CC1070-RTR1 datasheet(24/57 Pages) TI2

24 / 57 page

CC1070

SWRS043A

Page 24 of 54

FSK frequency deviation is programmed in

the DEVIATION register. The deviation

programming is divided into a mantissa

(TXDEV_M[3:0])

and

exponent

(TXDEV_X[2:0]).

Generally REF_DIV should be as low as

possible but the following requirements

must be met

[]

MHz

ref

256

8304

≥

in the frequency band 402 – 470 MHz, and

[]

MHz

ref

512

8304

≥

in the frequency band 804 – 940 MHz.

The PLL output frequency equation above

gives the carrier frequency, fc , in transmit

mode (center frequency). The two FSK

modulation frequencies are given by:

f0 = fc − fdev

f1 = fc + fdev

where fdev is set by the DEVIATION

)

(

−

⋅

TXDEV

ref

dev

TXDEV

in the frequency band 402 - 470 MHz, and

)

(

−

⋅

TXDEV

ref

dev

TXDEV

in the frequency band 804 - 940 MHz.

OOK

(On-Off

Keying)

used

TXDEV_M[3:0] = 0000.

The TX_SHAPING bit in the DEVIATION

modulation signal.

11.1 Dithering

Spurious signals will occur at certain

frequencies depending on the division

ratios in the PLL. To reduce the strength of

these spurs, a common technique is to

use a dithering signal in the control of the

frequency dividers. Dithering is activated

by setting the DITHER bit in the FREQ_0

registers. It is recommended to use the

dithering in order to achieve the best

possible performance.

12 Transmitter

12.1 FSK Modulation Formats

The data modulator can modulate FSK,

which is a two level FSK (Frequency Shift

Keying), or GFSK, which is a Gaussian

filtered FSK with BT = 0.5. The purpose of

the GFSK is to make a more bandwidth

efficient system. The modulation and the

Gaussian filtering are done internally in the

chip. The

TX_SHAPING bit in the

DEVIATION register enables the GFSK.

GFSK is recommended for narrowband

operation.

12.2 OOK Modulation

The data modulator can also do OOK (On-

Off Keying) modulation. OOK is an ASK

(Amplitude Shift Keying) modulation using

100% modulation depth.

OOK modulation is enabled by setting

TXDEV_M[3:0] = 0000 in the DEVIATION

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