeps observing the received RF signals for data.

A passive device, such as an NFC tag, contains information that other devices can read but does not read any information itself. NFC tag does not have its own power source. It absorbs energy emitted by the reader(phone) and starts sending modulated information when sufficient energy is acquired from the RF field generated by the reader. Data modulation (0s and 1s) is accomplished by either direct modulation or FSK or Phase modulation.

Passive NFC Device

1.Convenience: Many consumers will "pay" for convenience because convenience is very important in today's society. NFC is a perfect source of convenience because it merges a mobile device with wallet(s). NFC is also quite intuitive; all it takes is a simple touch when using NFC for payments. Can you imagine how much faster line ups would be at the grocery store, coffee shop, etc?2. Versatility: NFC can be well adapted for all kinds of situations ranging from bank cards to transit passes, movie passes, reward systems and even keys. Ideally, NFC is suited for a broad range of industries and uses because this innovation allows users to manipulate through the development of software.3. Safety:  Now, you might think how could fusing your wallet into your mobile device be safer. After all, just like a wallet, a cellphone could be stolen. However when your wallet is stolen, the thief has access to all your credit cards and information right away! With smartphones, passwords can be used to further protect your information. 

• NFC enabled credit cards are much more secure than a credit card magnetic strip 

• Requires PIN• Retailers no longer have physical access to your credit card

information

Advantages of NFC

Disadvantages of NFC

1. Company Agreements to use NFC: Many of us who would like to try out NFC wishes that it can be used everywhere and anywhere. However if companies do not agree to integrate NFC into their business, consumers will not be able to use the technology. 2. Security: • Another major risk to NFC is computer hacking or phone

hacking. As mobile phones become more developed, they become much like a hand held computer, and as with computers, they become prone to viruses. Hackers will want to gain access to these tiny computers because it contains a lot of important information all in one device. 

• Examples include a phone’s owner credit card information, bill payments, social security information, etc. Moreover, as technology advances, it will becomes easier for hackers to do this. 

3. Limitations: NFC can be operated under short range (< 10 cm) with data rate is very less at about 106, 212 and 424kbps.

• Mobile handsets are primary target for NFC and soon NFC will be implemented in most handheld devices. Even though NFC has the shortest range among radio frequency technologies, but it is revolutionary due to its security, compatibility, user friendly interface, immense applications, etc.

• The advancements in mobile wireless technology and communication standards have enabled usage of contactless and NFC based payment models.

• The mobile wallet based payment model is gaining considerable momentum and is currently being seen as one of the key payment model, to promote contactless payment processing practices.

• The mobile wallet technology enables the end-users to make payments with their mobile wallet accounts, without having to use credit or debit cards and hence this technology can also help users that do not use credit or debit cards.

Conclusion

PHASE LOCK LOOP

EE174 – SJSU

TAN NGUYEN

OBJECTIVES

• Introduction to Phase-locked loop (PLL)

• Historical Background• Basic PLL System

• Phase Detector (PD)• Voltage Controlled Oscillator

(VCO)• Loop Filter (LF)

• PLL Applications

• PLL is also referred as frequency synthesizer.• PLL is a circuit that locks the phase of the output to the input.• PLL is a negative feedback control system where fout tracks fin and rising edges of input clock align to rising edges of output clock• PLL is a circuit synchronizing an output signal with a reference or input signal in frequency as well as in phase.

• In the synchronized or “locked” state, the phase error between the oscillator’s output signal and the reference signal is zero, or it remains constant.

• If a phase error builds up, a control mechanism acts on the oscillator to reduce the phase error to a minimum so that the phase of the output signal is actually locked to the phase of the reference signal. This is why it is called a phase-locked loop.

Introduction to Phase-locked loop (PLL)

The basic PLL block diagram consists of: • A phase detector (PD) and phase frequency detector (PFD)• A voltage-controlled oscillator (VCO) • A loop filter (LF)

Basic PLL System

Phase Detector• Compares the phase at each input and generates an error

signal, e(t), proportional to the phase difference between the two inputs. Loop filter extracts the average value and feeds to VCO. KD is the gain of the phase detector (V/rad).

• The transfer characteristic of such a phase detector is shown below. Note that in many implementations, the characteristic may be shifted up in voltage (single supply/single ended).

