| 摘要 |
An impedance matching circuit has comparator, counter, two current sources, semiconductor resistance device, and variable MOS impedance device. The current sources are respectively coupled to an internal impedance device and an external impedance device. The comparator has two input terminals and an output terminal. The input terminals of the comparator are coupled to the internal and external impedance devices. The output terminal of the comparator is coupled to the counter. The variable MOS impedance device is coupled between the counter and the semiconductor impedance, and is controlled by the counter. When the voltages of the internal impedance and the external impedance are not matched, the variable MOS impedance device can provide the compensating impedance by adjusting the counting value of the counter.
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