CC1020-RTR1 datasheet(28/95 Pages) TI1

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307.2

ChBW

(DEC _ DIV 1) kHz

CC1020

SWRS046H – NOVEMBER 2006 – REVISED MARCH 2015

www.ti.com

In Manchester mode the maximum modulating signal occurs when transmitting a continuous sequence of

0s (or 1s). In NRZ mode the maximum modulating signal occurs when transmitting a 0-1-0 sequence. In

both Manchester and NRZ mode 2 × fm is then equal to the programmed baud rate. The equation for

SBW can then be rewritten as shown in Equation 14.

SBW = Baud rate + frequency separation

(14)

Furthermore, the frequency offset of the transmitter and receiver must also be considered. Assuming

equal frequency error in the transmitter and receiver (same type of crystal) the total frequency error is

shown in Equation 15.

f_error = ±2 × XTAL_ppm × f_RF

(15)

Where:

XTAL_ppm is the total accuracy of the crystal including initial tolerance, temperature drift, loading and

ageing.

F_RF is the RF operating frequency.

The minimum receiver channel filter bandwidth (ChBW) can then be estimated as shown in Equation 16.

ChBW > SBW + 2 × f_error

(16)

The DEC_DIV[4:0] bits in the FILTER register control the receiver channel filter bandwidth. The 6 dB

bandwidth is given by Equation 17.

(17)

Where:

the IF frequency is set to 307.2 kHz.

In SmartRF Studio the user specifies the channel spacing and the channel filter bandwidth is set

according to Table 5-5.

For narrowband systems with channel spacings of 12.5 and 25 kHz the channel filter bandwidth is 12.288

kHz and 19.2 kHz respectively to comply with ARIB STD-T67 and EN 300 220.

For wideband systems (channel spacing of 50 kHz and above) it is possible to use different channel filter

bandwidths than given in Table 5-5.

There is a trade-off between selectivity as well as sensitivity and accepted frequency tolerance. In

applications where larger frequency drift is expected, the filter bandwidth can be increased, but with

reduced adjacent channel rejection (ACR) and sensitivity.

Table 5-5. Channel Filter Bandwidths Used for the Channel Spacings Defined in SmartRF Studio

FILTER.DEC_DIV

CHANNEL SPACING

FILTER BANDWIDTH

[4:0]

[kHz]

[decimal(binary)]

12.5

12.288

24 (11000b)

19.2

15 (01111b)

25.6

11 (01011b)

100

51.2

5 (00101b)

150

102.4

2 (00010b)

200

153.6

1 (00001b)

500

307.2

0 (00000b)

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