Ve(t) = KD [Φout(t) - Φref(t)]

•If the phase difference is π/2, then the average or integrated output from the XOR-type phase detector will be zero (or VDD/2 for single supply, digital XOR). The slope of the characteristic in either case is KD.

Phase Detector Gain

KD (PC1) = VCC / π KD (PC2) = VCC / 2π

Phase comparator conversion gain factor expressed in units of V/rad. KD is determined by:

VD = KD (Φi – ΦO) orKD = VD / (Φi – ΦO)

Example:An analog multiplier or mixer can be used as a phase detector. Recall that the mixer takes the product of two inputs.

ve(t) = A(t)B(t) where A(t) = A cos(ω0t + φA)

B(t) = B cos(ω0t + φB)

Then, A(t)B(t) = (AB/2)[ cos(2ω0t + φA + φB) + cos(φA - φB)]

Since the two inputs are at the same frequency when the loop is locked, we have one output at twice the input frequency and an output proportional to the cosine of the phase difference. The doubled frequency component must be removed by the low pass loop filter. Any phase difference then shows up as the control voltage to the VCO, a DC or slowly varying AC signal after filtering.

In PLL applications, the VCO is treated as a linear, time-invariant system. Excess phase of the VCO is the system output. The VCO oscillates at an angular frequency, ωout. Its frequency is set to a nominal ω0 when the control voltage is zero. Frequency is assumed to be linearly proportional to the control voltage with a gain coefficient KO or KVCO (rad/s/v).

ωout = ω0 + KO Vcont

where ω0 is the center (angular) frequency of the VCO and KO is the VCO gain in rad /s V.

VCO

To obtain an arbitrary output frequency (within the VCO tuning range), a finite Vcont is required. Let’s define φout – φin = φο. The XOR function produces an output pulse whenever there is a phase misalignment. Suppose that an output frequency ω1 is needed. From the upper right figure, we see that a control voltage V1 will be necessary to produce this output frequency. The phase detector can produce this V1 only by maintaining a phase offset φ0 at its input. In order to minimize the required phase offset or error, the PLL loop gain, KD KO, should be maximized, since

VCO

Razavi

Loop FilterThe output signal ud(t) of the PD consists of a DC component and a superimposed AC component. The latter is undesired; hence, it is canceled by the loop filter. In most cases, a first-order low-pass filter is used.

This network has a cutoff (3 dB) frequency ω1

= 1/RC. Thus, the filter transfer function is a simple low pass:

 

Lock RangeRange of input signal frequencies over which the loop remains locked once it has captured the input signal. This can be limited either by the phase detector or the VCO frequency range.

• Limited by PD: 0 < φ < π is the active range where lock can be maintained.

Ve-max = ± KD

π/2 When the phase detector output voltage is applied through the loop filter to the VCO,

Δωout – max = ± KV π/2 = ωL

(lock range)

where KV = KO

KD, the loop gain = product of the phase detector and VCO gains. This is the frequency range around the free running frequency that the loop can track.

• Doesn’t depend on the loop filter • Does depend on DC loop gain

• Limited by the tuning range of the VCO: Oscillator tuning range is limited by capacitance ratios or current ratios and is finite. In many cases, the VCO can set the maximum lock range.

Capture rangeRange of input frequencies around the VCO center frequency onto which the loop will lock when starting from an unlocked condition. Sometimes a frequency detector is added to the phase detector to assist in initial acquisition of lock.

Steady-state fosc(fi) characteristic of the basic PLL.

Problem 1.Determine the change in frequency for a voltage controlled oscillator (VCO) with a transfer function of KO = 2.5KHz/V and a DC input voltage change of ΔVO = 0.8V. Solution:

Δf = ΔVO KO Δf = (0.8 V)(2.5 kHz/V) = 2 kHz

Problem 2.Calculate the voltage at the output of a phase comparator with a transfer function of KD = 0.5V/rad and a phase error of ϴe = 0.75 rads. Solution:

VD = KD ϴe = (0.5 V/rad)(0.75 rad) = 0.375 V

Problem 3.Given fosc = 1.2 MHz at VCOin = 4.5 V and fosc = 380 kHz at VCOin = 1.6 Vthen Ko = (1.2 MHz – 380KHz) / (4.5V – 1.6V) rad/V = 283 krad/s/v

Examples

Problem 4.Determine the hold in range, (i.e. the maximum change in frequency) for a phase lock loop with an open loop gain of KV = 20kHz/rad.Solution:

Δfmax = KV π/2 = (20 krad) π/2 rad = 31.4 kHz

Problem 5.Find the phase error necessary to produce a VCO frequency shift of Δf = 10KHz for an open loop gain of KV = 40KHz/rad.Solution:

ϴe = Δf / KV = 10 kHz / 40 kHz/rad) = 0.25 rad

Example

Overall PLL systemFirst we will consider the PLL with feedback = 1; therefore, input and output frequencies are identical. The input and output phase should track one another, but there may be a fixed offset depending on the phase detector implementation.

