Download - DTMF Project
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2014 Synopsys, Inc. All rights reserved. 1
Digital Track: Project
DTMF signal generator
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2014 Synopsys, Inc. All rights reserved. 2
Agenda
DTMF
CORDIC
Fixed point arithmetic
Project
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DTMF
Dual Tone Multiple Frequency
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Dual-tone multi-frequency signaling
Used for telecommunication signaling over analog
telephone lines
Introduced by AT&T in 1963. Replaced the rotary dial.
Standardized by ITU
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Example of DTMF signal
DTMF output is the sum of a low and a high frequency
sinusoidal waves
697 Hz Sine Wave + 1209 Hz Sine Wave = DTMF Tone "1"
+ =
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DTMF Keypad: Frequencies
1209 Hz 1336 Hz 1477 Hz 1633 Hz
697 Hz 1 2 3 A
770 Hz 4 5 6 B
852 Hz 7 8 9 C
941 Hz * 0 # D
Upper band
Lower
band
Keypad is a 4x4 matrix
Rows represents low frequencies
Columns represents high frequencies
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Mark and space
The time which a Dtmf digit tone is actually producing
signaling, is called the "Mark" time.
The silence after a mark is called the "Space".
Most Dtmf decoders and controllers will list a minimum
Mark/Space speed, expressed in millisecond
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CORDIC
COordinate Rotation DIgital Computer
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We need to create sine waves
We only have logic gates and flip flops
Several approaches could exists to calculate the
trigonometric functions
Most of them will require multipliers and dividers which are
expensive in terms of performance and area
We need an alternative to compute these functions
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COordinate Rotation DIgital Computer:
CORDIC
Also known as the digit-by-digit method and Volder's
algorithm (1959)
It is a simple and efficient algorithm to calculate
hyperbolic and trigonometric functions.
It is commonly used when no hardware multiplier is
available (e.g., simple microcontrollers and FPGAs)
It only requires: addition, subtraction, bit-shift and table
lookup.
It can lead to an area efficient hardware implementation
For k bit precision, k iterations are required
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CORDIC bases
It uses pseudo-rotations with fixed angles.
it explodes mathematical properties of , and .
fixed angles are selected to use division by 2 (binary
shift)
more info: http://en.wikibooks.org/wiki/Digital_Circuits/CORDIC and Google
http://en.wikibooks.org/wiki/Digital_Circuits/CORDIChttp://en.wikibooks.org/wiki/Digital_Circuits/CORDIC
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Using the Cordic: rotation mode
+1 = 2
+1 = + 2
+1 =
= arctan 2 values are
precomputed
= ()
if 0 =1
and 0 = 0 then
= cos 0
= sin(0)
= 1 + 21=0
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Fixed point arithmetic
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Fixed-point number representation (1/2)
Value of a n-bit binary fixed point number with digits :
= 2 21
=0 = 21
=0
where:
is a constant giving the position of the binary point (from left)
resolution: = 2
number of fractional bits: = .
Signed numbers: use 2s complement. Notation: .
0 1 0 . 1 1 1 0 0
f p s
8 bits
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Fixed-point number representation (2/2)
Binary fixed-point to decimal: to convert to an integer and
multiply by
Decimal number to fixed-point binary number:
(a) multiply by 2
(b) round to nearest whole integer (max. error = r/2)
(c) resulting decimal integer to binary integer
0 1 0 . 1 1 1 0 0
f p s
8 bits
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example and operations
E.g.:
The four basic operations (+,-,*,/) on fixed-point binary
numbers can be performed as if they were integers.
Adding two . fixed-point numbers could give a result that is a ( + 1). fixed-point number.
Format Number r Integer Value
1.3 1.011 0.125 (2^-3) 11 1.375 (11/8)
s1.3 01.011 0.125 (2^-3) 11 1.375 (11/8)
s1.3 11.011 0.125 (2^-3) -5 -0.625 (-5/8)
2.4 10.0111 0.0625 (2^-4) 39 2.4375 (39/16)
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Project
DTMF Generator
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2014 Synopsys, Inc. All rights reserved. 18
Objective
To design and implement a simple DTMF generator
No silences between key changes are required
No digital to analog conversion
To use CORDIC algorithm to calculate sine or cosine
To use Fixed-point numbers for calculations.
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Specifications
Output of 16 bits named out[15:0]
Input of 5 bits for keypad named key[4:0]
16 key stroke combinations + 1 no-stroke
unused combinations must not produce signaling
Asynchrony Reset called rst
Pin Clock clk
Clock frequency must be determined by you.
mark=40ms; space=40ms
Minimize Power and Area, but achieve accurate timing
All paths must complete on a clock period
Accurate output wave frequencies are required.
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Stamp the idea in paper
DMFT Diagram
sin(wt)
CORDIC
keypad
Digital Input
sin(wt)
CORDIC
Modulated
Digital Tone
DECODE
Frequency
Lookup
Table
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Can we physically implement our
designs?
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MOSIS (Metal Oxide Semiconductor
Implementation Service)
Is probably the oldest (1981) integrated circuit (IC)
foundry service
MOSIS is operated by the Information Sciences Institute
at the University of Southern California (USC)
MOSIS has prototyped more than 50,000 chip designs
for private businesses, government agencies, research
agencies and universities
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MOSIS Educational Program (MEP)
Instructional Program
The MOSIS Instructional program provides free fabrication of
integrated circuits designed by students in organized classes
associated with an accredited university.
These runs are currently sponsored by MOSIS.
Available technologies:
ON Semiconductor 0.50 micron C5 (5 parts per design)
IBM 0.18 micron 7RF (14 parts per design)
Max die size: 1.5mmX1.5mm
MOSIS will provide ceramic or OCP packaging
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DIP 28 package
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Thank You