PCF50732 datasheet(21/64 Pages) PHILIPS

21 / 64 page

1999 May 03

Philips Semiconductors

Objective speciﬁcation

Baseband and audio interface for GSM

PCF50732

11 AUXILIARY FUNCTIONS

The auxiliary functions part consists of three

digital-to-analog converters (DACs) and a 4 input

analog-to-digital converter (ADC) with a 12-bit range.

The DACs are for:

• Automatic Gain Control (AGC): AUXDAC1

• Automatic Frequency Control (AFC): AUXDAC2

• Power ramping: AUXDAC3.

11.1

Automatic Gain Control (AGC): AUXDAC1

The AUXDAC1 is an 8-bit binary coded, guaranteed

monotonic digital-to-analog converter.

The status of AUXDAC1 is controlled by the signal AUXST

and a power-up bit in the Power control register. The signal

that switches the external VCXO can also be used to

control the AUXST pin of the PCF50732. The AUXDAC1

output is floating in Power-down mode (AUXST = LOW).

The input MCLK is then deactivated.

When AUXST goes HIGH, AUXDAC1 is powered-up and

the converted value of the corresponding register in the

control register block is available at the AUXDAC1 output

pin.

If a write access to the AUXDAC1 register occurs, the DAC

is activated with the new content of the DAC register (see

Table 14 and 15). The AUXDAC1 must be powered-up by

setting the correct bit in the Power control register. At reset

AUXDAC1 is powered-down.

11.2

Automatic Frequency Control (AFC):

AUXDAC2

The AUXDAC2 is a 12-bit binary coded, guaranteed

monotonic digital-to-analog converter. This DAC is used to

control the frequency of an external master clock VCXO.

The status of AUXDAC2 is controlled by the signal AUXST

and a power-up bit in the Power control register. The signal

that switches the external VCXO can also be used to

control the AUXST pin of the PCF50732. The AUXDAC2

output is floating in Power-down mode (AUXST = LOW).

When AUXST goes HIGH, AUXDAC2 is powered-up and

the converted value of the corresponding register in the

control register block is available at the AUXDAC2 output

pin.

The default value for AUXDAC2 is 1.1 V which

corresponds to a 800H code in the AUXDAC2 register.

At reset AUXDAC2 is powered on.

11.3

Power ramping: AUXDAC3

AUXDAC3 is a 10-bit binary coded digital-to-analog

converter designed for power ramping purposes.

AUXDAC3 is default off. The power ramping behaviour is

described in Section 9.3.2.2.

11.4

Auxiliary analog-to-digital converter (AUXADC)

The AUXADC is specified for voltage and temperature

measurements. It contains 4 input channels required for

∆T and ∆V measurements, as well as battery type

recognition:

•∆T: battery temperature, ambient temperature

(measured across sensor)

•∆V: peak battery voltage, battery voltage during transmit

burst.

Five 12-bit registers are available in which results of

auxiliary analog-to-digital conversions can be stored.

Two registers are dedicated to the input AUXADC1 and

one to each of AUXADC2, AUXADC3 and AUXADC4.

The AUXADC1 input can be used for battery voltage

measurement. In the AUXADC1A register the voltage

during a transmit time slot can be stored. The AUXADC1B

read request to one of these registers is executed by

loading its address into the Read request register, the

actual contents of the addressed register are given to the

control interface and a new measurement is performed in

the next appropriate time slot.

A multiplexer connects each of the AUXADC inputs to a

channel of the receive ADC depending on read access to

the corresponding register.

Thus an auxiliary analog-to-digital conversion is only

possible, if the baseband receive section is not in use

(RXON is LOW). At each read request to one of the

AUXADC registers, a flag is set in the AUXADC flag

be performed. When one of the registers AUXADC1B,

AUXADC2, AUXADC3, or AUXADC4 is being read, the

baseband interface verifies that RXON is LOW, indicating

that no receive burst is currently active. The baseband

receive path is then powered up. After the ADC settling

time has elapsed (see POSTAUXADC in Chapter 18), valid

data is available and stored in the corresponding register.

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