 

We will start from the open loop gain, T(s).

T(s) = KDF(s)KO/s

F(s) is a simple LPF with a cutoff (3 dB) frequency ω1 = 1/RC.

Frequency and phase tracking loop

Then, T(s) becomes second order, Type 1:

 

It is sometimes useful to define a natural frequency, ωn, and a damping factor, ζ. This is standard control system terminology for a second order system. The key is to put the denominator of the closed loop transfer function, 1 + T(s), into a “standard” form:

either or

Taking the first formula, 1 + T(s) can be written as:

so, we can associate ωn and ζ with:

Frequency and phase tracking loop

A phase-locked loop has a center frequency of ω0 = 105 rad⁄s, KO = 103 rad/s per V, and KD = 1 V/rad. There is no other gain in the loop. Determine the overall transfer function H(s) for:a) The loop filter is F(s) = 1.b) The loop filter F(s) is shown below. 

ω1 = 1/RC

= 1/(120k x3.3nF) = 2525

Example

Consider a PLL with KO = 250 krad ⁄ s per V and that uses a Type I (XOR) phase detector KD = Vcc / π. The supply voltage is 5 V, and a simple RC filter (see below) is used. For the filter R = 120 kΩ and C = 3.3 nF. There is no other gain in the loop. a) Determine the transfer function H(s) = ϴo(s) ⁄ ϴi(s) of the loop.b) Calculate natural frequency ωn and damping ratio ζ. 

Example

Synthesizer PLL

We will now add the divider 1/N to the feedback path. This architecture is called an “integer-N” synthesizer.

We can calculate the loop gain, T(s):

• Loop gain is reduced by a factor of N. • In most applications, N is not constant, so KV

= KDKO is not a constant – varies with frequency according to the choice of N

Synthesize PLL

 

Phase-Locked Loop Based Clock GeneratorPLL perform:• Clock input division• Frequency MultiplicationIn this manner, the non integer frequencies can be developed.

fIN fOUT

fOUT = (fIN x N) / (R x P)

Example: fIN = 1000 Hz.

a) fOUT = 750 Hz

Pick: R = 1, N = 3, P = 4

b) fOUT = 350 Hz

Pick: R = 7, N = 7, P = 2

FM Demodulation

Four-modulus prescalersTo extend the upper frequency range of a frequency synthesizer but still allows the synthesis of lower frequencies. The solution is the four-modulus prescaler. The four-modulus prescaler is a logical extension of the dual-modulus prescaler. It offers four different scaling factors, and two control signals are required to select one of the four available scaling factors.

Integer-N Frequency Synthesizers with Prescalers cont.

Divider /R

fosc = 10MHz

Integer-N Frequency Synthesizers with Prescalers cont.As an example, the four-modulus prescaler can divide by factors of 100, 101, 110, and 111. By definition, it scales down by 100 when both control inputs are LOW. The internal logic of the four-modulus prescaler is designed so that the scaling factor is increased by 1 when one of the control signals is HIGH, or increased by 10 when the other control signal is HIGH. If both control signals are HIGH, the scaling factor is increased by 1 + 10 = 11.There are no longer two programmable /N counters in the system, but three: /N1, /N2, and /N3 dividers. The overall division ratio is given by:

Ntot = 100N1 + 10N2 + N3

In this equation N3 represents the units, N2 the tens, and N1 the hundreds ofthe division ratio Ntot. Here N2 and N3 must be in the range 0 to 9, and N1 must be at least as large as both N2 and N3 for the reasons explained in the previous example (N1,min = 9).The smallest realizable division ratio is consequently:

Ntot,min = 100 x 9 = 900 which is lower roughly by a factor of 10 than the previous example. For a reference frequency f1 of 10 kHz, the lowest frequency to be synthesized is therefore: 900 x f1 = 9 MHz.

