1ISSUE 3

Field ProgrammableAnalog Arrays

Ultra Wide Band Integrated Optical RX

Japan EDA InsightResearch Inspiring

Innovation

FirstYear-Issue3-October2012

2 ISSUE 3

Visit VLSI Egypt Websitewww.vlsiegypt.com

Improve and Share Your Knowledgeeven more

1ISSUE 3

Stay Connected

Get tuned to our recent updates andactivities by following us at

VLSI Egypt Grouphttp://www.facebook.com/groups/VLSIEgy/

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2 ISSUE 3

A Magazine by VLSIEgypt

3

7

Editorial WordWelcome to VLSI Egypt magazine

Integrated Optical ReceiversResearch Inspiring InnovationThe next Big "Small Thing"

Field Programmable Analog ArraysA brief history

Why Do we need UWB?

1 0

1 2

1 6

23

Editorial Team

Mohamed Atef

Muhammad El-Khashab

Khaled Kabil

Website

www.vlsiegypt.com

2 ISSUE 3

The maturity and performance of standard CMOStechnologies make the optoelectronics integratedcircuits (OEIC) a competitive solution for manylow-cost consumer and sensor applications

Optical IntegratedReceivers7

VLSI-Egypt is a non-profit, service oriented,community based NGO

Contacts

magazine@vlsiegypt.com

Japan EDA InsightASIP Solutions

4

Ahmad Ibrahim

Editor in Chief

Ahmad Abou El-Saoud

Hussein Ali

26

3ISSUE 3

Editorial Word

4

1 8

Presenting the third issue of VLSI Egypt magazine is like a dream coming

true. The great feedback and interaction we had received from the

community has been overwhelming and has allowed us to continue and

sustain this activity and develop it even further.

First of all, we would like to thank all the authors who contributed and all

those who contacted us with feedback and offered their help. We would also

like to encourage any those interested in writing articles, whether they are

business, technical or educational, to contact the editorial group and we

would be more than happy to answer any ofyour inquiries.

This issue of VLSI Egypt covers a whole new set of topics in addition to the

continuation of previously initiated series. We continue our series on EDA

in Japan with the story behind the ASIP Meister design tool. The series on

current trends in RF and Microwave and IC research continues with a

discussion on why we need UWB. In this issue we give an overview about

the analog counterpart of FPGAs, that is Field Programmable “Analog”

Arrays (FPAAs) and its history. A historical overview of Arduino and its

evolution and a brief article on integrated optical receivers are also

presented. A discussion on the goals and objectives of research and how new

research associates with new business opportunities is presented through an

article discussing the research and motives of innovation. We also present a

detailed guide on Scholarships, Tuition and Graduate studies in the

European Union. This issue also contains the first articles written in Arabic

as opposite to all-English issues previously published.

We hope you find this issue ofVLSI Egypt interesting and useful. We would

also like to ask you to update us with all your feedback, opinions and

comments as this is how we asses our progress and success. Finally we

would like to thank you all very much for your interaction, support and for

keeping VLSI Egypt such a dynamic community.

Welcome to the Third Issue ofVLSIEgypt magazine

1 0

4 ISSUE 3

As we set in our first article, Japan EDA

Insight will focus on an Insight “small

piece of information” topics that vary

from the Educational System in Uni-

versities, Research Organizations,

Design Tools, Hardware Platforms, and

many other EDA trends, based on my

experience living and studying in Japan,

which I truly hope that VLSI-Egypt

magazine readers find useful and inter-

esting.

In this article I would present one of

most powerful tools in processor design

which my Prof. Masaharu Imai architec-

ted through years of effort and collabor-

ation from different lab members and

ended in a spin out as a commercial tool

known as ASIP Meister - An EDA tool

for drastically reducing the design time

of Application Specific Instruction Set

Processors (ASIP). I would mainly ref-

erence the company web site located at

http://www.asip-solu-

tions.com/en/asip_meister.html and

conference publications to introduce

this tool to VLSI-Egypt magazine read-

ers.

Different Processor Technologies

Processor technologies vary in their

customization for the problem at hand,

so assume that you have the functional-

ity described by the program in Figure

1 . You can typically design a processor

which exactly do this functionality and

nothing else (we call this Single Purpose

Processor – note the shape match), a

processor driving a baby bear toy hitting

a drum is one example. Or, you can

design a processor that executes the de-

sired functionality and extends this to

all problems with same nature, we call

them Application Specific Instruction

Set Processors (ASIPs), a Digital Signal

Processor (DSP), a Vide co-processor

and a Micro Controller are examples of

these kind of ASIPs. Or, you can design

a processor that executes any kind of

problem at hand (note again the shape)

and these are desktop/laptop processors

or what we call General Purpose pro-

cessors.

