Download Slide 1

DIGITAL SIGNAL
Binary number
0 0000 0000
8 0000 1000
1 0000 0001
9 0000 1001
2 0000 0010
. .
3 0000 0011
. .
4 0000 0100
. .
5 0000 0101
253 1111 1101
6 0000 0110
254 1111 1110
7 0000 0111
255 1111 1111
Binary number
For decimal number
234.35= 2*102+ 2*101+4*100+3*10-1+5*10-2
For binary number
1101.01=1*23+1*22+0*21+1*20+0*2-1+1*2-2
That is
1101.01B=13.25D
Numeration System
Linguistic Hash Mark
Roman
Zero
One
Two
Three
Four
Five
Six
Seven
Eight
Nine
Ten
Eleven
n/a
I
II
III
IV
V
VI
VII
VIII
IX
X
XI
n/a
|
||
|||
||||
/|||/
/|||/ |
/|||/ ||
/|||/ |||
/|||/ ||||
/|||/ /|||/
/|||/ /|||/ |
Decimal
0
1
2
3
4
5
6
7
8
9
10
11
Binary
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
Digital-to-analog conversion
Vout
 x0 20  x1 21  x2 22 
k
n
2

 xn 1 2
n 1



reference voltage in “multiplying” DAC
i.e., 00...0 => 0 volts; 11....1 => k volts (slightly less)
k / 2n = “step size”
Digital-to-analog conversion
• When data is in binary form, the 0's and 1's may be of
several forms such as the TTL form where the logic zero
may be a value up to 0.8 volts and the 1 may be a
voltage from 2 to 5 volts.
• The data can be converted to clean digital form using
gates which are designed to be on or off depending on
the value of the incoming signal. Data in clean binary
digital form can be converted to an analog form by using
a summing amplifier.
• For example, a simple 4 bit Dac can be made with a
four-input summing amplifier. More practical is the R-2R
Network DAC.
Digital-to-analog conversion
One way to achieve D/A conversion is to use a summing amplifier
ANALOG TO DIGITAL CONVERSION
in
ANALOG
IN
ADC
DIGITAL
OUT
0v
1/51 v
2/51 v
.
.
.
253/51 v
254/51 v
5v
out
0000 0000
0000 0001
0000 0010
.
.
.
1111 1101
1111 1110
1111 1111
Digital-to-analog conversion
Illustration of 4-bit SAC with 1 volt step size
FLASH ADC
For n bits ADC we
need 2n op amps
ANALOG TO DDIGITAL
CONVERTER