This paper presents an architecture for receiver echo cancellation using in-field self-calibration to enable reception of weak signal generated by implanted passive neuron recorders. The echo cancellation enables the use of passive implant transmitter, resulting in low power consumption, and avoids the need for batteries and charge-storage devices at the implant site. A passive, double balanced diode-based mixer architecture is used for the implant transmitter that directly modulates the received carrier with the neuron sensor signal. The transmitted signal is weak compared to the echo that stems from the reflection from the human skull. An echo cancellation scheme is added to the receiver path to suppress the reflected power at transmitted frequency. A built-in-self calibration module defines the characteristic of the cancelling path for each communication cycle. The air gap between transceiver and the brain is assumed to be around 5mm, but variable from measurement to measurement. A receiver with a sensitivity of -123.55 dBm is designed. According to simulations, a neuron potential as low as 27 μVp-p is detectable with an ideal canceller. The echo signal is canceled up to 200 dB for an ideal canceller. The tolerable error for non-ideal canceller is investigated and compared with the ideal case.