Patent ID: 7439860
Filing Date: 2008-10-21
Classification: G06K

Abstract:
1. A reader for an RFID system comprising: an antenna assembly including an antenna tuning circuit and an antenna, said antenna tuning circuit coupled to said antenna and said antenna having an antenna impedance, wherein said antenna is operated by an AC signal; a variable capacitance circuit included in said antenna tuning circuit, said variable capacitance circuit having at least one variable capacitance element that is reversed biased and comprises a DC bias voltage that is smaller in magnitude than said AC signal; a signal driver coupled to said antenna assembly to apply a drive signal to said antenna, said signal driver having a signal driver impedance; and a controller coupled to said antenna assembly to determine a difference between said antenna impedance and said signal driver impedance and to set said at least one variable capacitance element to a set capacitance value to reduce said difference.