Integer-N Frequency Synthesizers Examples

Numerical Example: We wish to generate a frequency that is 1023 times the reference frequency. The division ratio Ntot is thus 1023; hence N1 = 10, N2 = 2, and N3 = 3 are chosen. Furthermore, we assume that the /N1 counter has just stepped down to 0, so all three counters are now loaded to their preset values. Both outputs of the /N2 and /N3 counters are now HIGH, a condition that causes the four-modulus prescaler to divide initially by 111.

Solution: After N2 x 111 = 2 x 111 = 222 pulses generated by the VCO, the /N2 counter steps down to 0. Consequently, the prescaler will divide by 101. At this moment, the content of the /N3 counter is 3 – 2 = 1. After another 101 pulses (1 x 101) have been generated by the VCO, the /N3 counter also steps down to 0. The division ratio of the four-modulus prescaler is now 100.The content of the /N1 counter is now 7. After another 700 pulses (7 x 100) have been generated by the VCO, the /N1 counter also steps down to 0, and the cycle is repeated. To step through an entire cycle, the VCO had to produce a total of

Ntot = 2 x 111 + 1 x 101 + 7 x 100 = 1023 pulses, which is exactly the number desired.

The first CDR design required that the same clock used to serialize the data be sent to the receiver alongside the data. This method created some added problems for the receiver, as it had to deal with the jitter in the data stream and with the jitter in the clock stream, alongside the data stream. Another issue is the amount of data links is reduced by two using this system.

Clock Data Recovery

Differentiation CDR The steps taken by the algorithm to obtain the recovered data. The first plot is the input data, the second is the differentiated input data. We can see that the peaks occur at the zero crossings of the input data. The third plot is the fullwave rectified differentiated data. This data is used to create a clock, which is then used to create the fourth plot, the regenerated data

To counteract the effect of the system described earlier, a method utilizing two separate clock was developed. The transmitter serializes the data stream using the clock A. The cdr, at the receiver, uses information from a reference clock, clock B, located at the receiver end. To accomplish this operation a Phase-Locked Loop (PLL) is used.

Clock Data Recovery

INTRODUCTION OFTOUCH TECHNOLOGIES

EE174 – SJSU

TAN NGUYEN

Touch Technologies

• Introduction• Brief History• Market and Trends• Touchscreen Technology

• Resistive• Capacitive• Surface Acoustic Wave (SAW)• Infrared LED or Optical

• Touchscreen System• Applications

Introduction• An electronic visual display that locates the coordinates of a users touch within display area• Works independently of what is being displayed on screen• Allows a display to be used as an input device, removing the keyboard and/or the mouse as the primary input device for interacting with the display's content• Can be used without any intermediate device • Being used in a wide variety of applications to improve human-computer interaction.• Because of its convenience, touchscreen technology solutions has been applied more and more to industries, applications, products and services, such as modern smartphones, video games, kiosks, navigation systems, POS, tablets, etc. . .

Overall Touchscreen Market 2012-2017

Touchscreen Market 2007-2018 by Technology (Units)

Touchscreen Technology

There are four different technologies used to make touchscreens today: • Resistive• Capacitive (Surface and Projected Capacitive)• Surface Acoustic Wave (SAW)• Infrared LED or Optical

The Big Three of Touchscreen Technology

• Resistive Touchscreens are the most common touchscreen technology. They are used in high-traffic applications and are immune to water or other debris on the screen. Resistive touchscreens are usually the lowest cost touchscreen implementation. Because they react to pressure, they can be activated by a finger, gloved hand, stylus or other object like a credit card. • Surface Capacitive Touchscreens provide a much clearer display than the plastic cover typically used in a resistive touchscreen. In a surface capacitive display, sensors in the four corners of the display detect capacitance changes due to touch. These touchscreens can only be activated by a finger or other conductive object. • Projected Capacitive Touchscreens are the latest entry to the market. This technology also offers superior optical clarity, but it has significant advantages over surface capacitive screens. Projected capacitive sensors require no positional calibration and provide much higher positional accuracy. Projected capacitive touchscreens are also very exciting because they can detect multiple touches simultaneously.