In depth, the main difference is in the

architecture of the computation engine

used to implement the desired func-

tionality. For a single purpose processor,

By: Mohamed AbdElSalam

JapanEDAInsight (2)

State of the Art

5ISSUE 3

as shown in Figure 1 , it contains only

the components needed to execute a

single program - you would find just

few registers and a fixed control logic

with a small data memory and no pro-

gram memory, its merits are speed, low

power and small die size. For an applic-

ation specific processor, you would have

an optimization for a particular class of

applications having common character-

istics as we stated, so you would find

more registers, a program memory with

Instruction Register (IR) and Program

Counter (PC), a separate Data/Program

memory and a custom Arithmetic, Lo-

gic, and Shift unit (ALU) with special

functional units that solve specific ap-

plication domain computations (signal

processing, multimedia, control ori-

ented). Its merits are more flexibility,

good performance, size and power. On

the other hands, the general purpose

processor has a general purpose data

path with large register file and general

ALU, it has programmability using a

Program/Data memory and IR/PC re-

gisters as ASIPs, its merits are high flex-

ibility and high computation power.

Now, after we have understood the main

concept behind an ASIP, let’s introduce

ASIP Meister (Master in German).

ASIP Meister generates dedicated pro-

Fig.1 Different Processor Technologies – A Simple View

Fig.2 ASIP Meister Design Flow

6 ISSUE 3

cessor hardware descriptions and soft-

ware development tools automatically

based on target processor specifications.

You can easily get high flexibility for

processor design only by modifying the

processor specifications on user friendly

ASIP Meister GUI.

Design Flow with ASIP Meister

Lets’ summarize, the design flow with

ASIP Meister (A Snapshot is shown in

Figure 3) is as follows:

1 . Set the design goals & architecture

parameters of the target ASIP, such as

the number of pipeline stages and in-

struction/data bit-width.

2. Select the hardware resources of the

ASIP from (Flexible Hardware Model)

FHM database library and set paramet-

ers for each resource.

3. Define ASIP storage specification &

I/O interface.

4. Define the instruction type, format

and exception information.

5. Check design quality with architec-

ture-level estimation.

6. Describe the behavior of each in-

struction using ANSI-C like syntax.

8. Describe the micro-operation of each

instruction per pipeline stage.

9. Check the performance with the gen-

erated HDL descriptions and software

development tools.

For more details, I would recommend to

go to Japanese site of ASIP Solutions

and use google translate (I see good

translation results! ! ! )

*References

Generation ofHDL Description

M. Itoh, S. Higaki, J. Sato, A. Shiomi, Y.

Takeuchi, A. Kitajima, M. Imai, “PEAS-

III: An ASIP Design Environment,”

2000 IEEE International Conference on

Computer Design: VLSI in Computers

& Processors, pp.430-436, September

2000.

Software Tools Generation

S. Kobayashi, Y. Takeuchi, A. Kitajima,

M. Imai, “Compiler Generation in

PEAS-III: an ASIP Development Sys-

tem,” Proc.

of SCOPES 2001 , March 2001 .

Lessons To Learn

In my opinion Japan’s, leading in em-

bedded systems since the early days lies

in the strong knowledge in (1) Processor

design – we have many companies

which developed their own processors

SH/SuperH family from Renesas, M32R

from Mitsubishi, etc. and still prefers to

use over ARM/Intel based processors

(2) Real Time Operating Systems –

ITRON is a national project that aims to

be in all embedded systems sold in Ja-

pan from vending machines (Jidohan-

baiki), automotives, etc. and its

evolution now lead to T-Kernel/T-En-

gine projects which are main corner-

stones in Ubiquitous Japan (3) FPGA

prototyping – as an economic way to

spread IP design culture among stu-

dents (4) Applying this knowledge in

commercial embedded systems on large

scale with government support to give

preference to indoor embedded systems.

Dr. Muhammad Abdel-Salam

Technical Lead,

Mentor Graphics Emulation Division

(MED)

Figure 3. ASIP Meister: An ASIP Design Environment

7ISSUE 3

Optical absorption in a semiconductor

material is the key-effect to convert op-

tical power into an electrical current.

This conversion is done by a photodiode

which is the first stage in any optical re-

ceiver. Discrete photodiodes can be

connected to transimpedance amplifier

(TIA) chip in multi-chip packages by

wire bonding or in heterogeneous integ-

rated circuits. The discrete solution per-

formance can be optimized separately

by using photodiode and TIA from dif-

ferent technologies. The high costs due

to complex production and assembly

process, and potential noise sources and

bandwidth reduction due to bonding

pads and package pins are the main

drawbacks.

An alternative low-cost solution in the

visible spectral range is the integration

of photodiodes with the TIA and post

amplifiers in standard CMOS and BiC-

MOS technologies. The maturity and

performance of standard CMOS tech-

nologies make the optoelectronics in-

tegrated circuits (OEIC) a competitive

solution for many low-cost consumer

and sensor applications. OEIC give a

better performance than discrete solu-

tions because there are no bonding

pads, no bond wires and no package pin

parasitics between photodiode and

amplifier input [1 ] .

