AD9834 datasheet(15/32 Pages) AD

15 / 32 page

Data Sheet

AD9834

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 = 2πf.

MAGNITUDE

PHASE

–1

2π

4π

6π

2π

4π

6π

Figure 27. 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.

∆Phase = ω∆t

Solving for ω,

ω = ∆Phase/∆t = 2πf

Solving for f and substituting the reference clock frequency for

the reference period (1/fMCLK = ∆t),

f = ∆Phase × fMCLK/2π

The AD9834 builds the output based on this simple equation. A

simple DDS chip can implement this equation with three major

subcircuits: numerically controlled oscillator + phase modulator,

SIN ROM, and digital-to-analog converter (DAC). Each of these

subcircuits is discussed in the Circuit Description section.

Rev. D | Page 15 of 32

AD9834 Datasheet(PDF) 15 Page - Analog Devices