Patent ID: 8457183

Claim:
A communication device, comprising: a loop switch, being turned on under a test mode and turned off under a normal mode; a transmitter, coupled to a first end of the loop switch, comprising: a transmitting circuit, for generating at least a detecting signal; and an up converter, for converting the detecting signal to generate a transmitted signal; and a receiver, coupled to a second end of the loop switch, comprising: a low pass filter, for filtering the transmitted signal to generate a filtered signal; a tunable compensation filter, for compensating the filtered signal to generate a received signal; a receiving circuit, for comparing the detecting signal with the received signal to generate at least an indicating signal; and a calibration unit, for adjusting at least a coefficient of the tunable compensation filter according to the indicating signal, wherein the tunable compensation filter has a plurality of poles; the transmitting circuit generates a plurality of detecting signals according to the poles respectively; the receiving circuit compares a plurality of received signals respectively corresponding to the detecting signals with the detecting signals to generate a plurality of indicating signals; and the calibration unit adjusts corresponding coefficients of the tunable compensation filter respectively according to the indicating signals.