Patent ID: 8761384

Claim:
An impedance matching circuit, comprising a peripheral impedance detection module, an analog switch switching module and an impedance matching module that are connected in turn, wherein, the peripheral impedance detection module is set to: detect impedance of a subscriber telephone and output information about the impedance of the subscriber telephone; the analog switch switching module is set to: provide an impedance matching path between the impedance of the subscriber telephone and the impedance matching module according to the information about the impedance of the subscriber telephone output by the peripheral impedance detection module; the impedance matching module is set to: provide a corresponding impedance, through the impedance matching path provided by the analog switch switching module, to match said impedance of the subscriber telephone; wherein, the peripheral impedance detection module comprises an analog to digital conversion (ADC) detection module, and the ADC detection module is set to: output the information about the impedance of the subscriber telephone in the form of high or low level according to a value of the impedance of the subscriber telephone; said ADC detection module comprises a resistor R 0 , a resistor R 1 , a resistor R 2 , a resistor R 3 , a voltage comparator N 1 and a voltage comparator N 2 , wherein, one end of the resistor R 0 is connected to the system power supply Vcc, and the other end of the resistor R 0 is connected to the impedance Rx of the subscriber telephone, as well as negative input ends of the voltage comparator N 1 and the voltage comparator N 2 ; one end of the resistor R 1 is connected to ground, and the other end of the resistor R 1 is connected to a positive input end of the voltage comparator N 1 and the resistor R 2 ; one end of the resistor R 2 is connected to the positive input end of the voltage comparator N 1 and the resistor R 1 , and the other end of the resistor R 2 is connected to the positive input end of the voltage comparator N 2 and the resistor R 3 ; one end of the resistors R 3 is connected to the system power source Vcc and the other end of the resistor R 3 is connected to the positive input end of the voltage comparator N 2 and the resistor R 2 ; the resistor R 1 , the resistor R 2 , and the resistor R 3 are divider resistors and provide reference voltages to the voltage comparators N 1 and N 2 ; the output ends of the voltage comparators N 1 and N 2 are connected to the analog switch switching module, according to the value of the impedance Rx of the subscriber phone , the voltage comparator N 1 and the voltage comparator N 2 output high or low level.