Patent ID: 7697697

Claim:
An apparatus for automatically determining a type of an external device, comprising: a jack for coupling the external device; an impedance detecting circuit, coupled to the external device through the jack, for generating a first analog signal according to an impedance of the external device and a first resistance, a second analog signal according to the impedance of the external device and a second resistance and a third analog signal according to the impedance of the external device and a third resistance, wherein the first, second and third resistances are different; an analog-to-digital converter, coupled to the impedance detecting circuit, for converting the first, second and third analog signals to first, second and third digital values, respectively; and a control circuit, coupled to the analog-to-digital converter, for determining the type of the external device when the first digital value falls within a first predetermined range, the second digital value falls within a second predetermined range, the third digital value falls within a third predetermined range and all of the first, second and third predetermined ranges together indicate a same recognized condition among a plurality of predetermined recognized conditions; wherein the impedance detecting circuit comprises a plurality of resistors, which couples together in parallel, for providing the first, second and third resistance and each of the first, second and third digital values is a multi-bit number.