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PCF50732H/F1 Datasheet PDF : 64 Pages
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Philips Semiconductors
Baseband and audio interface for GSM
Objective specification
PCF50732
8 FUNCTIONAL DESCRIPTION
This chapter gives a brief overview of the device.
The detailed functional description can be found in the
following chapters:
Chapter 9 “Baseband CODEC”
Chapter 10 “Voice band CODEC”
Chapter 11 “Auxiliary functions”
Chapter 12 “Control Serial Interface (CSI)”
Chapter 13 “Voice band Signal Processor (VSP)”.
8.1 General
As low power consumption in mobile telephones is a very
important issue, all the circuit parts in the PCF50732 can
be powered-on/off either by means of the external signals
AUXST, TXON or RXON, or by programming the
respective register bits in the Control Serial Interface
(CSI).
The most important signal for the digital and analog circuit
functions in the PCF50732 is the DAC enable signal
AUXST, which allows to activate AUXDAC1 (AGC) and
AUXDAC2 (AFC), as well as the low-swing master clock
input MCLK. AUXST must be active (HIGH) and VDDA
must be stable (see also Section 18.1) to allow the
master clock to access different circuit parts after a reset
(RESET active). AUXDAC1 and AUXDAC2 are only
activated if their related power-on bit is set. AUXDAC1 is
default off, AUXDAC2 is default on.
RESET must be active during at least 3 MCLK cycles, with
AUXST active, to ensure a correct initialisation of all the
digital circuitry of the PCF50732. Since RESET is
asynchronous even small spikes of a few nanoseconds
can cause partial resets.
For power supply noise interference reduction, a pair of
power supply and ground pins are provided for the:
• Baseband analog: VDDA(bb)/VSSA(bb)
• Voice band analog: VDDA(vb)/VSSA(vb)
• Voice band output drivers: VDDA(vbo)/VSSA(vbo)
• DC reference voltages and currents: VDDA(ref)/VSSA(ref)
• Digital circuitry: VDDD/VSSD.
All VSS pins are connected internally. VDDD is the digital
supply. VDDA(bb), VDDA(vb), VDDA(vbo), and VDDA(ref) are
analog supplies, and are referred to as VDDA throughout
this document. These analog supplies must be connected
externally.
8.2 Baseband and voice band reference voltages
The reference voltage Vref is generated on-chip by a band
gap voltage reference circuit and is available at pin Vref.
As Vref is used as reference for most of the internal analog
circuitry, noise must be kept as low as possible by
connecting an external decoupling capacitor at this pin.
The voltage at Vref is buffered to generate the baseband
and voice band reference voltage Vref as well as internal
references for the different functions, such as the auxiliary
and the transmit DACs.
9 BASEBAND CODEC
The baseband CODEC is a complete interface circuit
between the RF part in a mobile communication handset
and the digital signal processor. It consists of three parts:
• The transmit path, which converts a bitstream to
analog quadrature signals for the RF devices
• The receive path, which transforms the quadrature
signals of the IF chip (I/Q) to digital signals
• The digital baseband serial interface, which
exchanges baseband data between the PCF50732 and
the DSP. The interface also includes signals to
power-up and power-down the baseband transmit
(TX) and receive (RX) paths.
9.1 Baseband transmit path
The baseband transmit path consists of three parts:
• GMSK modulator: generation of a Gaussian Minimum
Shift Keying (GMSK) signal
• 10-bit DACs: digital-to-analog converters for the
I and Q components of the GMSK signal
• Low-pass filters: analog reconstruction low-pass filters
for the output of the DACs.
The requirements of the transmit path of a GSM terminal
are given by “GSM recommendation 05.05”:
• Phase RMS error <5°
• Phase peak error <20°
• Amplitude error < ±1 dB.
Nevertheless the performance of the PCF50732 is far
better than these figures indicate; see Section 18.1.
1999 May 03
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