TRF2443IPFPR datasheet(63/72 Pages) TI

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Baseband-Filter Cutoff-Frequency Calibration

LPF BW Adj (dec)

90 100 110 120

G070

RXBB I

RXBB Q

LPF BW Adj (dec)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

90 100 110 120

G071

RXBB I

RXBB Q

TRF2443

www.ti.com ................................................................................................................................... SLWS217A – SEPTEMBER 2009 – REVISED SEPTEMBER 2009

The TRF2443 internal feedback path can be used to set up an automatic calibration of the RX baseband-filter

cutoff frequency. The procedure to calibrate the corner frequency to 3 MHz is described as follows.

1. Enable loopback switch with minimum insertion loss.

EN_LB_ATT = 0 (SPI-3, register 1, B<19>)

EN_LB = 1 (SPI-3, register 1, B<18>)

2. Program RXLO to 165 MHz (RXLO to 2640 MHz and RX divider to 16).

RXRDIV<13,0> = <00 0000 0000 0001> (SPI-2, register 1, B<18,5>) [R = 1]

RX_NINT<15,0> = <0000 0000 1000 0100> (SPI-2, register 2, B<20,5>) [N = 132]

RXDIV_SEL = 0 (SPI-2, register 2, B<26>) [LO divider set to 16]

3. Set TXVCO divider to 16.

TXDIV_SEL = 0 (SPI-1, register 2, B<26>) [LO divider set to 16]

4. Set the TXPLL PFD frequency to 4 MHz (R divider = 5).

TXRDIV<13,0> = <00 0000 0000 0101> (SPI-1, register 1, B<18,5>) [R = 5]

5. Apply a dc offset at the TRF2443 TX baseband inputs (to increase the TXLO leakage at the modulator

output).

6. Set the RX baseband amplifier gain to 22 dB.

RXBB_GAIN<4,0> = <01101> (SPI-3, register 2, B<15,11>)

7. Set the RX baseband cutoff-frequency bit controls RXBB_FREQ<6,0> = 011 1000 (typical value for fC = 3

MHz)

8. Program the TXLO frequency to 166 MHz (TXVCO = 2656 MHz).

TX_NINT<15,0> = <0000 0001 0100 1100> (SPI-1, register 2, B<20,5>) [N = 332]

9. Measure the RX baseband output-power level (at I or Q output): Pout1.

10. Program the TXLO frequency to 168 MHz (TXVCO = 2688 MHz).

TX_NINT<15,0> = <0000 0001 0101 0000> (SPI-1, register 2, B<20,5>) [N = 336]

11. Measure the RX baseband output power level (Pout2) and calculate attenuation: Att = Pout1 – Pout2.

12. If Att < 3 dB, then increase RXBB_FREQ and go back to 11); else if Att > 3 dB, then reduce RXBB_FREQ

and go back to 11). This is repeated until two sequential iterations result in the calculated attenuation being

above and below 3 dB. When this is observed, save the RXBB_FREQ value which results in an attenuation

value closer to 3 dB.

The TRF2443 baseband low-pass filter cutoff frequency can be programmed to any of 128 cutoff frequencies.

The cutoff frequency control consists of 7 bits, RXBB_FREQ<6,0>, which are located in SPI-3, register 2,

B<22,16>. RXBB_FREQ<6,0> = <111 1111> corresponds to the minimum corner frequency. Figure 108 shows

the 3-dB bandwidth of the filter versus all possible SPI codes for a typical unit. Figure 109 shows the inverse of

the 3-dB bandwidth versus all possible SPI codes for a typical unit.

Figure 108. BW vs SPI Code (RXBB_FREQ<6,0>

Figure 109. 1/BW vs SPI Code (RXBB_FREQ<6,0>

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