Advertisement
't/L
$\/
DAC2
DAC2 consists of inverters and resistive ladder network and reforms the digitized data lrom DSP in sound
waveform.
The followings explain the digitalto analog conversion method
EXK-F1922064 +5
In the left figure, if the current I from the
battery is 1.5 [Al, it =0.8 IAl, i2 =0.4 [A], R
=0.2 [Al, and i4=0.1 [Al as they passthrough
lK, 2K, 4K, and 8K ohm resistors respec-
tively.
When all the switches are OFF, the output
cunent /o is 0 [A] but, if switches 51 and 53
are ON, the output current will be;
l o = i I + i g = 1 [ A l
lf all the switches are ON;
lo=il +i2 +i3 +i4= 0.1+0.2+0.4+0.8
= 1.5 [Al
Thus, digital action of switch ON/OFF is
converted into analog amount of the current.
Actually, the DAC in DH-500 is made up by
inverters and R-2R ladder network.
Instead of switches, being High or Low of
DSP's digital sound signal determines cur-
rent flow. For instance, when signal RV15 is
Low, the inverleroutput becomes High caus-
ing the current il tobeflowed. lf RV15 is High,
the current does not flow.
Since the DSP output current is too smallto
drive the DAC, lhe inverters amplify the
current.
R-2R networked resistors halve the cunent
in each ju rrction. For example, suppose current
'7 is 10 [mAl, i2 is 5 [mAI, i3 is 2.5 [mAJ.
Therefore, each bit of DSP oulput has
significance.
Namely since lhe circuit is 1 2 bit DAC, cunent
f fow from terminal RV15 is 2048 times
larger than the current from RV4.
The output cunent /o from ladder network
is transformed in voltage level by the op
amp lC8.
l - - - - - l
| * i r
I
R
Fl =25Ktl
Fl zR=soKe
8Ko
ga 6-oN
DSP
M 8 66 113 1
RV15
t/
|
2R
RV14
r/
I 2R
RV12
L/
x
l z R
RVl1
t/
l 2 R
l-l
I
n l
I
n l
I
R l
I
R .
.i
I
nl
*l
J
: . . j
l':i
- 2 2 -
Advertisement
