GENERAL DESCRIPTION
The PCF7991AT is a fully integrated Advanced Basestation IC, ABIC, designed for car immobilizer systems providing read and write access to an identification transponder. The device is intended for use with the Philips transponder family (PCF79xx) as well as other transponder types operating at 125 kHz and employing ASK, Amplitude Shift Keying for write and AM/PM for the read operation. The receiver characteristics (amplifier gain, filter cutoff frequencies) can be optimized to system and transponder requirements. The PCF7991AT IC is designed for easy integration into immobilizer read/write and read-only systems featuring a high degree of integration and very low external component count. The device integrates a powerful antenna driver/modulator, a low-noise adaptive sampling time demodulator, programmable filters/amplifier and digitizer, required to design high-performance basestations. A three wire microcontroller interface is provided for programming the PCF7991AT as well as for the bidirectional communication with the transponder. The three-wire interface can be configured for two wire operation by connecting the data input and the data output.
The device employs a unique Adaptive Sampling Time (AST) demodulation technique, that extends the system operation range and eliminates the effect of a zero amplitude modulation response from the transponder, as a result of resonance frequency tolerances.

FEATURES
• Fully integrated single chip basestation
• Compatible with PCF79xx transponder family
• Robust antenna coil power driver stage with modulator
• High performance adaptive sampling time AM/PM
   demodulator (patent pending)
• Read and write function
• Programmable modulator/demodulator characteristics
• On-chip clock oscillator and divider in the case of
   external clock reference
• Antenna rupture and short circuit detection
• Low power consumption
• Very low power stand-by mode
• Low external component count
• Small package (SO14).