ADF4159 datasheet(25/36 Pages) AD

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Data Sheet

ADF4159

Rev. B | Page 25 of 36

Note that the cycle slip reduction feature can only be operated

when the phase detector polarity setting is positive (Bit DB6 in

polarity is negative.

MODULATION

The ADF4159 can operate in frequency shift keying (FSK) or

phase shift keying (PSK) mode.

Frequency Shift Keying (FSK)

FSK is implemented by configuring the ADF4159 N divider

for the center frequency and then toggling the TXDATA pin.

The deviation from the center frequency is set by

fDEV = (fPFD/225) × (DEV × 2DEV_OFFSET)

(7)

where:

fPFD is the PFD frequency.

DEV is a 16-bit word (Bits DB[18:3] in Register R5).

DEV_OFFSET is a 4-bit word (Bits DB[22:19] in Register R5).

The ADF4159 implements fDEV by incrementing or decrementing

the configured N divider value by DEV × 2DEV_OFFSET.

FSK Settings Worked Example

In this example, an FSK system operates at 5.8 GHz with a

25 MHz fPFD, requiring 250 kHz deviation (fDEV).

Rearrange Equation 7 as follows:

(DEV × 2DEV_OFFSET) = fDEV/(fPFD/225)

(DEV × 2DEV_OFFSET) = 250 kHz/(25 MHz/225)

(DEV × 2DEV_OFFSET) = 335,544.32

If DEV_OFFSET is set to 6,

DEV = 335,544.32/(26) = 5242.88 ≈ 5243

Due to the rounding of DEV, fDEV = 250.005722 kHz.

Toggling the TXDATA pin causes the frequency to hop between

±250 kHz from the programmed center frequency.

Phase Shift Keying (PSK)

When the ADF4159 is configured for PSK mode, the output

phase of the ADF4159 is equal to

(Phase Value × 360°)/212

The phase value is set in Register 1, Bits DB[14:3]. The PSK

modulation is controlled by the TXDATA pin.

For example, if the phase value is 1024, a logic high on the TXDATA

pin results in a 90° increase of the output phase. A logic low on

the TXDATA pin results in a 90° decrease of the output phase. The

polarity can be inverted by negating the phase value.

WAVEFORM GENERATION

The ADF4159 is capable of generating five types of waveforms

in the frequency domain: single ramp burst, single triangular

burst, single sawtooth burst, continuous sawtooth ramp, and

continuous triangular ramp. Figure 33 through Figure 37 show

the types of waveforms available.

TIME

Figure 33. Single Ramp Burst

TIME

Figure 34. Single Triangular Burst

TIME

Figure 35. Single Sawtooth Burst

TIME

Figure 36. Continuous Sawtooth Ramp

TIME

Figure 37. Continuous Triangular Ramp

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