AD9838 View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD9838

Mixed-Signal Front-End (MxFE) Processor for Broadband Communications

Analog Devices 

AD9838

THEORY OF OPERATION

Sine waves are typically thought of in terms of their magnitude

form: a(t) = sin(ωt). However, 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

+1

6π

0

2π

4π

–1

2π PHASE

4π

6π

228

0

Figure 20. 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 as follows:

ΔPhase = ωΔt

(1)

Solving for ω,

ω = ΔPhase/Δt = 2πf

(2)

Solving for f and substituting the reference clock frequency for

the reference period (1/fMCLK = Δt),

f = ΔPhase × fMCLK∕2π

(3)

The AD9838 builds the output based on this simple equation. A

simple DDS chip can implement this equation with three major

subcircuits: numerically controlled oscillator (NCO) plus phase

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

Each subcircuit is described in the Circuit Description section.

Rev. A | Page 14 of 32

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