Feedback LNA with image filtering

1. A system, comprising:

a clock generator configured to generate a clock signal having a frequency of |f bp +f i |;

a mixer configured to input (1) an input signal that includes a desired signal at the frequency f i and (2) the clock signal and generate a mixed signal using the input signal and the clock signal;

a filter, having a bandpass region that includes the frequency f bp that is higher in frequency than f i , configured to input the mixed signal and generate a filtered signal based at least in part on the bandpass region; and

a controller configured to set f bp to be greater than 0.5*f e −1.5*f i — min +0.25*f bw , wherein the input signal includes an undesired signal in the frequency range −f e to +f e , f i — min is a minimum input signal frequency, and f bw is the bandwidth of the bandpass region of the filter.

2. The system of claim 1 , wherein:

the filter is programmable and the bandpass region, including the frequency f bp , is able to be adjusted; and

the clock generator is programmable and is adjusted such that the clock signal generated has the frequency |f bp +f i | based at least in part on the value that the frequency f bp is set to.

3. The system of claim 1 , wherein:

the clock generator and the filter are adjustable; and

the adjustable clock generator, the mixer, and the adjustable filter are differential and each has a positive and a negative input and a positive and a negative output.

4. The system of claim 1 , wherein the clock generator is a first clock generator, the mixer is a first mixer, and the system further includes:

a second clock generator configured to generate a second clock signal having a frequency of |f bp +f i |; and

a second mixer configured to input (1) the filtered signal and (2) the second clock signal and generate a second mixed signal using the filtered signal and the second clock signal.

5. A system, comprising:

a first clock generator configured to generate a clock signal having a frequency of |f bp +f i |;

a first mixer configured to input (1) an input signal that includes a desired signal at the frequency f i and (2) the clock signal and generate a mixed signal using the input signal and the clock signal;

a first filter, having a bandpass region that includes the frequency f bp , configured to input the mixed signal and generate a filtered signal based at least in part on the bandpass region;

a second clock generator configured to generate a second clock signal having a frequency of |f bp +f i |;

a second mixer configured to input (1) the filtered signal and (2) the second clock signal and generate a second mixed signal using the filtered signal and the second clock signal;

a first transconductance element, wherein the output of the first transconductance element is coupled to the input of the first mixer;

a second transconductance element, wherein the input of the second transconductance element is coupled to the output of the second mixer;

a first feedback element, wherein a first connection of the first feedback element is coupled to the input of the first transconductance element and a second connection of the first feedback element is coupled to the output of the second transconductance element;

a second feedback element, wherein a first connection of the second feedback element is coupled to the output of the first transconductance element and a second connection of the second feedback element is coupled to the output of the second transconductance element; and

a third feedback element, wherein a first connection of the third feedback element is coupled to the input of the second transconductance element and a second connection of the third feedback element is coupled to the output of the second transconductance element.

6. The system of claim 5 , wherein:

the first and second transconductance elements and the first, second, and third feedback elements are differential and each has a positive and a negative input and a positive and a negative output;

the first feedback element includes a first negative feedback element, wherein a first connection of the first negative feedback element is coupled to the positive input of the first transconductance element and a second connection of the first negative feedback element is coupled to the positive output of the second transconductance element;

the first feedback element includes a second negative feedback element, wherein a first connection of the second negative feedback element is coupled to the negative input of the first transconductance element and a second connection of the second negative feedback element is coupled to the negative output of the second transconductance element;

the second feedback element includes a third negative feedback element, wherein a first connection of the third negative feedback element is coupled to the positive output of the first transconductance element and a second connection of the third negative feedback element is coupled to the positive output of the second transconductance element;

the second feedback element includes a fourth negative feedback element, wherein a first connection of the fourth negative feedback element is coupled to the negative output of the first transconductance element and a second connection of the fourth negative feedback element is coupled to the negative output of the second transconductance element;

the third feedback element includes a fifth negative feedback element, wherein a first connection of the fifth negative feedback element is coupled to the negative input of the second transconductance element and a second connection of the fifth negative feedback element is coupled to the positive output of the second transconductance element; and

the third feedback element includes a sixth negative feedback element, wherein a first connection of the sixth negative feedback element is coupled to the positive input of the second transconductance element and a second connection of the sixth negative feedback element is coupled to the negative output of the second transconductance element.

