Sensor interface devices and amplifiers

1. A sensor interface device, comprising:

a first chopper configured to shift analog input signals from a baseband frequency to a first frequency;

an amplifier configured to amplify the shifted signals;

a bandpass Delta-Sigma A/D converter configured to digitize the amplified signals; and

a second chopper configured to shift the digitized signals from the first frequency back to the baseband frequency.

2. The sensor interface device of claim 1 , wherein the A/D converter is one selected from the group consisting of a real bandpass Delta-Sigma modulator and a complex bandpass Delta-Sigma modulator.

3. The sensor interface device of claim 2 , further comprising:

a decimation filter configured to remove high frequency noises from the shifted signals received from the second chopper.

4. The sensor interface device of claim 1 , wherein the A/D converter is a low-pass Delta-Sigma Modulator.

5. The sensor interface device of claim 4 , further comprising:

a decimation filter configured to filter out high frequency noises from the digitized signals received from the A/D converter,

wherein, the second chopper shifts the filtered signals from the first frequency back to the baseband frequency.

6. The sensor interface device of claim 1 , wherein the amplifier and the A/D converter operate at a second frequency, and wherein the second frequency=n×the first frequency, where n is an integer greater than two.

7. The sensor interface device of claim 1 , wherein the second chopper multiplies the modulated signal by a digital wave with the first frequency to shift the digitized signals from the first frequency back to the baseband frequency.

8. The sensor interface device of claim 7 , further comprising:

a lowpass filter configured to remove a DC-offset noise of the amplifier and the bandpass Delta-Sigma A/D converter from the digitized signals shifted by the second chopper.

9. The sensor interface device of claim 1 , wherein the amplifier comprises an input stage and an output stage, and

wherein the input stage comprises a first pair of capacitors, and the output stage comprises a second pair of capacitors, one of the first pair of capacitors being selectively coupled to one of second pair of capacitors by a set of switches to determine a gain of the amplifier.

10. The sensor interface device of claim 9 , wherein the first chopper comprises a plurality of switches, and wherein the set of switches are controlled to make the first pair of capacitors open-circuited so that no charge injection from the input stage to the output stage occurs at moments when the switches in the first chopper are open.

11. The sensor interface device of claim 10 , wherein the set of switches comprise a first switch coupled to a first capacitor of the first pair of capacitors via a first connection node, a second switch coupled to a second capacitor of the first pair of capacitors via a second connection node, and a third switch and a fourth switch cascaded between the first connection node and the second connection node.

12. The sensor interface device of claim 11 , wherein the output stage comprises an amplifying unit having first and second inputs and two outputs, the first input being coupled to the first switch via a third capacitor, the second input being coupled to second switch via a fourth capacitor.

13. The sensor interface device of claim 12 , wherein the output stage further comprises a fifth capacitor and a sixth capacitor being connected between one of the inputs and a corresponding one of the two outputs, respectively.