Reader and rfid reader

An RFID reader, comprising:

• a power amplifier, configured to output a first Radio Frequency (RF) transmission signal;
• a low-noise amplifier, configured to transmit a first RF response signal according to the first RF transmission signal, wherein the first RF response signal carries an upper-tag signal and a lower-tag signal and the first RF transmission signal has the same RF frequency as the first RF response signal;
• a mixer, coupled to the low-noise amplifier, configured to down-convert the first RF response signal;
• a selectable filter, coupled to the mixer, configured to filter the down-convert upper-tag and lower-tag signals, and select a clearer one from the filtered upper-tag and lower-tag signals to output;
• a circulator, coupled between the power amplifier and the low-noise amplifier, configured to transmit the first RF transmission signal to an RF connection node or receive the first RF response signal from the RF connection node,
• an automatic-matching-and-tuning circuit, coupled to the circulator, configured to perform impedance matching between the RF connection node and the circulator;
• and
• a control circuit, coupled to the automatic-matching-and-tuning circuit, configured to adjust the automatic-matching-and-tuning circuit to perform impedance matching between the RF connection node and the circulator.