Class-D Amplifier Front End (POSTER) by ttz13568


									                                                   Class-D Amplifier Front End
                                                           Steven E. Turner & Wayne H. Slade Jr.

Class-D amplifiers                           are
becoming key components of low power
                                                                                                                                                                                                                                              System Components
modern consumer devices. Their high                                                                                                                                                                                                           & Features
efficiency makes them ideal audio amplifiers
                                                                                                                                                                                                                                              •Bistable Oscillator (Triangle and Square Wave)
in laptops, cell-phones, subwoofers, and
other mobile audio devices. This VLSI
                                                                                                                                                                                                                                              •Wide Swing Operational Amplifier
project implements the signal processing
                                                                                                                                                                                                                                              •Analog Comparator
"front end" component of a class-D
                                                                                                                                                                                                                                              •Digital Volume Control
amplifier. The inputs to the circuit are
                                                                                                                                                                                                                                              •Input Buffers
stereo line-in audio, and the outputs are
                                                                                                                                                                                                                                              •ESD Protection
designed to drive an H-bridge for each
                                                                                                                                                                                                                                              •Test and Characterization Circuits
audio channel. Volume control has also
been implemented as a five-bit digital                  Layout view of circuit
                                                                                                                                                                                                                                                                                                                                        Preamp                                                PWM Signal
number input.                                                                                                                                                                                                                                                                                                                                                                                 Out

                                                   Circuit Design                was performed                                                                                                                                                  Signal
     Ram p
     W ave
                                                   using Cadence circuit design and simulation
                                                   software, by Cadence Design Systems Inc.                                                                                                                                                                                                                                                                      Triangle Wave
    M essage
                                                   The design was sent to MOSIS and                                                                                                                                                                                                                                                                              Source
    S ig n a l
                                                   fabricated at an AMI foundry using the C5N        Microphotograph collage of circuit, 200x                                                                                                                                                                           Component level schematic
                                                   CMOS process. This process is a 5 volt,           magnification (actual size 1.5 x 1.5 mm)
    PW M
    S ig n a l
                                                   L=0.5micron, 3 metal process, defined by
                                                   17 masks.                                                                                                                                                             Test Results
          Theory of pulse-width modulation
                                                                                                                                                                                  Triangle Wave Output                                                                                                                                   S quare Wave Output
                       (PWM)                                                                                                                      4                                                                                                                        3


                                                                                                                                                                                                                                                  Output Waveform [volt]
                                                                                                                  Output Waveform [volt]

The Class-D amplification method offers                                                                                                                                                                                                                                    1

                                                                                                                                                  0                                                                                                                        0
simplicity in design and consequently in                                                                                                                                                                                                                                   -1

construction.    Compared to other design

classes, the Class-D design provides higher
                                                                                                                                                  -4                                                                                                                       -3
                                                                                                                                                       0      200           400            600              800          1000          1200                                     0                                     200         400             600              800     1000        1200
                                                                                                                                                                                       Time S ample                                                                                                                                           Time S ample

efficiency in a smaller enclosure. This class-                                                                                                             220kHz Triangle wave output (left) & 220kHz Square wave output (right)
D design is implemented in a 0.5 micron                                                                                                                                                                                                                                                                                                          S ys tem Output
                                                                                                                                                                                  S ys tem Input

CMOS process. The design accepts as input                                                                                                          4                                                                                                                                                         3

                                                                                                                                                   3                                                                                                                                                         2

a stereo signal from an audio source, such

                                                                                                                                                                                                                                                                                    Output Waveform [volt]
                                                                                                                                                   2                                                                                                                                                         1

                                                                                                                          Input Waveform [volt]
                                                                                                                                                   1                                                                                                                                                         0

as a CD player, and provides as output, a                                                                                                          0


“pulse-width modulated” signal to an H-

                                                        Microphotograph of 20k-ohm resistor (left)

bridge drive circuit, which is in turn used to                                                                                                    -4                                                                                                                                                         -4

                                                         Layout view of wide-swing op-amp (right)
                                                                                                                                                       0     200      400             600             800         1000          1200                                                                              0         200         400           600            800    1000      1200
                                                                                                                                                                                  Time S ample                                                                                                                                                    Time S ample

drive a loudspeaker.                                                                                                                                               20kHz sine wave input (left) & corresponding PWM output (right)

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