AFE032 datasheet(19/77 Pages) TI1

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Programmable

Filter

DAC

Digital Interface

(SPI)

SCLK

DIN

DOUT

TX PGA

Power Amplifier

TX_F_OUT

TX_PGA_IN

DAC_OUT

XCLK

PA_IN

PA_OUT2

PA_OUT1

1 k:

ZIN

17 k:

CDAC

CIN

Inside the Device

LIM

1.2 V

16.320 kW

+ R

INT

SET

AFE032

www.ti.com

SBOS669A – AUGUST 2013 – REVISED DECEMBER 2013

PA Current Limiting

The PA_ISET pin (pin 26) provides a resistor-programmable output current limit for the PA block. Equation 2

determines the value of the external RSET resistor attached to this pin.

where:

•

RSET = the value of the external resistor connected between pin 26 and ground,

•

RINT = the value of the internal resistor as programmed by the SPI interface in Table 18 (bits 4 and 5), and

•

Ilim = the value of the desired current limit for the PA.

(2)

RINT bit setting for bits 4 and 5 in Table 18 are listed in Table 1.

Table 1. RINT Bit Settings

BIT SETTING

RINT VALUE

17 k

11 k

8 k

1.2 k

Note that there is a 30% tolerance on the Ilim value given by Equation 2.

Tx Block

The Tx block consists of the Tx PGA and Tx filter.

The Tx PGA is a low-noise, high-performance, programmable gain amplifier. In DAC mode [where the DAC pin,

pin 7, is a logic '1' and Tx enable (bit 4 in the REG_RX/TX_CTL register) is a logic '1'], the Tx PGA operates as

the internal digital-to-analog converter (DAC) output buffer with programmable gain. The Tx PGA gain is

programmed through the serial interface. The Tx PGA gain settings are 1.15 V/V, 2.3 V/V, 3.25 V/V, and 4.6 V/V.

Gain is selectable via the TX_PGA gain pins (bits 2 to 0 in the REG_RX/TX_CTL register).

The Tx filter is a unity-gain, fourth-order, low-pass filter. The Tx filter cutoff frequency is selectable between the

CENELEC (bands A, B, C, or D), ARIB, or FCC modes. The LPF band select bits (bits 6 to 4 in the

REG_HPF/LPF_CFG register) determine the cutoff frequency.

When in DAC mode, the device accepts serial data from the microprocessor and writes that data to the internal

DAC registers.

Proper connections for the Tx signal path for DAC mode operation are shown in Figure 14.

(1) For the capacitor value of CIN, fHP is the desired lower cutoff frequency and 17 kΩ is the PA input resistance.

Figure 14. Recommended Tx Signal Chain Connections

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