Cobba

COBBA GJP ASIC provides an interface between the baseband and the RF-circuitry. COBBA performs analogue to digital conversion of the receive signal. For transmit path COBBA performs digital to analogue conversion of the transmit amplifier power control ramp and the in-phase and quadrature signals. A slow speed digital to analogue converter will provide automatic frequency control (AFC).

COBBA is at any time connected to MAD asic with two interfaces, one for transferring TX and RX data between MAD and COBBA and one for transferring codec RX/TX samples.

Requirements for a real time clock implementation are a basic clock (hours and minutes), a calender and a timer with alarm and power on/off -function and miscellaneous calls. The RTC will contain only the time base and the alarm timer but all other functions (e.g. calendar) will be implemented with the MCU software. The RTC needs a power backup to keep the clock running when the phone battery is disconnected. The backup power is supplied from a rechargable polyacene battery that can keep the clock running some ten minutes. If the backup has expired, the RTC clock restarts after the main battery is connected. The CCONT keeps MCU in reset until the 32kHz source is settled (1s max).

The CCONT is an ideal place for an integrated real time clock as the asic already contains the power up/down functions and a sleep control with the 32kHz sleep clock, which is running always when the phone battery is connected. This sleep clock is used for a time source to a RTC block.

CHAPS has a current limited voltage regulator for charging a backup battery. The regulator derives its power from VOUT so that charging can take place without the need to connect a charger. The backup battery is only used to provide power to a real time clock when VOUT is not present so it is important that power to the charging circuitry is derived from VOUT and that the charging circuitry does not present a load to the backup battery when VOUT is not present.

It should not be possible for charging current to flow from the backup battery into VOUT if VOUT happens to be lower than VBACK. Charging current will gradually diminish as the backup battery voltage reaches that of the regulation voltage.

Real Time Clock

RTC backup battery charging

RF Module

This RF module takes care of all RF functions of EGSM/DCS1800 dualband engine. RF circuitry is located on one side of the 8 layer tranceiver-PCB. PCB area for the Rf circuitry is about 15 cm2. The RF design is based on the first dualband direct conversion RF-IC "Hagar". So there is no intermediate frequency and that means the number of component is much lover than before and there shall be much less interference problems than previously.

EMC emissions are taken care of using metallized plactic shield, which screens the whole transceiver. Internal screening is realized with isolated partitions. At least the VCO is isolated. The baseband circuitry is located on the same side of the same board.

Maximum Ratings

Parameter

Rating

Battery voltage, idle mode

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