AD9833 datasheet(11/24 Pages) AD

11 / 24 page

Data Sheet

AD9833

Rev. E | Page 11 of 24

THEORY OF OPERATION

Sine waves are typically thought of in terms of their magnitude

form: a(t) = sin(ωt). However, these sine waves are nonlinear and

not easy to generate except through piecewise construction. On

the other hand, the angular information is linear in nature. That

is, the phase angle rotates through a fixed angle for each unit of

time. The angular rate depends on the frequency of the signal

by the traditional rate of ω = 2πf.

MAGNITUDE

PHASE

–1

2π

4π

6π

2π

4π

6π

Figure 23. Sine Wave

Knowing that the phase of a sine wave is linear and given a

reference interval (clock period), the phase rotation for that

period can be determined.

ΔPhase = ωΔt

Solving for ω,

ω = ΔPhase/Δt = 2πf

Solving for f and substituting the reference clock frequency for

the reference period (1/fMCLK = Δt)

f = ΔPhase × fMCLK∕2π

The AD9833 builds the output based on this simple equation. A

simple DDS chip can implement this equation with three major

subcircuits: numerically controlled oscillator (NCO) and phase

modulator, SIN ROM, and digital-to-analog converter (DAC).

Each subcircuit is described in the Circuit Description section.

AD9833 Datasheet(PDF) 11 Page - Analog Devices