ADF4159 datasheet(30/36 Pages) AD

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ADF4159

Data Sheet

Rev. B | Page 30 of 36

Example

This example describes how to set up and use the parabolic ramp

mode with the following parameters:

•

fOUT = 5790 MHz

•

fDEV = 100 kHz

•

Number of steps = 50

•

Duration of a single step = 10 µs

To set up the parabolic ramp mode, follow these steps:

1. Configure one of the following ramp modes:

•

Continuous triangular ramp (set Register R3,

Bits DB[11:10] to 01).

•

Single ramp burst (set Register R3, Bits DB[11:10]

to 11).

For the continuous triangular ramp, the generated frequency

range is calculated as follows:

Δf = fDEV × (Number of Steps + 2) × (Number of Steps + 1)/2

= 132.6 MHz

For the single ramp burst, the generated frequency range is

calculated as follows:

Δf = fDEV × (Number of Steps + 1) × Number of Steps/2

= 127.5 MHz

2. Set the timer as described for the linear ramps in the

Timeout Interval section.

3. Activate the parabolic ramp by setting Bit DB28 in

4. Set the counter reset (Bit DB3 in Register R3) to 1 and then

set it to 0.

To activate the ramp, see the Activating the Ramp section.

Fast Ramp Mode

The ADF4159 is capable of generating a fast ramp. The fast ramp

is a triangular ramp with two different slopes (see Figure 47).

The number of steps, time per step, and deviation per step are

programmable for both the up and down ramps.

TIME

Figure 47. Fast Ramp Mode

To activate the fast ramp waveform, follow these steps:

1. Select the continuous triangular waveform by setting

Bits DB[11:10] in Register R3 to 01.

2. Enable the fast ramp by setting Bit DB19 in Register R7 to 1.

3. Program the up ramp as follows.

a. Set Bit DB6 in Register R4 (CLK DIV SEL), Bit DB23

in Register R5 (DEV SEL), and Bit DB23 in Register R6

(STEP SEL) to 0 for Ramp 1.

b. Calculate and program the timer, DEV, DEV_OFFSET,

and the step word as described in the FMCW Radar

Ramp Settings Worked Example section.

4. Program the down ramp as follows.

a. Set Bit DB6 in Register R4 (CLK DIV SEL), Bit DB23

in Register R5 (DEV SEL), and Bit DB23 in Register R6

(STEP SEL) to 1 for Ramp 2.

b. Calculate and program the timer, DEV, DEV_OFFSET,

and the step word as described in the FMCW Radar

Ramp Settings Worked Example section.

5. Start the ramp by setting Bit DB31 = 1 in Register R0.

Note that the total frequency change of the up and down ramps

must be equal for stability.

RAMP COMPLETE SIGNAL TO MUXOUT

Figure 48 shows the ramp complete signal on MUXOUT.

TIME

Figure 48. Ramp Complete Signal on MUXOUT

To activate this function, set Bits DB[30:27] in Register R0

to 1111, and set Bits DB[25:21] in Register R4 to 00011.

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