AD9835 datasheet(13/28 Pages) AD

13 / 28 page

Data Sheet

AD9835

Rev. A | Page 13 of 28

THEORY OF OPERATION

Sine waves are typically thought of in terms of their magnitude

form a(t) = sin (ωt). However, these 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 = 2 πf.

MAGNITUDE

PHASE

–1

Figure 21. 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 by

ΔPhase = ωδt

Solving for ω,

ω = ΔPhase/δt = 2 πf

Solving for f and substituting the reference clock frequency for

the reference period (1/fMCLK = δt),

f = ΔPhase × fMCLK/2 π

The AD9835 builds the output based on this simple equation. A

simple DDS chip can implement this equation with three major

subcircuits.

AD9835 Datasheet(PDF) 13 Page - Analog Devices