Integrated PhotodiodeThe integrated photodiode is the main

component and the first stage in the in-

tegrated optical receiver. The photodi-

ode converts the optical power into an

electrical current. The photodiode

should convert photons into charge

carrier pairs with maximum efficiency

and to transport them to the electrodes

as fast as possible. Also the capacitance

of the photodiode must be as low as

possible to keep the high frequency loss

of the photocurrent low to reach highest

possible sensitivity. These demands are

partially conflicting. So a trade-off is

necessary, especially due to the

wavelength dependence of the penetra-

tion depth. More details about the the-

ory of integrated photodiodes can be

found in [2, 3] .

Depending on the specific application,

the thickness of the intrinsic zone of the

photodiode must be optimized; Figure 1

Figure 1 PIN Photodiode structure

By: Mohamed Atef

Integrated Optical Receivers

8 ISSUE 3

shows the structure of a PIN photodi-

ode. For a good trade-off, the main

parameters that must be known are the

maximum data rate, the operating

wavelength, type of photodiode and the

maximum voltage available for the pho-

todiode. A main characteristic of integ-

rated optical receivers is the achievable

sensitivity, which depends strongly on

the responsivity of the photodiode and

also the capacitance, so minimum capa-

citance and maximum responsivity lead

to maximum sensitivity. This could be

achieved by increasing the thickness of

the intrinsic layer. But this contradicts

to speed, since increasing the intrinsic

layer thickness without increasing the

reverse voltage would lead to a double

penalty (quadratic dependence) since

the electric field decreases and so the

speed of the charge carriers decreases.

Additionally the distance the charge

carriers have to drift increases and so

the whole transition time of the charge

carriers increases dramatically. To solve

this problem partially the voltage across

the diode has to be increased according

to the increase of the thickness of the in-

trinsic layer. The main goal is that the

electric field is at a high constant level

where the charge carriers travel with

saturation drift velocity. In practice,

however, the saturation velocity is not

achieved in most cases due to limited

available supply voltage.

Often a certain data rate is given, so the

photodiode has to achieve a certain rise-

and fall-time. In a first order approxim-

ation the necessary 10%-90% rise- and

fall-time of the photodiode can be cal-

culated from the formula (1) with td as

the drift time through the intrinsic zone.

(1 )

When rise- and fall-time are nearly

equal, then the formula (1) simplifies to

formula (2) and gives approximately the

drift-time of the charge carriers through

the drift zone. In both cases the factor 3

indicates a conservative approximation

and for an aggressive approximation the

factor can be two.

(2)

The cut-off frequency of the PIN-pho-

todiode can be estimated by:

(3)

Under the assumption that the drift ve-

locity reaches saturation (vs=107cm/s)

the maximum allowable thickness of the

intrinsic layer can easily be calculated

by:

(4)

The necessary voltage for the PIN-diode

can now also be calculated with the

electric field where saturation occurs.

(5)

Transimpedance Amplifier

Photodiodes do not use any amplifica-

tion effect and have responsivity (ratio

of output current to input light intens-

ity) that is for example ≤ 0.5A/W for a

silicon photodiode at a light wavelength

of 650nm. Therefore a combination of a

photodiode with an amplifier is neces-

sary in all practical applications. In op-

tical receivers current-to-voltage

converters are necessary in order to

convert the photocurrent delivered by

the photodiode into an output voltage

which is proportional to the input cur-

rent. The transimpedance amplifier is

the most suitable preamplifier config-

uration used in optoelectronic receivers.

For most optical receiver applications

these amplifiers need a high and also

variable gain, high bandwidth, low noise

and low input impedance. The main

characteristics of transimpedance amp-

lifiers are discussed in [3] .

The preamplifier is used to convert the

incoming photocurrent into an output

voltage, which is amplified by the fol-

lowing stages. The simplest way to do

this conversion is a resistor between the

PD output and the supply voltage as

shown in Figure 2. The preamplifier is

one of the determining parts concerning

the sensitivity and bandwidth of an op-

tical receiver. The sensitivity mainly de-

pends on the responsivity of the PD and

the input referred noise current of the

circuit. Due to the fact that the output

current of the PD is the smallest signal

in the circuit, this point is the most

sensitive concerning noise. The signal-

to-noise ratio is most critical at the in-

put node of the preamplifier. Therefore,

the noise of the preamplifier is the

dominating part of the input referred

Figure 2 Simplest possibility of the

preamplifier

9ISSUE 3

noise current. Again the noise of the

resistor R and the first amplifying stage

are the deciding factors.

The most interesting characteristics of

the preamplifier, therefore, are the

bandwidth and the input referred noise

of the circuit. For the simple receiver

shown in Figure 2 the bandwidth is in-

directly related to the capacitance of the

input node and the resistor R. In this

simple model, the capacitance of the in-

put node consists of the capacitance of

the PD, and the input capacitance of the

amplifier. To achieve a high bandwidth

therefore the resistance R has to be

small, as well as the capacitance of the

input node.

