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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
06EC63
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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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NYQUISTRATE
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