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AD5930

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THEORY OF OPERATION

The AD5930 is a general-purpose synthesized waveform

generator capable of providing digitally programmable

waveform sequences in both the frequency and time domain.

The device contains embedded digital processing to provide a

repetitive sweep of a user programmable frequency profile

allowing enhanced frequency control. Because the device is pre-

programmable, it eliminates continuous write cycles from a

DSP/μcontroller in generating a particular waveform.

THE FREQUENCY PROFILE

The frequency profile is defined by the start frequency (FSTART),

the frequency increment (Δf) and the number of increments

per sweep (NINCR). The increment interval between frequency

increments, tINT, is either user programmable with the interval

automatically determined by the device (auto-increment mode),

or externally controlled via a hardware pin (external increment

mode). For automatic update, the interval profile can either be

for a fixed number of clock periods or for a fixed number of

output waveform cycles.

In the auto-increment mode, a single pulse at the CTRL pin starts

and executes the frequency sweep. In the external increment

mode, the CTRL pin also starts the sweep, but the frequency

increment interval is determined by the time interval between

sequential 0/1 transitions on the CTRL pin. Furthermore, the

CTRL pin can be used to directly control the burst profile, where

during the input high time, the output waveform is present, and

during the input low time, the output is reset to midscale.

The frequency profile can be swept in two different modes: saw

sweep or triangular (up/down) sweep.

Saw-Sweep Mode

In the case of a saw sweep, the AD5930 repeatedly

sweeps between sweep start to sweep end, that is, from

FSTART incrementally to

FSTART + NINCR × Δf

and then returns directly to FSTART to begin again (see Figure 31).

This gives a saw-sweep cycle time of

(NINCR + 1) × tINT

FSTART

FSTART + ∆FFSTART + NINCR × ∆F

MIDSCALE

Figure 31. Saw-Sweep Profile

Triangular-Sweep Mode

In the case of a triangular sweep, the AD5930 repeatedly

sweeps between sweep start to sweep end, that is, from FSTART

incrementally to

FSTART + NINCR × Δf

and then returns to FSTART in a decremented manner (see Figure 32).

The triangular-sweep cycle time is given by

(1 + (2 × NINCR)) × tINT

FSTART

FSTART + ∆FFSTART + ∆F

FSTART + NINCR × ∆F

MIDSCALE

Figure 32. Triangular-Sweep Profile

OUTPUT MODES

The AD5930 offers two possible output modes: continuous

output mode and burst output mode. Both of these modes are

illustrated in Figure 33.

CONTINUOUS

MODE

BURST

MODE

NUMBER STEP CHANGES

tINT

TBURST

Figure 33. Continuous Mode and Burst Mode of the AD5930

Continuous Output Mode

In this mode, each frequency of the sweep is available for the

length of time programmed into the time interval (tINT) register.

This means the frequency swept output signal is continuously

available, and is therefore phase continuous at all frequency

increments.

To set up the AD5930 in continuous mode, the CW/BURST bit

(D7) in the control register must be set to 0. See the Activating

and Controlling the Sweep section for more details.

Burst Output Mode

In this mode, the AD5930 provides a programmable burst

of the waveform output for a fixed length of time (TBURST)

within the programmed increment interval (tINT). Then for

the remainder of the tINT interval, the output is reset to mid-

scale and remains there until the next frequency increment.

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