Processing of Natural Signals

1
Processing of Natural Signals

• Natural Signals are analog and may be small
• Range microvolts to hundreds of millivolts

2
Digital Communications

• E.g. Multi-level signaling rather than binary

3
Disk Drive Electronics

• Magnetic information converted to electric signal
  with high noise needs filtered.

4
Wireless Receivers

• Antenna signals are 1GHz and microvolt levels
  plus lots of added noise.

5
Optical Receivers

• Need electrical-to-optical (E2O) and optical
  to-electrical (O2E) converters.
• Receiver must work fast at low voltage level.

6
Sensors

• Mechanical, electrical, optical sensors are
  everywhere and in noisy environments.
• E.g. airbag sensors have lt1 variation in C.

7
Microprocessors and Memory

• Modern systems use analog design expertise for
  distribution and timing of data and clocks across
  a large chip or among chips.
• Memory uses high-speed sense amplifiers
  extensively.
• Nonidealities in signal and power interconnects
  on chip and in package.
• High-speed digital design is analog design!

8
Why is Analog Design Difficult?
Design Trade-Offs

• Digital Design Trade-Offs
• Speed
• Power dissipation

• Analog Design Trade-Offs
• Speed
• Power dissipation
• Gain
• Precision
• Supply Voltage
• And more!

9
Why is Analog Design Difficult?
Other Issues

• Analog circuits are more sensitive to noise,
  crosstalk, and other interferers than digital.
• Second-order effects in devices affect analog
  devices more heavily than digital.
• Analog circuits can rarely be automated requiring
  every device to be hand-crafted.
• Modeling and simulation of many effects in analog
  circuits are limited. Requires experience and
  intuition when analyzing simulation results!

10
Why is Analog Design Difficult?
The Semiconductor Medium Itself

• Mainstream IC technology is developed and
  characterized for digital applications.
• These technologies do not easily lend themselves
  to analog design.
• Analog design requires novel circuits and
  architectures to achieve a high performance in
  this medium.

11
Why Integrated?

• Conceived in the late 1950s.
• Evolved from a few components to more than one
  billion transistors.
• Moores Law Transistor count per chip doubles
  every 1.5 years.
• Minimum dimension has dropped from 25um in 1960
  to 0.18um in 2000.
• Allows complexity, speed, and precision that
  would be impossible with discrete implementations.

12
Why CMOS for Analog?

• Low cost of fabrication
• Both analog and digital circuits can be on the
  same chip.
• Improve overall performance
• Reduce cost of packaging
• Principal reason is device scaling continues to
  improve speed of MOSFETs.

13
Levels of Abstraction
14
Robust Analog Design

• Device and circuit parameters vary with the
  fabrication process, supply voltage, and ambient
  temperature (PVT).
• Circuits must be designed for acceptable
  performance over a specified range of PVT.
• Difficult since device parameters vary
  significantly from wafer to wafer.