Active load generation circuit and filter using same

1. An active load generation circuit comprising:

a transistor that provides an impedance and has a control terminal and an input terminal, wherein the control terminal receives a control voltage, the input terminal receives an input signal, and the impedance is related to the control voltage;

a voltage control circuit configured to generate an intermediate voltage according to a power supply voltage and a first reference voltage;

a voltage offset and tracking circuit coupled between the voltage control circuit and the transistor and configured to generate the control voltage according to the input signal and the intermediate voltage, wherein the control voltage varies with the input signal; and

a temperature sensing circuit coupled to the voltage control circuit and configured to sense an ambient temperature of the active load generation circuit and adjust the first reference voltage according to the ambient temperature.

2. The active load generation circuit of claim 1 , wherein the transistor is a first transistor, the control terminal is a first control terminal, and the voltage control circuit comprises:

a second transistor having a second control terminal and an output terminal, wherein the output terminal of the second transistor outputs the intermediate voltage;

a plurality of resistors connected in series between the second transistor and the power supply voltage, or between the second transistor and a second reference voltage; and

an operational amplifier having a first input terminal, a second input terminal, and an output terminal, wherein the first input terminal receives the first reference voltage, the second input terminal is coupled to the resistors, and the output terminal of the operational amplifier is coupled to the second control terminal.

3. The active load generation circuit of claim 2 , wherein the first transistor is a P-type metal-oxide-semiconductor field-effect transistor (MOSFET); wherein when the ambient temperature increases, the temperature sensing circuit increases the first reference voltage, and when the ambient temperature decreases, the temperature sensing circuit decreases the first reference voltage.

4. The active load generation circuit of claim 2 , wherein the first transistor is an N-type metal-oxide-semiconductor field-effect transistor (MOSFET); wherein when the ambient temperature increases, the temperature sensing circuit decreases the first reference voltage, and when the ambient temperature decreases, the temperature sensing circuit increases the first reference voltage.

5. The active load generation circuit of claim 2 , wherein the power supply voltage can be positive, zero, or negative, and the second reference voltage can be positive, zero, or negative.

6. The active load generation circuit of claim 1 further comprising:

a voltage detecting circuit coupled to the voltage control circuit and configured to detect the power supply voltage to generate a control value;

wherein the voltage control circuit adjusts the intermediate voltage according to the control value.

7. The active load generation circuit of claim 6 , wherein the voltage detecting circuit comprises:

a plurality of resistors connected in series between the power supply voltage and a second reference voltage and configured to generate a plurality of divided voltages according to the power supply voltage and the second reference voltage; and

a plurality of comparators coupled to the resistors and configured to generate the control value by comparing the divided voltages with a predetermined voltage.

8. The active load generation circuit of claim 1 , wherein the voltage offset and tracking circuit comprises:

an amplifying circuit configured to amplify a difference between the intermediate voltage and a common mode voltage of the input signal to generate an amplified voltage; and

an adding circuit coupled to the amplifying circuit and configured to add the amplified voltage and the input signal to thereby generate the control voltage.

9. An active load generation circuit comprising:

a first transistor that provides an impedance and has a first control terminal, wherein the first control terminal receives a control voltage, and the impedance is related to the control voltage;

a voltage control circuit coupled to the first transistor and configured to generate the control voltage according to a power supply voltage and a first reference voltage, the voltage control circuit comprising:

a second transistor having a second control terminal and a first output terminal, wherein the first output terminal outputs the control voltage;

a plurality of resistors connected in series between the second transistor and the power supply voltage, or between the second transistor and a second reference voltage; and

an operational amplifier having a first input terminal, a second input terminal, and a second output terminal, wherein the first input terminal receives the first reference voltage, the second input terminal is coupled to the resistors, and the second output terminal is coupled to the second control terminal; and

a temperature sensing circuit coupled to the voltage control circuit and configured to sense an ambient temperature of the active load generation circuit and adjust the first reference voltage according to the ambient temperature.

