adf7012 Analog Devices, Inc., adf7012 Datasheet - Page 15

• Manufacturer Part Number: adf7012
• Description: Multichannel Ism Band Fsk/gfsk/ook/gook/ask Transmitter
• Manufacturer: Analog Devices, Inc.

The nonlinear characteristic of the output stage results in an
output spectrum containing harmonics of the fundamental,
especially the third and fifth. To meet local regulations, a low-
pass filter usually is required to filter these harmonics.
The output stage can be powered down by setting Bit PD2 in
the function register low.
GOOK MODULATION
Gaussian on-off keying (GOOK) represents a prefiltered form
of OOK modulation. The usually sharp symbol transitions are
replaced with smooth Gaussian-filtered transitions with the
result being a reduction in frequency pulling of the VCO.
Frequency pulling of the VCO in OOK mode can lead to a
wider than desired bandwidth, especially if it is not possible to
increase the loop filter bandwidth to > 300kHz.
The GOOK sampling clock samples data at the data rate:
Bits D1 to D6 represent the output power for the system for a
positive data bit. Divider Factor = 0x3F represents the max-
imum possible deviation from PA at minimum to PA at
maximum output. An index counter setting of 128 is
recommended.
Figure 32 shows the step response of the Gaussian FIR filter.
An index counter of 16 is demonstrated for simplicity. While
the pre-filter data would switch the PA directly from off to on
with a low-to-high data transition, the filtered data gradually
increases the PA output in discrete steps. This has the effect of
making the output spectrum more compact.
PA SETTING
16 (MAX)
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1 (PA OFF)
DataRate
Figure 32. Varying PA Output for GOOK (Index Counter = 16).
(0 TO 1 TRANSITION)
PRE-FILTER DATA
(
bps
)
=
DividerFac
tor
F
PFD
×
IndexCount
FILTER OUTPUT
DISCRETIZED
er
(9)
Rev. 0 | Page 15 of 28
As is the case with GFSK, GOOK requires the bit stream
applied at TxDATA to be synchronized with the sampling clock,
TxCLK (see the GFSK Modulation section).
–10
–20
–30
–40
–50
–60
–70
–80
–10
–20
–30
–40
–50
–60
–70
–80
–90
10
20
10
909.43
885.43
0
0
Figure 33. GOOK vs. OOK Frequency Spectra
Figure 34. GOOK vs. OOK Frequency Spectra
(Narrow-Band Measurement)
OOK
(Wideband Measurement)
GOOK
FREQUENCY (MHz)
FREQUENCY (MHz)
OOK
910.43
910.43
GOOK
ADF7012
935.93
910.93