Resistive Technology• Two layers of conductive material• Touch creates contact between resistive layers completing circuit• Voltage in circuit changes based on position• Controller determines location based on voltages• Any material can trigger sensors

Indium Tin Oxide (ITO)

Polyethylene (PET)

Types:• 4-wire (low cost, short life) is common in mobile devices• 5-wire (higher cost, long life) is common in stationary devices• 6-wire & 7-wire, 8-wire = replacement only

Constructions• Film (PET) + glass (previous illustration) is the most common• Film + film (used in some cellphones) can be made flexible• Glass + glass is the most durable; automotive is the primary use• Film + film + glass, others…

Analog Resistive

Analog Resistive

Size range• 1” to ~24” (>20” is rare)Controllers• Many sources• Single chip, embedded in chipset/CPU, or “universal” controller boardAdvantages• Works with finger, stylus or any non-sharp object• Lowest-cost touch technology• Widely available (it’s a commodity)• Easily sealable to IP65 or NEMA-4• Resistant to screen contaminants• Low power consumption

Analog ResistiveDisadvantages• Not durable (PET top surface is easily damaged)• Poor optical quality - The flexible top layer has only 75%-80% clarity• If the ITO layers are not uniform, the resistance will not vary linearly across the sensor. Measuring voltage to 10 or 12-bit precision is required, which is difficult in many environments. • No multi-touch• Require periodic calibration to realign the touch points with the underlying LCD image.

Applications• Mobile devices (shrinking)• Point of sale (POS) terminals• Automotive• Industrial• Wherever cost is #1

PET: Polyethylene Terephthalate

Surface Capacitive

The same phase voltage is imposed to the electrodes on the four corners, then a uniform electric field will be forming over the panel. When a finger touches on the panel, electrical current will flow from the four corners through the finger. Ratio of the electrical current flowing from the four corners will be measured to detect the touched point. The measured current value will be inversely proportional to the distance between the touched point and the four corners.

Advantages:• Surface capacitive technology is suitable for large size monitors.• Surface capacitive sensor can respond to light touch, and no pressure force is needed for detection• Visibility is high because structure is only one glass layer.• Surface capacitive is structurally tough as it is made of one sheet of glass.• Surface capacitive does not get affected by moist, dust, or grease.• Parallax is minimized in surface capacitive.• Surface capacitive has high resolution and high response speed.• Highly sensitive (very light touch)

Disadvantages:• Surface capacitive can detect touches by fingers only• nurface capacitive technology does not support multi-touch.• Surface capacitive touch screen is likely to be affected by noise. Recently, tolerance for noise has been improved with various methods such as noise shielding.

Surface Capacitive

Self-Projected Capacitive

● Uses rows and columns of conductors (overlayed in a grid pattern) ● One capacitor for each row and for each column ● A controller detects changes in capacitance for each row & column ● Controller determines an (x,y) coordinate based on the changes

Projected Capacitive

• Uses sensors to measure capacitance, when finger touches screen, capacitance increases• Typical Capacitor Values:

Cp ~ 15 pFCf ~ .5 pF

• Requires capacitance between object and sensor

Mutual Capacitance

• Uses an array of capacitors (located at each intersection of conductor grid)

Mutual Capacitance• Capable of recognizing multiple touches (Multitouch)

http://large.stanford.edu/courses/2012/ph250/lee2/docs/art6.pdf

Surface Acoustic Wave (SAW)• SAW touch screen consists of one glass

sheet with transmitting transducers, receiving transducers, and reflectors.

• Transmitting transducers generate ultrasonic waves that travel over the panel surface.

• The ultrasonic waves are reflected by the reflectors and received by the receiving transducers.

• SAWs are sent out from the transmitting transducers, and traveling along the edge of panel. The reflectors located on the edge of the panel change directions of the SAWs at the angle of 90 degrees, thus the SAWs travel over the panel.

Once the SAWs reached the other side of the panel, their directions get changed again by the reflectors located on the other side, and travel toward the receiving transducers. Once the SAWs are received by the receiving transducers, they will be converted into electric signals.

There are routes on which the SAWs travel from the transmitting transducers to the receiving transducers. Each route has its own distance. If one of the routes is touched by a finger, the pulse will be absorbed, and the SAW on the route will not be received by the receiving transducers. Thus, the sensor will recognize which route was touched, and locate the touched point.