10. The active load generation circuit of claim 9 , wherein the first transistor is a P-type metal-oxide-semiconductor field-effect transistor (MOSFET); wherein when the ambient temperature increases, the temperature sensing circuit increases the first reference voltage, and when the ambient temperature decreases, the temperature sensing circuit decreases the first reference voltage.

11. The active load generation circuit of claim 9 , wherein the first transistor is an N-type metal-oxide-semiconductor field-effect transistor (MOSFET); wherein when the ambient temperature increases, the temperature sensing circuit decreases the first reference voltage, and when the ambient temperature decreases, the temperature sensing circuit increases the first reference voltage.

12. The active load generation circuit of claim 9 further comprising:

a voltage detecting circuit coupled to the voltage control circuit and configured to detect the power supply voltage to generate a control value;

wherein the voltage control circuit adjusts the control voltage according to the control value.

13. The active load generation circuit of claim 12 , wherein the resistors are first resistors, and the voltage detecting circuit comprises:

a plurality of second resistors connected in series between the power supply voltage and the second reference voltage and configured to generate a plurality of divided voltages according to the power supply voltage and the second reference voltage; and

a plurality of comparators coupled to the second resistors and configured to generate the control value by comparing the divided voltages with a predetermined voltage.

14. An active load generation circuit comprising:

a transistor that provides an impedance and has a control terminal, wherein the control terminal receives a control voltage, and the impedance is related to the control voltage;

a voltage control circuit coupled to the transistor and configured to generate the control voltage according to a power supply voltage and a first reference voltage;

a temperature sensing circuit coupled to the voltage control circuit and configured to sense an ambient temperature of the active load generation circuit and adjust the first reference voltage according to the ambient temperature;

a voltage detecting circuit coupled to the voltage control circuit and configured to detect the power supply voltage to generate a control value;

wherein the voltage control circuit adjusts the control voltage according to the control value.

15. The active load generation circuit of claim 14 , wherein the voltage detecting circuit comprises:

a plurality of resistors connected in series between the power supply voltage and a second reference voltage and configured to generate a plurality of divided voltages according to the power supply voltage and the second reference voltage; and

a plurality of comparators coupled to the resistors and configured to generate the control value by comparing the divided voltages with a predetermined voltage.

16. The active load generation circuit of claim 14 , wherein the transistor is a first transistor, the control terminal is a first control terminal, and the voltage control circuit comprises:

a second transistor having a second control terminal and a first output terminal, wherein the first output terminal outputs the control voltage;

a plurality of resistors connected in series between the second transistor and the power supply voltage, or between the second transistor and a second reference voltage; and

an operational amplifier having a first input terminal, a second input terminal, and a second output terminal, wherein the first input terminal receives the first reference voltage, the second input terminal is coupled to the resistors, and the second output terminal is coupled to the second control terminal;

wherein the first transistor is a P-type metal-oxide-semiconductor field-effect transistor (MOSFET);

wherein when the ambient temperature increases, the temperature sensing circuit increases the first reference voltage, and when the ambient temperature decreases, the temperature sensing circuit decreases the first reference voltage.

17. The active load generation circuit of claim 14 , wherein the transistor is a first transistor, the control terminal is a first control terminal, and the voltage control circuit comprises:

a second transistor having a second control terminal and a first output terminal, wherein the first output terminal outputs the control voltage;

a plurality of resistors connected in series between the second transistor and the power supply voltage, or between the second transistor and a second reference voltage; and

an operational amplifier having a first input terminal, a second input terminal, and a second output terminal, wherein the first input terminal receives the first reference voltage, the second input terminal is coupled to the resistors, and the second output terminal is coupled to the second control terminal;

wherein the first transistor is an N-type metal-oxide-semiconductor field-effect transistor (MOSFET);

wherein when the ambient temperature increases, the temperature sensing circuit decreases the first reference voltage, and when the ambient temperature decreases, the temperature sensing circuit increases the first reference voltage.