Chapter 5
Signal Generation Fundamentals
©
National Instruments Corporation
5-5
NI PXIe-5450 User Manual
The following figure shows a 1 MHz sine wave generated by a 6 MS/s
DAC. The dotted line represents an aliased image signal that shows up as a
5 MHz component. In this case,
f
o
is 1 MHz,
n
is –1, and
f
s
is 6 MHz;
resulting in the following formula:
f
ai
= 5 MHz = |1 MHz + (–1)(6 MHz)|
The other possible frequencies of sine waves can be calculated and
superimposed onto the sampling points of the image.
The following figure shows the frequency domain representation of the
previous example. The vertical arrow at f
o
represents the frequency and
signal power of the desired generated signal. The other vertical arrows
represent the frequencies and signal powers of the aliased image frequency
components that appear in the frequency spectrum.
In systems where you want to generate accurate signals using sampled data,
an optional lowpass filter must be introduced after the DAC to restrict the
t
5 MHz
0
6 MHz
7 MHz
11 MHz
12 MHz
1
3
MHz
1 MHz
f
0
Signal
Power
fs
2fs
Images