The noise of the circuit shown in Figure

2 depends also on the resistor R, the ca-

pacitance of the input node and the first

amplifier stage of the following amplifi-

er. To achieve high bandwidth the res-

istor R must be small and therefore its

noise current dominates the sensitivity

of the optical receiver. With a more

complicated circuit, for example a TIA,

a better performance can be achieved.

Shunt­Shunt Feedback TIAFigure 3 shows the basic circuit of a

shunt feedback TIA as a preamplifier. In

the TIA circuit CT consists of the capa-

citance of the PD and the input capacit-

ance of the TIA.

Let us compare the small-signal transfer

functions of the two structures in Figure

2 and Figure 3, which is the transim-

pedance gain vo/iin.

From Figure 2

(6)

From Figure 3

(7)

The DC transimpedance gain for the

simple TIA in Figure 2 is the transim-

pedance resistor value Rfb. For high

amplifier gains A0 this is also the case

for Figure 3. Comparing the frequency

behavior, the dominant pole which

defines the small-signal bandwidth for

the two circuits are defined by:

From Figure 2

(8)

From Figure 3

(9)

Equation (8) shows, that the bandwidth

of the simple resistor TIA is completely

defined by a given transimpedance and

photodiode capacitance. Equation (9)

shows that the shunt-shunt feedback

TIA has an approximately A0 times

higher bandwidth compared to a simple

resistor TIA. The amplifier gain A0 is

design dependent and higher than 1 for

frequencies up to the amplifier’s transit

frequency ft. Therefore the increased

bandwidth for the same transimpedance

value is one of the most important ad-

vantages of a shunt-shunt feedback TIA

compared to a simple resistor solution.

The advantage of a shunt-shunt feed-

back TIA compared to the simple circuit

described before is the fact that the

bandwidth is indirectly related to the

resistor Rfb divided by the open-loop

gain A0 of the TIA (Rfb/A0). Therefore

the noise can be decreased for a given

bandwidth, because of a large resistor

RF. The smaller CT and the larger Rfb,

the higher the sensitivity is for a given

responsivity (more discussion will be

presented in the next articles). For a

high bandwidth it is important to have

small CT and small Rfb. CT is domin-

ated by the PD capacitance, a trade-off

between sensitivity and bandwidth has

to be found for the feedback resistor.

[1 ] M. Atef and H. Zimmermann,

“10Gbit/s 2mW Inductorless Transim-

pedance Amplifier “, IEEE International

Symposium on Circuits and Systems

(ISCAS), 2012.

[2]H. Zimmermann, Integrated Silicon

Optoelectronics, Springer, 2000.

[3]H. Zimmermann and K. Schneider,

Highly Sensitive Optical Receivers,

Springer, 2006.

Dr. Mohamed Atef

Assistant Prof. Electrical Eng. Dept. ,

Assiut Univerity, Egypt.

moh_atef@au.edu.eg

Figure 3 Basic circuit of a TIA as

preamplifier

10 ISSUE 3

Research Inspiring Innovation,the next Big “Small Thing”

Our ancestors achieved great accom-

plishments in architecture, medicine,

astronomy, etc. we can’t achieve any-

thing unless we searched the heritage

they left for us and learn from them.

However; Research isn’t information

gathering or transferring of facts from

books and magazines where no contri-

bution to new knowledge is added. Re-

search is defined as “a systematic

process of collecting and analyzing in-

formation (data) in order to increase

our understanding of the phenomena

about which we are concerned”. It is

cyclic and should be nonstop process. It

starts with a very defined and specific

question resulting into the most suitable

conclusion for your problem based on

the researcher hypotheses and passing

through systematic steps. Research is

about curiosity and questioning what

people see normal, closely observe de-

tails, and experiments to gain new

knowledge. Research is for solving ex-

isting problems and also for developing

the current state of any process.

"Discovery consists of seeing what every-

body has seen and thinking what nobody

has thought. "

— Albert von Szent-Gyorgy

The Question now “Is Research only a

Scientists Job?” .Definitely the answer is

“No”. We are all in certain degree re-

searchers by nature but we never no-

ticed! When you want to travel to the

coast and compare between different

transportation means: whether car and

Plane or bus for different tradeoffs:

speed, cost and safety. So there is an ob-

jective and by collecting data, analyzing

it to reach the most suitable way for you

to travel. Another example is when you

are assigned to a college or work project.

You start by defining the problem, col-

lecting data from different sources,

analyzing what you gathered till reach-

ing the solution.

Another Question arises “What to do

after Research and reaching my conclu-

sion? Is Research an objective itself?

By Mohamed Farag Hassan

11ISSUE 3

”.Here comes the secret of this article,

The Innovation part; Innovation should

be targeted to integrate the Researching

Process, complete the big picture and

produce solutions and new applications

in a creative way. Innovation is the abil-

ity to see Research Problem as an op-

portunity - not a threat. It’s about

designing and using this original fact

you came up with your Research Con-

clusion in a useful way hence becomes a

business potential or a promising star-

tup! !

"Capital isn't so important in business.

