ANALOG IC DESIGN INTRODUCTION
What is Analog IC Design? • Analog IC design is the successful implementation of analog circuits and systems using integrated circuit technology. • Circuits process signals continuous in time and continuous in amplitude
The (electronic) world is going Digital, • why Analog?
NEED • While many applications have replaced much analog circuitry with their digital counterparts, the need for analog circuit design is actually growing. • REASON------- • Consumer-focused electronics have become the driving force of industry, • But , consumer electronics has become all-digital, networked, sophisticated, and almost independent of time, place, physical embodiment, and content. Users expect their tailored audio and video content when, where, and how they want it, to their own schedule and convenience.
Ans.---As the digital demands have increased, they have increased the demands on analog as well, which is good for R&D and production investment. Ironically, new requirements for features in digital cell phones are dictating the needs for new analog functions. • And in turn, the increased analog capability has enabled more the desired digital functionality and performance, as well. • So we have one of the few cases where a positive feedback loop is for good • Example---Electronic application in demand • CELL PHONE
Basic Digital Handset • The key components of a basic handset are the radio, the power management, and the analog and digital baseband processing.
Analog in digital handset. • Interesting fact: There's more analog in a digital handset than in an analog model
In a digital handset, • --convert the voice signal to a digital stream (with an "analog" ADC). • ---But before conversion, need to filter it (using an analog filter). • --What comes out to your ear must be converted from digital to analog.(DAC) • --And there's an analog filter there to clean up that signal. • Getting the signal up onto the RF carrier, • ---power amplifier (PA), • --analog circuitry is needed to control the PA to ramp it up and down, and to control the power,
Putting the signal up on the air waves generally requires turning bits into a modulated carrier, which requires DACs and some filters (more analog parts). • On the receive side, what comes down from the RF carrier is a modulated signal that needs ADCs to decompose the signal into quadrature components.
The battery and power management CIRCUIT that's needed to handle all the new digital "stuff“ that's being packed into the newer models, like things to manage a color display, and the backlighting for it, high-performance audio, and so on.
Higher resolution camera---analog image processing required to interface a multi-megapixel camera sensor to the digital processor, • Music-player phones with iPod-like capabilities----high-quality playback digital-to-analog converters (DACs) and headphone driver amplifiers for audio playback. • TV reception is a new feature emerging in cell phones----keeping the display brightly lit to watch a video clip without consuming too much power requires power management. power-management and battery-monitoring/charging functions needed to maximize battery life while powering all the new features. • An emerging TV-related feature is the ability to play back recorded still photos and short video clips from the phone to a TV set. This requires creating an analog video signal from the digitally-stored photo or video clip. • Games---improved graphics capability, user interfaces, and even sound effects.
Other reasons--- • Also, as the clock speed of digital circuitry approaches 1 GHz, analog effects in these digital circuits are playing an important role in the circuit behavior.
Which Analog circuits? • If not for the multitude of analog and mixed-signal components that vendors have developed in the past decades, the digital media river would slow to a trickle. It takes countless A/D and D/A converters—audio, video, RF—to make it possible. • It also takes basic small-signal amplifiers, audio through RF power amplifiers, • disk-drive read/write circuitry, • motor controls, line drivers and receivers, • power-supply components, • touch-screen interfaces, display drivers, • thermal sensors and fan controls, • and much more, to make the digital world possible.
Background • Basic knowledge about single stage amplifiers • Ac. Dc. Analysis techniques • Frequency response • Negative feedback
Unique Features of Analog IC Design • Geometry is an important part of the design Electrical Design →Physical Design →Test Design • Usually implemented in a mixed analog-digital circuit • Analog is 20% and digital 80% of the chip area • Analog requires 80% of the design time • Analog is designed at the circuit level • Passes for success: 2-3 for analog, 1 for digital
Analog IC Design - Continued • Electrical Aspects-Topology, W/L values, and dc currents
Analog IC Design - Continued • Physical Aspects-(Layout) -Implementation of the physical design including: - Transistors and passive components - Connections between the above - Busses for power and clock distribution • External connections • Testing Aspects -Design and implementation for the experimental verification of the circuit after fabrication
Skills Required for Analog IC Design • In general, analog circuits are more complex than digital • Requires an ability to grasp multiple concepts simultaneously • Must be able to make appropriate simplifications and assumptions • Requires a good grasp of both modeling and technology • Have a wide range of skills - breadth (analog only is rare) • Be able to learn from failure • Be able to use simulation correctly • Simulation “truths”:---(Usage of a simulator) x (Common sense) = Constant • Simulators are only as good as the models and the knowledge of those models by the designer • Simulators are only good if you already know the answers
Trends in CMOS Technology • Moore’s law: The minimum feature size tends to decrease by a factor of 1/ 2 every three years. • Semiconductor Industry Association roadmap for CMOS
Trends in IC Technology • Technology Speed: Figure of Merit vs. Time:
IC Design Development Time • A steeper ramp for the IC design development is required for every new generation of technology.
Results: • Scramble to develop new tools • Complexity is increasing with each new scaling generation • Need more trained and skilled circuit designers
Technology impact on IC Design The good: • Smaller geometries • Smaller parasitics • Higher transconductance • Higher bandwidths The bad: • Reduced voltages • Smaller channel resistances (lower gain) • More nonlinearity • Deviation from square-law behavior The ugly: • Increased substrate noise in mixed signal applications • Increased 1/f noise below 0.25µm CMOS • Threshold voltages are not scaling with power supply • Suitable models for analog design not available
ANALOG SIGNAL PROCESSING • Signal Bandwidths versus Application
Consequently: • Analog finds applications where speed, area, or power have advantages over a digital approach.
Analog Signal Processing versus Digital Signal Processing in VLSI • Key issues: • Analog/Digital mix is application dependent • Not scaling driven • Driven by system requirements for programmability/adaptability/testability/designability
Application Areas of Analog IC Design • There are two major areas of analog IC design: • Restituitive- performance oriented (speed, accuracy, power, area) Classical analog circuit and systems design • Cognitive - function oriented (adaptable, massively parallel) A newly growing area inspired by biological systems
What is the Future of Analog IC Design? • Technology will require more creative circuit solutions in order to achieve desired performance • Analog circuits will continue to be a part of large VLSI digital systems • Interference and noise will become even more serious as the chip complexity increases • Packaging will be an important issue and offers some interesting solutions • Analog circuits will always be at the cutting edge of performance
Analog designer must also be both a circuit and systems designer and must know: -Technology and modeling -Analog circuit design -VLSI digital design -System application concepts • There will be no significantly new and different technologies - innovation will combine new applications with existing or improved technologies