Intr. Mixed Signal

8/9/2019 Intr. Mixed Signal.

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VLSI (very large scale integration)

technology has moved many application

from analog to digital.

Analog & mixed mode VLSI design

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why Analog

Why analog circuit designers are in strongdemand today. Why?!!!

The physical world is in analog (at macroscopic level),

such as

The output signals of many signal sources are allin analog form, such as microphones, a

temperature sensors in automobile engines, and

the photo cells in digital cameras, are all in

analog form.


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The speakers in mobile phones and computer

monitors need analog input signal.

The RF signals in space and at the antenna arealso in analog.

some functions can not be replaced by

digital signal processing, such as analog-to-

digital and digital-to-analog conversion,

filtering, and so on.


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A mixed-signal integrated circuit is any

integrated circuit that has both analogcircuits and digital circuits on a single

semiconductor die.

Typically, mixed-signal chips perform

some whole function or sub-function in alarger assembly such as the radio

subsystem of a cell phone, or the read

data path and laser slide control logic of a

DVD player. They often contain an entire

system on a chip.


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Examples of mixed-signal integrated

circuits.

Data converters using delta sigma

modulation.

ADC/DAC using error detection,error

correction. Digital Radio chips.


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Analog signals versus Digital signals:

Signal: A signal will be considered to be any detectablevalue ofvoltage, current, orcharge. A signal should

convey information about the state orbehaviorof a

physical system.

Analog signal is a signal that is defined over a continuous

range of time and a continuous range of amplitudes.

Digital signal is a signal that is defined only at discrete

values of amplitude, or said another way, a digital signalis quantized to discrete values.


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Applications:

Communications: cell phones, personaldata assistants (PDA), wireless radios forbase-stations, routers, modems, wireless

sensor networks.

Consumer Electronics: audio, TV, video,digital cameras, automotive control, toys.

Measurement & Instrumentation:

medical equipment, lab bench equipment,semiconductor test equipment, scientificequipment.

Computing and Control: dataacquisition, storage media, sound cards.


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We need

Analog-to-digital converters (ADC) todigitize the input signal,

Digital-to-analog converters (DAC) to

reproduce the analog signal after digital

signal processing.

Analog pre-processing (before the ADC)

and post processing (after the DAC) are

needed, such asamplification, filtering, equalization.)


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Why is analog design challenging?

Digital circuits deal primarily with speedpower tradeoff.

Analog circuits deal with multi-

dimensional tradeoffof speed, power,

gain, precision, supply,

Due to speed and precision requirements,

analog circuits are much more sensitive

to noise, crosstalk, and otherinterferences.


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Analog circuits are much more sensitive to

second orderdevice effects High performance analog circuit design

can rarely be automated - typically require

hand-crafted design and layout. (digital

circuit design is mostly automated fromlogic synthesis to placement and routing).

Modeling and simulation of analog circuits

is still problematic, requiring experienceand intuition.


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Economic forces require the development

of analog circuits in mainstream digital

processes.

Economic forces pushing the integration

of analog and digital functions onto a

single substrate Many levels ofabstraction are required.


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CMOS technology is usually optimal for digital

performance and scaling, while bipolar

transistors are usually optimal for analogperformance, yet until the last decade it has

been difficult to either combine these cost-

effectively or to design both analog and digital in

a single technology without serious performancecompromises.

The advent of technologies like high

performance CMOS, BiCMOS, CMOS SOI and

SiGe have removed many of the compromisesthat previously had to be made.


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Why CMOS Mixed-Signal Integration?

Very large scale integration of both high-density

digital circuits (such as DSP and memory) andanalog circuits (including amplifiers, filters, and

A/D & D/A converters) for low cost.

Ideal properties ofMOS switches for high

accuracy sample-data circuits, such asswitched-capacitor filters and A/D & D/Aconverters.

Device scaling : new CMOS technologies withsmaller feature sizes (such as 0.25mm and0.18mm) can operate at increasingly high speed(5GHz), comparable to some bipolartechnologies.


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Bipolar tr. can operate at higher frequencies thanCMOS with relatively smaller power consumption.

Digital circuits in bipolar are power hungry, prohibitingvery large scale integration.

BiCMOS technologies have most advantages of bothCMOS and bipolar technologies but at the expense ofhigher manufacturing cost due to required extraprocessing steps.

Thus CMOS technologies become mainstreamtechnologies for mixed-signal integration due to theadvantages of low cost and high integration density.


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Why Integrated?


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Introduction and overview

Analog vs. digital signals

Mixed-signal circuits

Technology choice


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Analog signals vs. digital signals

Digital circuit design needs many transistors, tradeoffspeed-power and is very automated.

Analog circuit design doesnt need so many transistors,

but many tradeoffs (distortions, gain, power, speed, ...)

and skills. Circuit Analysis: the art of decomposition of a circuit

into manageable pieces; its based on enough accurate

models and it has one solution for one circuit.

Circuit Design: the art of synthesizing circuits based

on experience from extensive analysis; it can generate

many solutions for a set of specifications.

Design skills are best acquired through learning by

doing.


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God has created the world

analog

Man has created digital

world


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Intr. Mixed Signal