TRF2443IPFPR datasheet(55/72 Pages) TI

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Baseband Section

TRANSMITTER DESCRIPTION

FromSPI

0/90

Tofeedback

switch

From TX

PLL

TX_OUT

TXQ_IN

TXI_IN

Level

Detect

TX_PWD

ATT

TXAMP

TX IQ Modulator

TRF2443

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

The TRF2443 baseband section integrates a programmable gain amplifier (PGA) and programmable low-pass

filter. The baseband PGA minimum gain is 9 dB, and the maximum gain is 33 dB. The PGA can be programmed

in 25 gain settings (0 to 24) in 1-dB increments. Its gain can be changed by the RX_BBGAIN<4,0> bits (SPI-3,

gain_setting = wanted_gain – 9.

Example: Wanted gain = 22 dB

→ New gain setting = 22 – 9 = 13 = <0 1101>

The TRF2443 baseband low-pass filter cutoff frequency can be programmed from 2 MHz to 11 MHz by setting

appropriately

the

cutoff-frequency

control

bits

RXBB_FREQ<6,0>

(SPI-3,

B<22,16>).

RXBB_FREQ<6,0> = <111 1111> corresponds to the minimum corner frequency.

The baseband output buffers (ADC drivers) are designed to drive directly an analog-to-digital converter (ADC),

either dc- or ac-coupled. The output common mode of the ADC drivers is set externally via the RXBBCM pin (pin

40). When the TRF2443 is dc-connected to the ADC, the same dc common mode for both the ADC and the

TRF2443 baseband output can be used.

Figure 102. Transmitter Chain Block Diagram

The transmitter chain integrates an IQ modulator followed by a variable attenuator and the final transmitter

amplification stage. The last two blocks provide over 35 dB of gain range. A power-alarm circuit monitors the

level at the modulator output, and its digital output goes low if the signal level falls below the user-specified

threshold level relative to the expected level.

The first block of the transmitter chain is the IQ modulator, which upconverts the incoming in-phase and

quadrature signals to the TX IF frequency. The TRF2443 can be either ac- or dc-coupled to the digital-to-analog

converter (DAC). If a dc-coupled configuration is selected, then the modulator-input dc-common mode must be

set externally to the appropriate level of 1.4 V and the common-mode bias generation must be set to external

mode via the SPI by setting EN_TXCM (SPI-3, register 3, B<31>) to 1. If an ac-coupled configuration is selected,

then internal common-mode generation mode must be enabled via the SPI by setting EN_TXCM (SPI-3, register

3, B<31>) to 0. When internal biasing is enabled, it is possible to apply a dc offset to either the I or Q side of the

IQ modulator using the integrated dc DAC, accessible via the SPI (TXBBI<5,0>, SPI-3, register 3, B<30,25>;

TXBBQ<5,0>, SPI-3, register 3, B<24,19>). An external 100

Ω differential resistor is required between the TX

baseband input pins (TXBBIP and TXBBIN, pins 22 and 21, and TXBBQP and TXBBQN, pins 20 and 19) if

utilizing the dc DAC. The optimum value of the dc DAC, which minimizes carrier leakage, can be read from the

EEPROM within the TRF2443. See the application note (SLWU064) on how to access EEPROM information.

The mixers of the IQ modulator use an external load. The collectors of the output transistors are connected to the

pins MIXINDN and MIXINDP (pins 2 and 3). On the board, a pullup inductor to Vcc must be connected to each of

those pins, as well as a shunt resistor between the pins (see the Application Schematic section).

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TRF2443IPFPR Datasheet(PDF) 55 Page - Texas Instruments

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