ADF7020BCP datasheet(15/40 Pages) AD

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Preliminary Technical Data

ADF7020

Rev. PrH | Page 15 of 40

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 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 for GFSK

To set up the frequency deviation, set the PFD and the mod

control bits:

]

[

DEVIATION

PFD

GFSK

where m is GFSK_MOD_CONTROL set using R2_DB(24:26).

To set up the GFSK data rate:

COUNTER

INDEX

FACTOR

DIVIDER

PFD

]

bps

[

For further information, see the application note, Using GFSK

on the ADF7010, in the EVAL-ADF7010EB1 Technical Note.

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 zero 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 zero. For OOK, the transmitted power for

a high input is programmed using Bits R2_DB(9:14).

Gaussian On-Off Keying (G-OOK)

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 G-OOK sampling clock samples data at the data

rate. (See the Setting Up the ADF7020 for GFSK section.)

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