7. The system of claim 5 , wherein at least one of the first, second, or third feedback elements includes a resistor.

8. The system of claim 5 , wherein at least one of the first, second, or third feedback elements includes a capacitor.

9. The system of claim 5 , wherein at least one of the first, second, or third feedback elements includes an inductor.

10. The system of claim 5 , wherein the frequency f bp is higher in frequency than f i .

11. A method, comprising:

using a clock generator to generate a clock signal having a frequency of |f bp +f i |;

using a mixer to input (1) an input signal that includes a desired signal at the frequency f i and (2) the clock signal and generate a mixed signal using the input signal and the clock signal;

using a filter having a bandpass region that includes the frequency f bp that is higher in frequency than f i to filter the mixed signal in order to generate a filtered signal based at least in part on the bandpass region; and

setting f bp to be greater than 0.5*f e −1.5*f i — min +0.25*f bw , wherein the input signal includes an undesired signal in the frequency range −f e to +f e , f i — min is a minimum input signal frequency, and f bw is the bandwidth of the bandpass region of the filter.

12. The method of claim 11 , wherein:

the filter is programmable and the bandpass region, including the frequency f bp , is able to be adjusted; and

the clock generator is programmable and is adjusted such that the clock signal generated has the frequency |f bp +f i | based at least in part on the value that the frequency f bp is set to.

13. The method of claim 11 , wherein:

the clock generator and the filter are adjustable; and

the adjustable clock generator, the mixer, and the adjustable filter are differential and each has a positive and a negative input and a positive and a negative output.

14. The method of claim 11 , wherein the clock generator is a first clock generator, the mixer is a first mixer, and the method further includes:

using a second clock generator to generate a second clock signal having a frequency of |f bp +f i |; and

using a second mixer to input (1) the filtered signal and (2) the second clock signal and generate a second mixed signal using the filtered signal and the second clock signal.

15. A method, comprising:

using a first clock generator to generate a clock signal having a frequency of |f bp +f i |;

using a first mixer to input (1) an input signal that includes a desired signal at the frequency f i and (2) the clock signal and generate a mixed signal using the input signal and the clock signal;

using a first filter having a bandpass region that includes the frequency f bp to filter the mixed signal in order to generate a filtered signal based at least in part on the bandpass region;

using a second clock generator to generate a second clock signal having a frequency of |f bp +f i |; and

using a second mixer to input (1) the filtered signal and (2) the second clock signal and generate a second mixed signal using the filtered signal and the second clock signal, wherein:

there is a first transconductance element, where the output of the first transconductance element is coupled to the input of the first mixer;

there is a second transconductance element, where the input of the second transconductance element is coupled to the output of the second mixer;

there is a first feedback element, where a first connection of the first feedback element is coupled to the input of the first transconductance element and a second connection of the first feedback element is coupled to the output of the second transconductance element;

there is a second feedback element, where a first connection of the second feedback element is coupled to the output of the first transconductance element and a second connection of the second feedback element is coupled to the output of the second transconductance element; and

there is a third feedback element, where a first connection of the third feedback element is coupled to the input of the second transconductance element and a second connection of the third feedback element is coupled to the output of the second transconductance element.

16. The method of claim 15 , wherein:

the first and second transconductance elements and the first, second, and third feedback elements are differential and each has a positive and a negative input and a positive and a negative output;

the first feedback element includes a first negative feedback element, wherein a first connection of the first negative feedback element is coupled to the positive input of the first transconductance element and a second connection of the first negative feedback element is coupled to the positive output of the second transconductance element;

the first feedback element includes a second negative feedback element, wherein a first connection of the second negative feedback element is coupled to the negative input of the first transconductance element and a second connection of the second negative feedback element is coupled to the negative output of the second transconductance element;

the second feedback element includes a third negative feedback element, wherein a first connection of the third negative feedback element is coupled to the positive output of the first transconductance element and a second connection of the third negative feedback element is coupled to the positive output of the second transconductance element;

the second feedback element includes a fourth negative feedback element, wherein a first connection of the fourth negative feedback element is coupled to the negative output of the first transconductance element and a second connection of the fourth negative feedback element is coupled to the negative output of the second transconductance element;

the third feedback element includes a fifth negative feedback element, wherein a first connection of the fifth negative feedback element is coupled to the negative input of the second transconductance element and a second connection of the fifth negative feedback element is coupled to the positive output of the second transconductance element; and

the third feedback element includes a sixth negative feedback element, wherein a first connection of the sixth negative feedback element is coupled to the positive input of the second transconductance element and a second connection of the sixth negative feedback element is coupled to the negative output of the second transconductance element.

17. The method of claim 15 , wherein at least one of the first, second, or third feedback elements includes a resistor.

18. The method of claim 15 , wherein at least one of the first, second, or third feedback elements includes a capacitor.

19. The method of claim 15 , wherein at least one of the first, second, or third feedback elements includes an inductor.

20. The method of claim 15 , wherein the frequency f bp is higher in frequency than f i .