DESCRIPTION
The SA900 is a monolithic high performance, multi-function transmit modulator for use in cellular radio applications, fabricated in QUBiC BiCMOS technology. The SA900 features both analog (AMPS) mode and complex, I/Q digital (NADC IS–136) mode quadrature modulation functions, a PLL synthesizer with VCO, crystal oscillator, programmable prescalers and Gilbert cell multiplier phase detector with programmable charge pump output. The DUALTX output can be used in DUAL mode cellular phone applications with the AMPS and NADC modulation being applied to the I/Q baseband inputs. The DUALTX output also provides 6-bit power control with 40dB of gain control in 0.63dB steps. In addition, buffered crystal oscillator programmable prescaler outputs are provided to support system clock reference needs. Programming of the SA900 functions are realized by a high speed 3-wire serial interface. The SA900 can be programmed into a sleep mode (low current mode providing crystal oscillator and Master Clock functions), a standby mode (providing crystal oscillator, Master Clock, System Clock 1 and Transmit LO buffer functions), and the AMPS mode and the DUAL mode configurations.

FEATURES
• VCC = 4.0V
• Tx output frequency = 900MHz
• Direct modulation of RF
• DUAL mode, on-chip PA control
• I/Q modulator
• Single sideband quadrature LO generation with no external
   adjustments required
• On-chip crystal oscillator with 3 buffered outputs
• AMPS/TACS compatible
• On-chip VCO
• Selective power-down
   – Low power AMPS/TACS mode
   – Low power dual mode NADC
• 48-Pin TQFP package

APPLICATIONS
• North American Digital Cellular (TDMA IS-136)