| 摘要 |
The invention provides adaptive threshold circuits for comparators, whereby the threshold voltage adapts to characteristics of the input signal. In one embodiment, the steady-state threshold voltage stored on a peak-detector capacitor is generated by ratioing the base-emitter voltages of two emitter-follower transistors. As the input signal varies, the threshold voltage follows the input signal. Voltage-controlled current sources sense the amplitude of the input signal, and adjust the amplitude of the threshold voltage by controlling the voltage dropped across a resistor. A feedback signal that indicates the state of the comparator output is coupled to the adaptive threshold circuit to provide hysteresis. In another embodiment, the threshold voltage is determined by the voltage drop across a first resistor. Voltage-controlled current sources sense the amplitude of the input signal, and adjust the amplitude of the threshold voltage by controlling the voltage dropped across a second resistor.
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