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SIGNAL PROCESSING WITH
ANALOG CIRCUIT
Chun Lo
Analog circuit design

Main disadvantage: low precision
 Due
to mismatch in analog circuit components such as
transistors, resistors and capacitors
 e.g. Amplifiers: lower input signal dynamic range
Comparator: lower signal resolution
Transistors: lower accuracy in current mode DAC

Advantage:
 Less
power consumption
 Possibly smaller area
Mismatch correction

By trimming device
 Larger
device, layout technique in component mismatch
 Autozeroing, correlated double sampling in amplifiers
 Cost of extra area, power and design complexity

By in herent programming elements
 Floating
gate MOSFETs

First paper
 Floating
Gates Transistors For Precision Analog circuit
Design: An Overview
 Srinivasan, Graham and Hasler

Second paper
 Analog
Floating –Gate On chip Auditory Sensing
System Interfaces
 Hasler, Smith, Graham, Ellis and Anderson
First paper

Structure of Floating Gate MOSFET
 Programming
floating gate transistors
 Programming precision
 Charge retention

Application examples of Floating Gate MOSFET
 Differential
 DAC
 ADC
pairs
MOSFET


MOS Transistor
Floating Gate MOSFET
 The
gate is completely surrounded by SiO2
 No DC to ground
 Used in Flash memory, ROM
Programming FG-MOSFET



Setting the DC voltage
Add or remove charge
Mainly two methods
 Fowler
 As
 Hot
Nordheim tunneling
a global eraser for all floating gates
electron injection
 Program
each floating gate to the desired value
individually
Programming precision

What is the smallest drain current change
I  I o exp(
Vg
UT
I  I  I o exp(
) exp(
Vs
)
UT
 (Vg  Vg )
UT
Vg
I
 exp(
) 1
I
UT
) exp(
Vs
)
UT
V 
Q
CT
I
Q
 exp(
) 1
I
U T CT

A single electron change results in an accuracy of
2.8 X 104 or 12 bits
Charge Retention

Short term drift
 Observed
immediately after programming
 Proportional to the amount of change that is
programmed into the floating gate

Long term charge loss
 Themionic
emission
 Related to both temperature and time
Applications



Differential pair
DAC
ADC
Second paper

Advance in analog VLSI circuits
 Performance
close to DSP
 More option for designeer




Analog Digital Partition
Signal Processing Circuits
Noise Suppression for speech enhancement
Speech Recognition
Analog Digital Partitioning

Power and space
 No
overhead for tuning and programming
 Work in subthreshold save power

SN VS Cost
Analog Signal Processing
Noise suppression

Main Idea: Attenuate the noise components
Speech Recognition

HMMs
 States,
transition probabilities and
 Hidden states are words, output is audio signal
produced by speaker
 Recognition problem: what is the state of the system