Digital Signal Processing Reference
In-Depth Information
The D/A converter simulated here is a module in which mathematical formulae can be
inputted. The formula inputted in this example is
IN (0)
<
16 + IN(1)
<
8 + IN (2)
<
4 + IN(3)
<
2 + IN(4)
<
1
or alternatively
IN(0)
<
2
4
+ IN(1)
<
2
3
+ IN(2)
<
2
2
+ IN(3)
<
2
1
+ IN(4)
<
2
0
Thus the bit with highest weight lies at the input IN(0) and the lowest at IN(4). Please note
that this is a pure simulation intended to demonstrate the underlying principle.
Analog pulse modulation processes
The pulse duration modulation in the case of the A/D converter shown in Illustration 187
is of great importance in microelectronic measuring and automatic control technology.
Alongside these analog pulse modulation processes - as a result of the continuously
modifiable pulse length the information is present in analog form - there are other
important analog pulse modulation processes within the framework of measuring and
automatic control technology, which are as follows
• Puse
amplitud
e modulation PAM
• Puse
duration
modulation PDM
• Puse
frequency
modulation PFM
• Puse
phase
modulation PPM
These pulse modulation processes are of practically no importance in transmission
technology. They serve usually as intermediate processes in the conversion of analog
“measurement values” into digital signals.
The PAM simply describes the sampling of an analog signal as shown in Illustration 184.
The Sample & Hold process is simply a variant of the PAM.
Characteristic of the other three analog pulse modulation processes is the conversion of
analog measurement values into analog time length. As very small and precise units of
time are available in microelectronics thanks to quartz technology the comparision of
times can be carried out extremely accurately using the instruments of microelectronics.
In Illustration 187 the different analog pulse modulation processes are shown. The A/D
conversion according to Illustration 184 was modified and added to:
• The PPM signal was obtained by triggering on the negative edge of the PDM signal.
The pulse width of the PPM signal was set in the menu of the trigger module.
• The PFM signal was obtained by a frequency modulator. To this end the offset and
amplitude of the LF signal - output 5 of the function generator module - were
changed accordingly.
