| 摘要 |
The present application relates to a near field communications (NFC) reader which includes an amplifier that drives an antenna. Capacitors of fixed value are connected in series between differential outputs of the amplifier and inputs of the antenna and form a series resonant circuit with the impedance of the antenna. Variable capacitances are provided in series with the fixed value capacitors, and the capacitance of these variable capacitances can be adjusted to compensate for manufacturing tolerances in the fixed value capacitors which cause a frequency offset between a desired resonant frequency of the series resonant circuit its actual resonant frequency, and to compensate for changes in the input impedance of the antenna that occur as the distance between the antenna of the reader and an antenna of an NFC tag changes. |
