| 摘要 |
A circuit and method are disclosed for receiving a digital input signal referenced to arbitrary logic levels, and re-referencing the digital input signal to local logic levels. A re-referencing circuit includes a non-inverting circuit having an input and an output, and a non-inverting transfer characteristic between the input and the output. A capacitive element is connected in series with the non-inverting circuit that capacitively couples the digital input signal to the input of the non-inverting circuit. The re-referencing circuit also includes a resistive element connected between the input and the output of the non-inverting circuit. During operation, rising and falling edges of the digital input signal capacitively couple to the input of the non-inverting circuit and cross a threshold level, causing the non-inverting circuit to change its output state. The voltage at the output of the non-inverting circuit resistively couples back to the input of the non-inverting circuit, where it tends to cause the voltage at the input of the non-inverting circuit to equal the voltage at the output. As the input of the non-inverting circuit has no direct current (DC) connection to the digital input signal, voltage levels at the input of the non-inverting circuit remain referenced to the supply voltages of the non-inverting circuit, regardless of the voltage levels of the digital input signal. A clamping circuit can be used to protect the non-inverting circuit against input voltages having large voltage swings. In addition, an second resistive element can be connected between the input of the non-inverting circuit and a DC level to attenuate feedback from the output of the non-inverting circuit, thereby allowing operation with input signals having small voltage swings.
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