The invention discloses a
demodulation circuit used for a passive
ultrahigh frequency RFID
label chip. The
demodulation circuit comprises a rectifying circuit, an envelope extraction circuit, a low-pass filtering circuit, a mean value generating circuit, a
comparator, a shaping circuit, an enabling
control circuit and a biasing circuit. The rectifying circuit has a
primary level and an auxiliary level, rectifying is achieved through threshold value compensation, and the envelope extraction circuit extracts envelopes under the control of the enabling
control circuit. The low-pass filtering circuit is directly of an RC structure, and the mean value generating circuit is composed of an
operational amplifier, a
diode and a
capacitor. Mean value generating is achieved based on a
peak detection principle, the
comparator achieves comparing through an open-loop
operational amplifier, the shaping circuit is composed of two cascaded inverters, the mode that three inverters are cascaded is adopted for the enabling
control circuit to control the mean value generating circuit, the
comparator and the shaping circuit, so that
power consumption needed when the
demodulation circuit does not work is greatly lowered, and the biasing circuit provides nA-level currents for the rectifying circuit, the mean value generating circuit and the comparator. The demodulation circuit has the advantages of being high in sensitivity, large in input range, low in
power consumption, small in area and low in cost.