SFG-2000 Series User Manual 
10 
Technical background 
Traditional 
function 
generators 
SFG-2000 series uses the latest Direct Digital Synthesis 
(DDS) technology to generate stable, high resolution 
output frequency. The DDS technology solves several 
problems encountered in traditional function generators, 
as follows. 
Constant current circuit methodology 
This analog function generating method uses a constant 
current source circuit built with discrete components 
such as capacitors and resistors. Temperature change 
inside the generator greatly affects the components 
characteristics which lead to output frequency change. 
The results are poor accuracy and stability. 
DDS 
methodology 
In DDS, the waveform data is contained in and 
generated from a memory. A clock controls the counter 
which points to the data address. The memory output is 
converted into analog signal by a digital to analog 
converter (DAC) followed by a low pass filter. The 
resolution is expressed as fs/2k where fs is the frequency 
and k is the control word, which contains more than 
28bits. Because the frequency generation is referred to 
clock signal, this achieves much higher frequency stability 
and resolution than the traditional function generators. 
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