Circuit having high-pass filter with variable corner frequency

An input stage of a chip, comprising:

• an input capacitor, for directly receiving an input signal from a pad of the chip to generate a first signal;
• and
• an amplifier with a feedback resistor and a feedback capacitor, for amplifying the first signal to generate an output signal, wherein the feedback capacitor is a variable feedback capacitor;
• wherein in a first mode, the feedback capacitor is controlled to have the a first capacitance to shorten a settling time of the output signal, and in a second mode, the feedback capacitor is controlled to have a second capacitance greater than the first capacitance.

A circuit, comprising:

• a filter with an amplifier circuit, for filtering and amplifying an input signal to generate an output signal;
• wherein a corner frequency of the filter is adjustable to control a settling time of the output signal;
• wherein the circuit is an input stage of a chip, and the filter directly receives the input signal from a pad of the chip to generate a filtered input signal, and the amplifier circuit amplifies the filtered input signal to generate the output signal;
• wherein the filter comprises a variable resistor, the variable resistor has a first electrode and a second electrode, the first electrode is coupled to the pad of the chip, the second electrode is coupled to an input terminal of the amplifier, and the variable resistor is controlled to have different resistances to make the filter have different corner frequencies.