Amplitude Shift Keying Demodulator and Radio Frequency Identification System using the same

An amplitude shift keying demodulator adapted to demodulate an alternating current input signal and generate a demodulated envelope signal, the amplitude shift keying demodulator comprising:

• a signal input terminal group comprising a first input terminal and a second input terminal, the signal input terminal group adapted to receive the alternating current input signal;
• an input rectifier circuit comprising:
• a first N-type transistor having a gate electrode, a first source/drain electrode and a second source/drain electrode, wherein the gate electrode of the first N-type transistor is adapted to receive a first control voltage, and the first source/drain electrode of the first N-type transistor is electrically coupled to the first input terminal;
• a second N-type transistor having a gate electrode, a first source/drain electrode and a second source/drain electrode, wherein the gate electrode of the second N-type transistor is adapted to receive the first control voltage, and the first source/drain electrode of the second N-type transistor is electrically coupled to the second input terminal;
• a first P-type transistor having a gate electrode, a first source/drain electrode and a second source/drain electrode, wherein the gate electrode of the first P-type transistor is adapted to receive a second control voltage, and the first source/drain electrode of the first P-type transistor is electrically coupled to the first input terminal;
• and
• a second P-type transistor having a gate electrode, a first source/drain electrode and a second source/drain electrode, wherein the gate electrode of the second P-type transistor is adapted to receive the second control voltage, and the first source/drain electrode of the second P-type transistor is electrically coupled to the second input terminal;
• a current mirror circuit electrically coupled to the input rectifier circuit and adapted to generate a mirror current according to an input current from the input rectifier circuit;
• an output stage electrically coupled to the current mirror circuit to receive the mirror current and adapted to generate an output current according to the mirror current;
• and
• a low pass filter electrically coupled to the output stage to receive the output current and adapted to perform a low pass filtering operation applied to the output current to generate the demodulated envelope signal.