Experience isn't so important. You can

get both these things. What is important

is ideas. If you have ideas, you have the

main asset you need, and there isn't any

limit to what you can do with your busi-

ness and your life."

— Harvey Firestone

Getting great ideas is a fantastic ap-

proach but are they applicable? Will

they help in solving the problem? We

are researching to produce a new

product, service or solve an existing

problem while using creative and new

ideas .Here the cycle would be complete.

Research is the fuel of innovation, it

provides us with all information and

data we need to come up with creative

ideas. Also innovation keeps continuous

feedback to researchers, where they

should research and what new problems

they should face. Research provides the

ground to have a lot of ideas so you can

have a good idea then you will find your

“EUREKA” moments through innova-

tion. We all know what happened with

Amazon and their success story when

they changed from selling books to

selling everything from A to Z online.

Also Intel is another good example. Intel

was the leader of microprocessors’ tech-

nologies and architectures over the past

30 years .Now; they have expanded their

domain to include software products.

Amazon and Intel didn’t depend on

technical and market Research only, or

Innovation and creative Ideas only, but

both of them to integrate their cycle of

success.

"Innovation— any new idea—by defini-

tion will not be accepted at first. It takes

repeated attempts, endless demonstra-

tions, monotonous rehearsals before in-

novation can be accepted and

internalized by an organization. This re-

quires courageous patience."

— Warren Bennis

Research Inspiring Innovation is how do

we intend to win in business and the

reason for the existence ofmost success-

ful startup’s and big companies .Let's

make it our culture to research and in-

novate...let's expand our F R O N T I E

R S.

Muhammad Farag Hassan

PastChair, IEEE AinShams Univ. Stu-

dent Branch.

mo.farag2012@ieee.org

12 ISSUE 3

Field Programmable AnalogArrays, A Brief History

IntroductionSensor-readout interfaces and filters in

transceiver front-ends for wireless com-

munication are implemented in the ana-

log domain. Although analog circuits

are very complicated and hard to

design, they are very power efficient.

For this reason, analog circuits are suit-

able for mobile applications. Usually,

these analog circuits are application

specific integrated circuits (ASICs).

Due to the rapid change of communica-

tion standards, ASICs re-designing and

development are very expensive. There-

fore, there is an increasing need of re-

configurable analog circuits. Field

programmable analog array (FPAA) is

the solution.

FPAAs are flexible integrated devices

containing several configurable analog

blocks (CABs) and signal routing net-

work between them. By programming

the CABs and changing the connections

between them, various analog functions

could be implemented. The main pur-

pose of FPAAs is the rapid-prototyping

of analog circuits like there digital coun-

terpart the field programmable gate ar-

ray (FPGA). Unlike FPGAs, FPAAs are

more application driven than being a

general purpose; this is because analog

circuits are more complex, non-linear,

noisy and difficult to design than digital

circuits.

In conclusion, the main purpose of

designing FPAAs is the need of adaptive

analog circuits in low power analog

front-ends. Moreover, FPAAs are

needed for rapid-prototyping of analog

circuitry to ensure the correct function-

ality of mixed signal system where sim-

ulations are not enough.

HistorySince the term was first used in 1991 by

Lee and Gulak [1 ] , the FPAA shown in

Figure 1 has become an interesting

widely research topic. It was introduced

to describe the basic idea ofCABs which

can be connected by a routing network,

and are configured digitally. The idea

was further enhanced by the same au-

thors in 1992 and 1995 [2, 3] where op-

amps, capacitors, and resistors can be

connected to form a biquad, for in-

stance. The chip was manufactured in a

1 .2µm CMOS technology, and operates

in the 20kHz range at a power con-

sumption of 80 mW.

In 1995, a similar idea, the electronic-

ally-programmable analog circuit

(EPAC) was presented by Pierzchala et

al. [4] . Although their test chip featured

By: Mohamed F. Hassan

Technical

13ISSUE 3

only a single integrator, they nonethe-

less proposed the concept of a local in-

terconnect architecture to avoid the

bandwidth limiting switches in a rout-

ing network, and the design was com-

mercialized.

A successful commercial FPAA supplier

is Anadigm [5] whose products allow

simple instantiations of complex filters,

but the switched capacitor (SC) tech-

nique limits their bandwidth to 2 MHz

In 2002, a continuous-time (CT) FPAA

using programmable operational

transconductance amplifiers (OTAs)

and programmable capacitor arrays was

presented by Pankiewicz et al. [6] that

functioned in the 1MHz range. The

FPAA was designed in a chessboard lay-

out shown in Figure 2 with local inter-

connects and switches and the OTA

tuning is achieved by a programmable

current mirror. This technique allows

Gm tuning with 5-bit precision which is

limited by the large chip area each addi-

tional bit of precision adds. Therefore,

this technique is not feasible for high

precision tuning in an FPAA due to the

chip area it would require.

