A Software based DDS for 137Kc By Dieter Wulff, DK5PT. A short
description of an experimental DDS This DDS-development should
not be a competitor to the readily available DDS systems and ICs
from ANALOG -DEVICES et. al. The goal was to develop a cheap,
amateur solution. After tests and experience with a DDS, made of
discrete HC-MOS circuits which filled a complete lab-pcb. The
idea was to replace the glue-logic by software. - A bit of DDS-
theory The main components of a DDS or numerical oscillator,
NCO, are: - the phase register - the phase accumulator - A clock
oscillator - lookup table The phase register holds the value of
the phase increments. Every clock cycle this value is added to
the preceding one. The result is latched and fed back to the
binary adder. The greater the value in the phase register, the
faster the DDS steps through the signal phase, the higher the
frequency. A complete phase cycle is finished, when the phase
acc. rolls over. To generate the output signal A(t), the linear
phase informatio