Techniques provided herein are directed toward providing a robust pulse width modulated (PWM) amplitude modulation scheme that enables medical implants with highly inaccurate LOs to reliably receive downlink communications from an interrogator device by using pulse width to encode data. Synchronization and data fields can comprise pulse pairs, distinguishable by medical implants from a ratio of the duration of a long pulse to the duration of a short pulse within the pulse pair. Thus, synchronization can be easily and robustly obtained