Also in 2002, the reconfigurable analog

signal processor (RASP) shown in Fig-

ure 3 was presented by Hall et al. [7] . In

2005, a second version of the RASP fol-

lowed [8] . Both implement a classic lay-

out with CABs connected with a global

routing network. Floating gates are used

as switches in the routing network and

in tuning the active elements. The

design attempts to achieve the com-

plexity and flexibility similar to that of

FPGAs by incorporating high-level ele-

ments such as second order bandpass

filters and four-by-four vector-matrix

multipliers into its CABs. This makes

interesting applications easily possible

such as Fourier analysis, but degrades its

frequency performance. The 0.35 µm

CMOS technology used and the neces-

sary large routing network - which in-

troduces many bandwidth-limiting

switches into the signal path - limit its

frequency range to around 100 kHz.

The programming of the floating gates

is controlled externally by a PCB con-

taining an FPGA and analog switches;

the chip itself is not able of independent

reconfiguration.

In 2007, the above group introduced a

specialized version of the RASP [9] . The

complex CABs are all replaced by sim-

pler CABs each containing just one

second-order biquad tunable by floating

gates shown in Figure 4. They are still

connected by a classic global routing

network using floating gate switches.

The maximum achievable bandwidth is

improved to around 10-15MHz on the

expense of its reduced complexity and

Figure 1 FPAA system architecture by

Lee and Gulak [1]

Figure 2 Schematic of chessboard

connection scheme by pierzchala [6]

Figure 3 FPAA architecture ofRASP

14 ISSUE 3

application range. The OTAs are oper-

ated in sub-threshold region by floating

gates.

In parallel with the above work, the par-

allel connection of OTAs (Figure 5) to

achieve tuning was proposed by Pavan

and Tsividis [10] in 2000. The overall

transconductance of the amplifier de-

pends linearly on the number of OTAs

switched on. This allows wide range

tuning without the usual drawbacks, e.g.

low dynamic range at low frequency set-

tings. This technique was taken up and

developed by Joachim Becker in 2004

[11 ] when he proposed its use in a

hexagonal local interconnect architec-

ture.

It does not require a routing network

and eliminates switching in the signal

path which improves the frequency re-

sponse. Instead, the tunable Gm cell

consisting of parallel connected OTAs is

used to implement the required Gm-C

stages and to implement the routing at

the same time. By simply switching all

of the cells parallel connected OTAs off,

a signal path is cut off. The arrangement

of the cells in a hexagonal lattice as

shown in Figure 6 allows the instanti-

ations of filters of all orders. By doub-

ling the OTAs in a tunable Gm cell, and

connecting half of them with inverted

output terminals, the signal can be

transconducted either direct or inverted,

depending on which set of OTAs is

switched on.

In 2005, Fabian Henrici joined the work

group and developed a novel switchable

and invertible OTA which cut the num-

ber of OTAs in a tunable Gm cell by

half, thus reducing parasitic capacit-

ances and nearly doubling the maxim-

um FPAA bandwidth. Together with

Joachim Becker, he developed an FPAA

using his OTA and the local intercon-

nect architecture introduced by Becker.

This collaboration resulted in the first

manufactured and published FPAA in

0.13µm CMOS technology, which was

presented at ISSCC (International Solid

States Conference) in 2008 [12] .

Moreover, Henrici continued on this

Fig.4 FPAA based on biquad tunable by floating gates [9]

Figure 5 Parallel OTA connection proposed by Pavan at el.

15ISSUE 3

work and manufactured an FPAA chip

in 0.13µm CMOS technology with con-

tinuous tuning through floating gates.

References

1 . Lee, E.K.F. and Gulak, P.G., “A CMOS

Field-programmable analog array," Sol-

id-State Circuits, IEEE Journal of, vol.

26, pp. 1860-1867, Dec 1991 .

2. Lee, E.K.F. and Gulak, P.G., “Field

programmable analogue array based on

MOSFET transconductors," Electronics

Letters, vol. 28, pp. 28-29, Jan. 1992.

3. Lee, E.K.F. and Gulak, P.G.,“A

transconductor-based field program-

mable analog array," in Solid-State Cir-

cuits Conference, 1995. Digest of

Technical Papers. 42nd ISSCC, 1995

IEEE International, pp. 198-199, 366,

Feb 1995.

4. Pierzchala, E. and Perkowski, M.A.

and Van Halen, P. and Schaumann, R.,

“Current Mode amplifier/integrator for

field programmable analog array " in

Solid State Circuits Conference, 1995.

Digest of Technical Papers. 42nd ISSCC,

1995 IEEE International, pp. 196-197,

Feb 1995.

5. Anadigm: Supplier of Dynamically

Programmable Analog Signal Pro-

cessors (dpASP), USA. ht-

tp://www.anadigm.com.

6. Pankiewicz, B. and Wojcikowski, M.

and Szczepanski, S. and Yichuang

Sun,“A field programmable analog array

for CMOS continuous-time OTA-C fil-

ter applications," Solid-State Circuits,

IEEE Journal of, vol. 37, pp. 125-136,

Feb 2002.

