Datasheet

ADF4159 Data Sheet
Rev. D | Page 26 of 36
Note that the cycle slip reduction feature can only be operated
when the phase detector polarity setting is positive (Bit DB6 in
Register R3 is set to 1). It cannot be used if the phase detector
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 TX
DATA
pin.
The deviation from the center frequency is set by
f
DEV
= (f
PFD
/2
25
) × (DEV × 2
DEV_OFFSET
) (7)
where:
f
PFD
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 f
DEV
by incrementing or decrementing
the configured N divider value by DEV × 2
DEV_OFFSET
.
FSK Settings Worked Example
In this example, an FSK system operates at 5.8 GHz with a
25 MHz f
PFD
, requiring 250 kHz deviation (f
DEV
).
Rearrange Equation 7 as follows:
(DEV × 2
DEV_OFFSET
) = f
DEV
/(f
PFD
/2
25
)
(DEV × 2
DEV_OFFSET
) = 250 kHz/(25 MHz/2
25
)
(DEV × 2
DEV_OFFSET
) = 335,544.32
If DEV_OFFSET is set to 6,
DEV = 335,544.32/(2
6
) = 5242.88 ≈ 5243
Due to the rounding of DEV, f
DEV
= 250.005722 kHz.
Toggling the TX
DATA
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°)/2
12
The phase value is set in Register 1, Bits DB[14:3]. The PSK
modulation is controlled by the TX
DATA
pin.
For example, if the phase value is 1024, a logic high on the TX
DATA
pin results in a 90° increase of the output phase. A logic low on
the TX
DATA
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.
FREQUENCY
TIME
10849-028
Figure 33. Single Ramp Burst
FREQUENC
Y
TIME
10849-029
Figure 34. Single Triangular Burst
TIME
FREQUENCY
10849-030
Figure 35. Single Sawtooth Burst
FREQUENCY
TIME
10849-031
Figure 36. Continuous Sawtooth Ramp
FREQUENCY
TIME
10849-032
Figure 37. Continuous Triangular Ramp