TCM4400EPET datasheet(30/64 Pages) TI

30 / 64 page

TCM4400E

GSM/DCS BASEBAND AND VOICE A/D

AND D/A RF INTERFACE CIRCUIT

SLWS082A – JULY 1999 – REVISED MARCH 2000

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

auxiliary RF functions

The auxiliary RF functions include the following:

D Automatic frequency control

D Auxiliary analog converter (Automatic gain control)

D RF power control

D Monitoring

Each of these functions is discussed in the following paragraphs.

automatic frequency control (AFC)

The automatic frequency control function consists of a DAC converter optimized for high-resolution dc

conversion. The AFC digital interface includes two registers that can be written using the serial interfaces. The

content of these registers controls a 13-bit DAC, whose purpose is to correct frequency shifts of the oscillator

maintaining the master clock frequency in a 0.1 ppm range.

Optimizing the AFC function depends on the type of oscillator used and whether its sampling frequency is

programmable. This means that the lower the selected frequency the lower the resolution and power

consumption. Using a high-quality resonance oscillator filter permits the AFC circuit to operate at low frequency.

Thus, a low-cost oscillator permits operation at a higher internal frequency to ensure 13-bit resolution.

The AFC value is programmed with registers AUXAFC1, which contains the ten LSBs, and AUXAFC2, which

contains the three MSBs. The three MSBs are sent to the DAC through a shadow register the contents of which

is updated when LSBs are written in AUXAFC1, so proper operation of the AFC is ensured by writing the MSB’s

first and then the LSBs.

Internal resistance and output voltage swing selection are controlled with bit AFZ of AUXCTL2 register. Power

down is controlled with two bits: the first bit, AFCPN of AUXCTL1 register, determines whether the AFC can be

powered down from the external PWRDN terminal; the second bit, AFCPD of AUXCTL1 register, controls the

activation of the the AFC function. See the topic, power-down functional description for more details about

power-down control.

The auxiliary analog functions of the GSM baseband A/D and D/A conversions are independently powered from

the AVDD5 external terminal.

auxiliary analog converter (automatic gain control (AGC))

The auxiliary analog converter control function includes a register which can be written to using the serial

interfaces and a 10-bit D/A converter that provides a control signal to set the gain of the RF section receive

amplifier. The 10-bit D/A converter is accessed through the internal register AUXAGC.

Power down is controlled with two bits. The first bit (AGCW of AUXCTL2 register) determines whether the AGC

can be powered down with the external GSM receive window activation (BDLON). The second bit (AGCPD of

AUXCTL2 register) controls the activation of AGC function. See the topic, power-down functional description

for more details about power-down control.

The auxiliary analog functions of the GSM baseband A/D and D/A conversions are independently powered from

the AVDD5 external terminal.

TCM4400EPET Datasheet(PDF) 30 Page - Texas Instruments

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