Signal modulating device capable of reducing peaking in signal transfer function

1. A signal modulating device, comprising:

an integrating circuit, arranged to generate an integrated signal according to a scaled analog signal and a first feedback signal;

a resonating circuit, arranged to generate a resonating signal according to the integrated signal;

a first signal converting circuit, arranged to convert the resonating signal into a digital output signal;

a second signal converting circuit, arranged to convert the digital output signal into the first feedback signal;

a first impedance circuit, having a first terminal receiving an analog signal and a second terminal coupled to the resonating circuit for altering the location of zeros in the forward-path transfer function and consequently shaping the signal transfer function (STF) of the signal modulating device; and

a second impedance circuit, having a first terminal receiving the analog signal and a second terminal coupled to the integrating circuit for generating the scaled analog signal.

2. The signal modulating device of claim 1 , wherein the second impedance circuit is a resistor.

3. The signal modulating device of claim 1 , wherein the integrating circuit comprises:

a combining circuit, arranged to generate a combining signal according to the scaled analog signal and the first feedback signal; and

an integrator, arranged to integrate the combining signal to generate the integrated signal.

4. The signal modulating device of claim 3 , wherein the combining signal is a difference between the scaled analog signal and the first feedback signal.

5. The signal modulating device of claim 3 , wherein the integrator comprises:

an amplifying circuit, having a first input terminal receiving the combining signal and a second input terminal coupled to a reference voltage; and

a capacitor, having a first terminal coupled to the first input terminal of the amplifying circuit and a second terminal coupled to an output terminal of the amplifying circuit;

wherein the output terminal of the amplifying circuit is arranged to output the integrated signal.

6. The signal modulating device of claim 1 , wherein the resonating circuit comprises:

an amplifying circuit, having an output terminal for outputting the resonating signal;

a first feedback circuit, coupled between a first input terminal of the amplifying circuit and the output terminal of the amplifying circuit;

a second feedback circuit, coupled between the first input terminal of the amplifying circuit and the output terminal of the amplifying circuit; and

a gain-adjusting circuit, having a first input terminal for receiving the integrated signal, a second input terminal coupled to a reference voltage, a first output terminal coupled to the first input terminal of the amplifying circuit, a second output terminal coupled to the intermediate terminal of the first feedback circuit, and a third output terminal coupled to the intermediate terminal of the second feedback circuit;

wherein the equivalent impedance on the intermediate terminal of the first feedback circuit substantially equals the equivalent impedance on the intermediate terminal of the second feedback circuit, and the gain-adjusting circuit is arranged to tune the transfer gain from the integrated signal to the resonating signal, and the amplifying circuit further comprises a second input terminal, and the second input terminal is coupled to a reference voltage.

7. The signal modulating device of claim 6 , wherein the first feedback circuit comprises:

a first resistor, having a first terminal coupled to the first input terminal of the amplifying circuit;

a second resistor, having a first terminal coupled to a second terminal of the first resistor, and a second terminal coupled to the output terminal of the amplifying circuit; and

a first capacitor, having a first terminal coupled to the second terminal of the first resistor, and a second terminal coupled to a reference voltage;

wherein the second terminal of the first resistor is the intermediate terminal of the first feedback circuit.

8. The signal modulating device of claim 7 , wherein the second feedback circuit comprises:

a second capacitor, having a first terminal coupled to the first input terminal of the amplifying circuit;

a third capacitor, having a first terminal coupled to a second terminal of the second capacitor, and a second terminal coupled to the output terminal of the amplifying circuit; and

a third resistor, having a first terminal coupled to the second terminal of the second capacitor, and a second terminal coupled to the reference voltage;

wherein the second terminal of the second capacitor is the intermediate terminal of the second feedback circuit.

9. The signal modulating device of claim 8 , wherein the gain-adjusting circuit comprises:

a fourth resistor, having a first terminal for receiving the integrated signal, and a second terminal coupled to the first input terminal of the amplifying circuit;

a fourth capacitor, having a first terminal for receiving the integrated signal, and a second terminal coupled to the first input terminal of the amplifying circuit;

a fifth capacitor, having a first terminal for receiving the integrated signal, and a second terminal coupled to the second terminal of the second capacitor; and

a fifth resistor, having a first terminal coupled to the reference voltage, and a second terminal coupled to the second terminal of the first resistor.

10. The signal modulating device of claim 8 , wherein the gain-adjusting circuit comprises:

a fourth resistor, having a first terminal for receiving the integrated signal, and a second terminal coupled to the first input terminal of the amplifying circuit;

a fourth capacitor, having a first terminal for receiving the integrated signal, and a second terminal coupled to the first input terminal of the amplifying circuit;

a fifth resistor, having a first terminal for receiving the integrated signal;

a fifth capacitor, having a first terminal coupled to a second terminal of the fifth resistor, and a second terminal coupled to the first input terminal of the amplifying circuit;

a sixth capacitor, having a first terminal coupled to the reference voltage, and a second terminal coupled to the second terminal of the second capacitor; and

a sixth resistor, having a first terminal coupled to the reference voltage, and a second terminal coupled to the second terminal of the first resistor.

11. The signal modulating device of claim 6 , wherein the first impedance circuit comprises:

a resistor, having a first terminal for receiving the analog signal, and a second terminal coupled to the first input terminal of the amplifying circuit.

12. The signal modulating device of claim 11 , wherein the first impedance circuit further comprises:

a capacitor, having a first terminal for receiving the analog signal, and a second terminal coupled to the first input terminal of the amplifying circuit.

13. The signal modulating device of claim 1 , wherein the first signal converting circuit comprises:

a combining circuit, arranged to generate a combining signal according to the resonating signal and a second feedback signal;

a quantizer, arranged to generate the digital output signal according to the combining signal and a clock signal;

a delay circuit, arranged to delay the digital output signal to generate a delayed signal; and

a digital-to-analog converter, arranged to generate the second feedback signal according to the delayed signal.

14. The signal modulating device of claim 13 , wherein the combining signal is a difference between the resonating signal and the second feedback signal.

15. The signal modulating device of claim 14 , wherein the second signal converting circuit is a digital-to-analog converter, arranged to generate the first feedback signal according to the digital output signal of the first signal converting circuit.

16. The signal modulating device of claim 1 , which is a continuous-time sigma-delta modulator.