Adaptive echo cancellation for RFID systems

A radio-frequency identification (RFID) reader having fast-adaptive echo cancellation for backscatter-modulated signals is described. The echo cancellation includes subtracting an RF-level cancel signal from the received signal, where the cancel signal is generated based upon an error measured in the receive signal after downconversion to baseband and low-pass filtering. The cancel signal is based upon a cumulative sum or integral of error signals and an estimated complex-valued transfer function of the scaling circuit. Methods of quick calibration of the reader are described, including accounting for circuit offsets and determining the estimated complex-valued transfer function.