Appeal 2007-0018
Application 10/107,262
The first question is: What is a "frequency control word"? Hu is
directed to a direct digital synthesizer (DSS). In a DSS, enough data points
for a mathematical function (e.g., sine or cosine) are stored in digital
memory and these are recalled at the right speed and fed to a digital-to-
analog converter where the required wave function is built up. A DSS
consists of a phase accumulator that acts as an address generator for a
look-up table (LUT) which contains a digital representation of a cycle of a
desired waveform, such as the sine/cosine function. The phase is
incremented for each cycle of a reference clock. The larger the increment,
the greater the frequency as it requires fewer clock cycles to cycle through
the LUT, i.e., through one cycle of the desired waveform. The output of the
LUT is passed through a digital-to-analog converter (DAC) (discussed at
col. 8, ll. 40-42) and then to a low pass filter (mentioned at col. 8, ll. 52-55).
See, e.g., U.S. Patent 5,045,817 (discussed in Hu at col. 2, ll. 5-14) at
column 2, lines 57-68. One of ordinary skill in the art would recognize that
the "frequency control word" in Hu is a "phase increment value" which is
added to the previous accumulated phase in latch 9 to produce the next phase
angle; i.e., the content of the phase accumulator represents a phase angle
between 0 and 2π radians which is computed by adding a phase increment
value (frequency control word) to the previous phase value. The examiner's
statement that the frequency control word determines the frequency of the
programmable sine/cosine wave is correct, as would be understood by one
skilled in the DSS art.
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