7. Hall, Tyson S. and Hasler, Paul and

Anderson, David V., “Field Program-

mable Analog Arrays: A Floating-Gate

Approach," in FPL '02: Proceedings of

the Reconfigurable Computing Is Going

Mainstream, 12th International Confer-

ence on Field Programmable Logic and

Applications, (London, UK), pp. 424-

433, Springer-Verlag, 2002.

8. Hall, T.S. and Twigg, C.M. and Gray,

J.D. and Hasler, P. and Anderson, D.V.,

“Large scale field programmable analog

arrays for analog signal processing,"

Circuits and Systems I: Regular Papers,

IEEE Transactions on, vol. 52, pp. 2298-

2307, Nov. 2005.

9. Hasler, P.E. and Twigg, C.M.,“An

OTA-based Large-Scale Field Program-

mable Analog Array (FPAA) for faster

On-Chip Communication and Compu-

tation," in Circuits and Systems, 2007.

ISCAS 2007. IEEE International Sym-

posium on, pp. 177-180, May 2007.

10. Pavan, Shanthi and Tsividis, Yannis,

“High frequency continuous time filters

in digital CMOS processes. Norwell,

MA, USA: Kluwer Academic Publish-

ers, 2000. See pp. 12, 13, 28, 141 .

11 . Becker, J. and Manoli, Y.,“A continu-

ous-time field programmable analog

array (FPAA) consisting of digitally re-

configurable GM-cells," in Circuits and

Systems, 2004. ISCAS '04. Proceedings

of the 2004 International Symposium

on, vol. 1 , pp. I-1092-5 Vol.1 , May 2004.

12. Becker, J. and Henrici, F. and

Trendelenburg, S. and Ortmanns, M.

and Manoli, Y.,“A Continuous-Time

Hexagonal Field-Programmable Analog

Array in 0.13 µm CMOS with 186MHz

GBW," in Solid-State Circuits Confer-

ence, 2008. ISSCC 2008. Digest of Tech-

nical Papers. IEEE International, pp.

70-596, Feb. 2008.

Mohamed F. Hassan

PhD student, Project Assistant; Electro-

dynamics, Microwave and Circuit En-

gineering; Vienna University of

Technology

Figure 6 Hexagonal FPAA structure

16 ISSUE 3

Since the release by the Federal Communications Commission (FCC) of a bandwidth of 7.5GHz (from

3.1GHz to 10.6GHz) for Ultra-wideband (UWB) wireless communications, UWB is rapidly advancing as a

short range high speed high data rate wireless communication technology. A new technology has been

employed into our daily lives with minimal interference known as the ultra-wideband or UWB. This

technology is an unlicensed service that can be used anywhere, anytime, by anyone. UWB which is well

known for its use in ground penetrating radar (GPR) has shown interest in communications and radar

applications. Unlike traditional systems, this can only operate over a specific range of frequencies. UWB

devices operate by employing a series of very short electrical pulses (billionths of a second long) that result

in very wideband transmission bandwidths. In addition, UWB signals can run at high speed and low power

levels. All these unique features ofUWB technology make it suitable for many different applications such as

positioning, geo-location, localization (accurate positioning, high multipath environments and obscured

environments), radar/sensor applications (vehicular, marine, GPR, imaging, wall-imaging, sense-through-

the-wall (STTW), surveillance systems), communications (high multipath environments, short range

communications, high data rates).

Why do we needUltra-wideband? (1)

Current Trends in RF and Microwave Integrated Circuits Research

By: Osama Haraz

State of the Art

17ISSUE 3

UWB TechnologyCurrently, there is an increased interest

in Ultra-wideband (UWB) technology

for use in several present and future ap-

plications. UWB technology received a

major boost especially in 2002 since the

US Federal Communication Commis-

sion (FCC) permitted the authorization

of using the unlicensed frequency band

starting from 3.1 to 10.6 GHz for com-

mercial communication applications

[1 ] . Although existing third-generation

(3G) communication technology can

provide us with many wide services

such as fast internet access, video tele-

phony, enhanced video/music download

as well as digital voice services, UWB

–as a new technology– is very prom-

ising for many reasons.

Large BandwidthThe FCC allocated an absolute band-

width more than 500 MHz up to 7.5

GHz which is about 20% up to 110%

fractional bandwidth of the center fre-

quency. This large bandwidth spectrum

is available for high data rate commu-

nications as well as radar and safety ap-

plications to operate in. Fig. 1 shows the

comparison between conventional nar-

rowband (NB) versus UWB communic-

ations in both time- and

frequency-domains. The conventional

NB radio systems use NB signals which

are sinusoidal waveforms with a very

narrow frequency spectrum in both

transmission and reception. Unlike a

NB system, an Ultra-wideband radio

system can transmit and receive very

short duration pulses. These pulses are

considered UWB signals because they

have very narrow time duration with

very large instantaneous bandwidth [2] .

