ADF7020-1_15 Datasheet, PDF (19/48 Pages) Analog Devices – High Performance FSK/ASK Transceiver IC

Gaussian Frequency Shift Keying (GFSK)
Gaussian frequency shift keying reduces the bandwidth
occupied by the transmitted spectrum by digitally prefiltering
the TxData. A TxCLK output line is provided from the
ADF7020-1 for synchronization of TxData from the micro-
controller. The TxCLK line can be connected to the clock input
of a shift register that clocks data to the transmitter at the exact
data rate.
Setting Up the ADF7020-1 for GFSK
To set up the frequency deviation, set the PFD and the
modulator control bits according to the following equation:
GFSK
DEVIATION
[Hz]
=
PFD ×
2¹²
2^m
where m is GFSK_MOD_CONTROL set using R2_DB (24:26).
To set up the GFSK data rate, set the PFD and the modulator
control bits according to the following equation:
DR[bps] =
PFD
DIVIDER _ FACTOR × INDEX _ COUNTER
where DIVIDER_FACTOR and INDEX_COUNTER are
programmed in Bits R2_DB (15:21) and R2_DB (27:28),
respectively. For further information, see the Using GFSK on
the ADF7010 section in the EVAL-ADF7010EB1 data sheet.
ADF7020-1
Amplitude Shift Keying (ASK)
Amplitude shift keying is implemented by switching the output
stage between two discrete power levels. This is accomplished by
toggling the DAC, which controls the output level between two
6-bit values set up in Register 2. A 0 TxData bit sends Bits R2_DB
(15:20) to the DAC. A high TxData bit sends Bits R2_DB (9:14)
to the DAC. A maximum modulation depth of 30 dB is possible.
On-Off Keying (OOK)
On-off keying is implemented by switching the output stage to a
certain power level for a high TxData bit and switching the
output stage off for a low TxData bit. For OOK, the transmitted
power for a high input is programmed using Bits R2_DB (9:14).
Gaussian On-Off Keying (GOOK)
Gaussian on-off keying represents a prefiltered form of OOK
modulation. The usually sharp symbol transitions are replaced
with smooth Gaussian filtered transitions, 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 BW,
especially if it is not possible to increase the loop-filter BW >
300 kHz. The GOOK sampling clock samples data at the data
rate. (See the Setting Up the ADF7020-1 for GFSK section.)
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