Surface Acoustic Wave (SAW)

Advantages:• Visibility is excellent because it consists of one glass layer. • SAW touch screen is notable for its durability. Even though the panel surface gets scratched, its sensing function will not be affected.• It is relatively easy to build a large size touch screen in SAW technology.• SAW touch screen does not get affected by external electric noise.• Accuracy of detecting touched points does not get affected by environment nor passage of time. Thus, it is free of maintenance.• Resolution is relatively high.

Disadvantage:• The frame areas need to be wide because transducers are located.• Detecting function of SAW technology can be affected by water droplet, oil and so on. Malfunction can be caused by those factors.• SAW touch screen does not detect a touch by hard materials which do not absorb pulse.

Surface Acoustic Wave (SAW)

Surface Acoustic Wave (SAW)Size range• 6” to 52”Advantages• Visibility is excellent because it consists of one glass layer. • Finger, gloved hand & soft-stylus activation• Notable for its durability; can be vandal-proofed with tempered or CS glass• SAW touch screen does not get affected by external electric noise.• Accuracy of detecting touched points does not get affected by environment nor

passage of time. Thus, it is free of maintenance.

Disadvantages• Very sensitive to any surface contamination, including water• Relatively high activation force (50-80g typical)• Requires “soft” (sound-absorbing) touch object• Can be challenging to seal

• An infrared touchscreen uses a grid pattern of LEDs and light-detector photocells arranged on opposite sides of the screen. • The LEDs shine infrared light in front of the screen—a bit like an invisible spider's web. • If you touch the screen at a certain point, you interrupt two or more beams. A microchip inside the screen can calculate where you touched by seeing which beams you interrupted. Since you're interrupting a beam, infrared screens work just as well whether you use your finger or a stylus.

Traditional Infrared

Traditional InfraredVariations• Bare PCB vs. enclosed frame; frame width & profile height;no glass substrate; enhanced sunlight immunity; force-sensingSize range• 8” to 150”Controllers• Mostly proprietary, except IRTouch (China)Advantages• Scalable to very large sizes• Multi-touch capable (only 2 touches, and with some “ghost” points)• Can be activated with any IR-opaque object• High durability, optical performance and sealability• Doesn’t require a substrate

Disadvantages• Profile height (IR transceivers project above touch surface)• Bezel must be designed to include IR-transparent window• Sunlight immunity can be a problem in extreme environments• Surface obstruction or hover can cause a false touch• Low resolution• High costApplications• Large displays (digital signage)• POS (limited)• KiosksSuppliers• IRTouch Systems, Minato, Nexio, OneTouch, SMK, Neonode…• 10+ suppliers

Traditional Infrared

COMPONENTS OF TOUCHSCREEN

A basic touchscreen system has three main components:

• A touch screen.• A controller• Software driver.

The touchscreen is an input device, so it needs to be combined with a display and a PC or other device to make a complete touch input system.

Touch Screen

The touchscreen is the face of a touchsystem and the user's first contact point with the system. Its importance cannot be overstated, since it defines the quality and tactile feel of the touch system, and offers the only user interface. Key functional properties of the touchscreen are its optical transparency, its hardiness to wear and tear, and its touch accuracy. In all these areas, five-wire technology excels.

Controller• The controller - essentially the brain of the touch system - contains a microprocessor, analog-to-digital converters, and microchips to enable communication with the host PC. • The controller powers the touchscreen, controls the excitation, and interprets the information received from the touchscreen. • The controller filters the returning touchscreen data and converts it into raw touch coordinates, which are then sent to the PC by a digital software protocol. • A good controller will also perform substantial error-checking to detect abnormal or inconsistent touches and filter them out. • The controller determines what type of interface/connection you will need on the PC. Controllers are available that can connect to a Serial/COM port (PC) or to a USB port (PC or Macintosh). • Specialized controllers are also available that work with DVD players and other devices.

Software Driver

• The driver is a software update for the PC system that allows the touchscreen and computer to work together. • The driver software, residing on the host PC, is required to manage the raw coordinate data coming from the controller, apply calibration algorithms, position the mouse cursor, and generate mouse clicks. • Other important tasks include routines to define the video alignment parameters, and screening of incoming touch data for errors, inconsistencies, and integrity. • Good driver software will also offer diagnostic information in troubleshooting situations.

Touch Technologies by Size & Application

Touch Technologies by Materials & Process

Touch Is An Indirect Measurement