Very Short Duration PulsesA typical received UWB pulse shape

which is known as a Gaussian doublet is

shown in Fig. 2(a). This pulse is often

used in UWB systems because its shape

is easily generated. Ultra-wideband

pulses are typically of nanoseconds or

picoseconds order. This is the origin of

the name Gaussian pulse, monocycle or

doublet. Transmitting the pulses directly

to the antennas results in the pulses be-

ing filtered due to the properties of the

antennas. This filtering operation can be

modeled as a derivative operation. The

same effect occurs at the receive an-

tenna. The spectrum of the Gaussian

doublet is shown in Fig. 2(b). Due to

using UWB systems those very short

duration pulses, they are often charac-

terized as multipath immune or mul-

tipath resistant.

Fig. 1 Time- and frequency-domain behaviors for narrowband versus UWB

communications [3] .

Fig. 2 (a) Idealized received UWB pulse shape[4] (b) idealized spectrum ofa single received UWB pulse [4]

18 ISSUE 3

High Data Rates with Fast Speed

The huge bandwidths for UWB systems

−compared to other conventional NB

systems− can show a number of import-

ant advantages. There is an increasing

demand for high speed and high data

rate applications in communication sys-

tems [5] . One of those advantages of

UWB transmission for communications

is the ability of UWB system to achieve

high data rates in future wireless com-

munications which require increasing

the bandwidth of the communication

system. While current chipsets are con-

tinually being improved, most UWB

communication applications are target-

ing the range of 100 Mbps to 500 Mbps

[6] . Table 1 shows the spatial and spec-

tral capacity for different communica-

tion systems such as UWB, wireless

local area network (WLAN) and

Bluetooth. The speeds of data transmis-

sion for different communication sys-

tems are summarized in Table 2. Using

UWB technology will enable us to

achieve higher data rates with higher

spatial capacity compared to other ex-

isting systems. In addition, UWB tech-

nology achieves very high speed for data

transmission. Another advantage of

UWB systems is the ability to effectively

reduce fading and interference problems

in different wireless propagation chan-

nel environments because of the limited

transmitted power of UWB systems [7] .

This is in addition to exploiting mul-

tipath or frequency diversity because of

the huge bandwidth of UWB systems

[8] . The signal-to-noise ratio (SNR) of

the UWB system can be increased using

some techniques such as antenna di-

versity and beamforming which in turn

will provide range extension and boost

the capacity of worldwide interoperabil-

ity for microwave access (WiMAX) for

wireless metropolitan area networks

(WMAN), and wireless fidelity (Wi-Fi)

for wireless local area networks

(WLAN) [9] .

Some Basic Definitions

C =B log(1+S⁄N)

C is the maximum channel capacity

B is the channel bandwidth

S⁄N is the signal-to-noise ratio (SNR)

of the channel

Low Power ConsumptionThe UWB technology has another ad-

vantage from the power consumption

point of view. Due to spreading the en-

ergy of the UWB signals over a large

frequency band, the maximum power

available to the antenna –as part of

UWB system– will be as small as in or-

der of 0.5mW according to the FCC

spectral mask shown in Fig. 3.This

power is considered to be a small value

and it is actually very close to the noise

floor compared to what is currently

used in different radio communication

systems [2] . Table 3 shows the power

spectral density (PSD) of some wireless

broadcast and communication systems

such as UWB, radio, television, 2G cel-

lular and WLAN. The PSD is defined as

the total transmitted power over the

operating bandwidth.

According to the definition in [10] , one

important feature of a radar and com-

munications transmitter is called the

effective isotropic radiated power (EI-

RP) which can be defined as the

product of its gain and input power. Fig.

4 shows the FCC spectral mask of the

indoor UWB EIRP emission level. It can

be seen that the maximum signal power

is limited to−41 .3 dBm per MHz

throughout the whole UWB frequency

range from 3.1 to 10.6 GHz. All the

Table 1 Spatial and spectral capacity for different communication systems

Table 2 Speed ofdata transmission for different communication systems

19ISSUE 3

UWB systems and devices must work

within this spectral mask for legal oper-

ation in order to comply with the FCC

standards and regulations.

Small Size and Low CostThe small size of UWB transmitters is a

requirement for inclusion in today’s

consumer electronics. The main argu-

ments for the small size of UWB trans-

mitters and receivers are due to the

reduction of passive components.

However, antenna size and shape are

other factors that need to be considered.

Ultra-wideband antennas are con-

sidered in the next article. Among the

most important advantages of UWB

technology are those of low system

complexity and low cost. Ultra-wide-

band systems can be made nearly “all-

digital”, with minimal radio frequency

(RF) or microwave electronics. The low

component count leads to reduced cost,

and smaller chip sizes invariably lead to

low-cost systems. The simplest UWB

transmitter could be assumed to be a

pulse generator, a timing circuit, and an

antenna.

Dr. Osama Haraz,

Concordia University, Montreal, Canada

Fig. 3 UWB versus other radio communication systems [3] .

Table 3 PSD of some wireless broadcast and communication systems

Fig. 4 FCC spectral mask for indoor UWB systems [1]

20 ISSUE 3

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26 ISSUE 3

Technical

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