A loop filter for a sigma delta modulation device, the loop filter comprising:
- an operational amplifier;
- a circuit including a plurality of capacitors, a plurality of resistors, and a plurality of switches, which are connected to the operational amplifier;
- a memory configured to store one or more instructions;
- and
- a processor configured to execute the one or more instructions stored in the memory, wherein the one or more instructions, when executed by the processor, cause the processor to;
- control turn on or off of the plurality of switches so as to represent signal transfer characteristics of the loop filter for satisfying a third-order transfer function or a second-order transfer function, and to adjust resistor values in an equivalent circuit of the loop filter in order to compensate a notch frequency reduced in the loop filter for satisfying the second-order transfer function,
- wherein the circuit includes:
- a first resistor to which an input signal of the loop filter is applied at a first end thereof and which is connected at a second end thereof to an input terminal of the operational amplifier;
- a first capacitor connecting the first resistor and an input terminal of the operational amplifier;
- a second capacitor connected in series to the first capacitor;
- a third capacitor connected in series to the second capacitor;
- a second resistor, a fourth resistor, and a sixth resistor connected at first ends thereof to a first node that is a node between the first capacitor and the second capacitor;
- and
- a third resistor, a fifth resistor, and a seventh resistor connected at first ends thereof to a second node that is a node between the second capacitor and the third capacitor,
- wherein the circuit further comprises:
- a first switch connected between the first node and the sixth resistor;
- a second switch connected between the second node and the seventh resistor;
- a third switch connected to the first node and the input terminal of the operational amplifier and configured in parallel with the first capacitor;
- and
- a fourth switch connected between the first node and the second resistor,
- wherein the plurality of resistors includes the third resistor and a first additional resistor connected to the third resistor in parallel,
- wherein the circuit includes a fifth switch connected to a first end of the first additional resistor, and
- wherein the processor is configured to control turn on the fifth switch when the loop filter is set to satisfy the second-order transfer function.