312
Chapter 7 Tutorial
Direct Digital Synthesis
7
The 33210A represents amplitude values by 16,384 discrete voltage
levels (or 14-bit vertical resolution). The specified waveform data is
divided into samples such that one waveform cycle exactly fills waveform
memory (see the illustration below for a sine wave). If you create an
arbitrary waveform that does not contain exactly 8K points, the
waveform is automatically “stretched” by repeating points or by
interpolating between existing points as needed to fill waveform memory.
Since all of waveform memory is filled with one waveform cycle, each
memory location corresponds to a phase angle of 2
π
/8,192 radians.
Sine Wave Representation in Waveform Memory
Direct digital synthesis (DDS) generators use a phase accumulation
technique to control waveform memory addressing. Instead of using a
counter to generate sequential memory addresses, an “adder” is used
(see the following page). On each clock cycle, the constant loaded into
the phase increment register (PIR) is added to the present result in the
phase accumulator. The most-significant bits of the phase accumulator
output are used to address waveform memory. By changing the PIR
constant, the number of clock cycles required to step through the entire
waveform memory changes, thus changing the output frequency.
The PIR determines how fast the phase value changes with time and
thereby controls the frequency being synthesized. More bits in the phase
accumulator result in finer frequency resolution. Since the PIR affects
only the rate of change of the phase value (and not the phase itself),
changes in waveform frequency are phase-continuous.
+8191
2047
Memory Address
4095
DAC
Code
(Phase)
-8191
(90°)
(180°)
6143
(270°)
8191
(360°)
0
33210A users guide.book Page 312 Wednesday, July 16, 2008 11:16 AM
Summary of Contents for 33210A
Page 1: ...Keysight 33210A 10 MHz Function Arbitrary Waveform Generator User s Guide ...
Page 2: ......
Page 3: ......
Page 14: ...12 Contents Contents 33210A users guide book Page 12 Wednesday July 16 2008 11 16 AM ...
Page 15: ...1 1 Quick Start 33210A users guide book Page 13 Wednesday July 16 2008 11 16 AM ...
Page 53: ...3 3 Features and Functions 33210A users guide book Page 51 Wednesday July 16 2008 11 16 AM ...
Page 273: ...5 5 Error Messages 33210A users guide book Page 271 Wednesday July 16 2008 11 16 AM ...
Page 301: ...6 6 Application Programs 33210A users guide book Page 299 Wednesday July 16 2008 11 16 AM ...
Page 311: ...7 7 Tutorial 33210A users guide book Page 309 Wednesday July 16 2008 11 16 AM ...
Page 335: ...8 8 Specifications 33210A users guide book Page 333 Wednesday July 16 2008 11 16 AM ...