GW Instek SFG-1000 Series - Manual (Page 9)

Getting Started
9
Technical background
Traditional
function
generators SFG-1000 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.