A new TX leakage-suppression technique for an RFID receiver using a dead-zone amplifier

RFID systems use backscattering communication in which the TX transmits a continuous wave (CW) to provide energy to the tag while the RX receives data from it. Due to the simultaneous operation of the RX and TX, large TX leakage is the main issue in securing RX sensitivity. Although external isolation components such as a circulator or directional coupler are widely used in RFID systems, TX leakage is still a dominant source of sensitivity degradation due to its finite isolation and environmentally dependent antenna reflection ratio, as shown in Fig. 5.6.1(a). In a single-antenna-based RFID system, the TX carrier leakage is typically above 0dBm at the RX input despite off-chip isolation components [1]. As can be seen in Fig. 5.6.1(b), when the close-in phase noise of the TX carrier is -85dBc/Hz, the phase noise level of 0dBm TX leakage in the receive channel reaches 89dB higher than the thermal noise level, thus directly degrading the SNR. In efforts to solve the leakage problem, leakage cancellation [2,3] and self-correlated RX [4] techniques have been reported. However, high power consumption for leakage replica generation and long calibration time, as in [2,3], and hardware complexity for a 45 degree phase shift [4] are issues that need to be resolved.