UAA2068G

The UAA2068G BiCMOS device integrates a 950 MHz VCO, a frequency doubler, main and reference dividers and a phase comparator, to implement a phase-locked loop for DECT channel frequencies. The 1.9 GHz signal of UAA2068G is buffered and switched, in TX mode, to drive the transmit power amplifier (CGY20xx series) or, in RX mode, to be used as an LO signal for the receiver mixer IC (UAA2078).

The synthesizer's main divider UAA2068G is driven by the frequency doubler output in the range from 1880 to 1920 MHz and programmed via a 3-wire serial bus.The reference divider ratio is fixed at 8. Outputs of the main and reference dividers drive a phase comparator where a charge pump produces phase error current pulses for integration in an external loop filter. Only a passive loop filter is necessary. The charge-pump current of UAA2068G (phase comparator gain) is set by an external resistor at pin RSET.

The VCO is powered from an internally regulated voltage source and UAA2068G includes internal varicap diodes. Its tuning range is wider than the required band to allow for production spreads. In a TDMA system such as DECT, the VCO and the synthesizer are switched on one slot before the required one to lock the VCO to the required channel frequency. Just before the required slot, the synthesizer is switched off, allowing open-loop modulation of the VCO during transmission. When opening the loop, the frequency pulling (due to switching off the synthesizer) UAA2068G can be maintained within the DECT specification.

The UAA2068G is designed to operate from 3 NiCd cells in pocket phones, with low current and nominal 3.6 V supplies. Separate power and ground pins are provided to the different parts of the circuit. The ground of UAA2068G leads should be short-circuited externally to prevent large currents flowing across the die and thus causing damage.

All supply pins of UAA2068G (V_CC) must also be at the same potential,except V_CC(CP) which can be equal to or greater than the other supply pins (e.g. V_CC = 3 V and V_CC(CP) = 5 V for wider V_CO control voltage range).