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 pairs  DAC  ADC

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 Nordheim tunneling As a global eraser for all floating gates  Hot electron injection Program each floating gate to the desired value individually

Programming precision  What is the smallest drain current change  A single electron change results in an accuracy of 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