Wideband differential amplifier including single-ended amplifiers coupled to a four-port transformer

1. A differential amplifier, comprising:

a first single-ended amplifier circuit;

a second single-ended amplifier circuit; and

a four-port transformer circuit having two input ports and two output ports, the two input ports being coupled to the first and second single-ended amplifier circuits, respectively, to form the differential amplifier, and the four-port transformer circuit operable to provide high common mode rejection of signals provided on the output ports.

2. The differential amplifier of claim 1 wherein the four-port transformer circuit provides common mode rejection that is sufficient to suppress even order intermodulation distortion signals on signals provided on the output ports.

3. The differential amplifier of claim 1 wherein the common mode rejection provides a common mode rejection ratio of greater than approximately ten decibels over a bandwidth from 6 GHz to 18 GHz.

4. The differential amplifier of claim 1 wherein the common mode rejection provides a common mode rejection ratio of greater than zero decibels over a desired bandwidth of the differential amplifier.

5. The differential amplifier of claim 4 wherein the desired bandwidth of the differential amplifier corresponds to signals having frequencies in the microwave frequency range.

6. The differential amplifier of claim 4 wherein the desired bandwidth of the differential amplifier corresponds to signals having frequencies less than the microwave frequency range.

7. The differential amplifier of claim 1 ,

wherein the transformer includes first and second input ports and third and fourth output ports;

wherein each of the single-ended amplifier circuits includes an input port and an output port;

wherein the output port of the first single-ended amplifier circuit is coupled to the first input port of the transformer; and

wherein the output port of the second single-ended amplifier circuit is coupled to the second input port of the transformer.

8. The differential amplifier of claim 1 ,

wherein the transformer includes first and second input ports and third and fourth output ports;

wherein each of the single-ended amplifier circuits includes an input port and an output port;

wherein the third output port of the transformer is coupled to the input port of the first single-ended amplifier circuit; and

wherein the fourth output port of the transformer is coupled to the input port of the second single-ended amplifier circuit.

9. The differential amplifier of claim 1 wherein each of the single-ended amplifier circuits has a distributed amplifier topology.

10. The differential amplifier of claim 1 wherein each of the single-ended amplifier circuits has a reactive match topology.

11. The differential amplifier of claim 1 wherein each of the single-ended amplifier circuits has a feedback topology.

12. The differential amplifier of claim 1 wherein each of the single-ended amplifier circuits has a lossy match topology.

13. The differential amplifier of claim 1 wherein each of the single-ended amplifier circuits has a 90 degree balanced topology.

14. The differential amplifier of claim 1 wherein the four-port transformer comprises a center tapped transformer.

15. The differential amplifier of claim 1 wherein the four-port transformer includes single coupled lines.

16. The differential amplifier of claim 1 wherein the four-port transformer comprises a compensated transformer.

17. A differential amplifier, comprising:

a first single-ended amplifier circuit;

a second single-ended amplifier circuit;

a four-port transformer circuit coupled to the first and second single-ended amplifier circuits to form the differential amplifier, the four-port transformer circuit operable to provide high common mode rejection over a bandwidth of the transformer circuit; and

wherein the first single-ended amplifier circuit and second single-ended amplifier circuit comprise a first stage of the amplifier, and wherein the amplifier further comprises additional stages coupled in series with the first stage, with four-port transformer circuits being connected between stages.

18. The differential amplifier of claim 17 wherein the amplifier includes one or more additional stages.

19. The differential amplifier of claim 17 wherein the four-port transformer circuit provides common mode rejection that is sufficient to suppress even order intermodulation distortion on signals provided on output ports of the four-port transformer circuit.

20. An electronic system, comprising:

electronic circuitry coupled to input, output, and storage devices, the electronic circuitry including a differential amplifier, the differential amplifier including,

a first single-ended amplifier circuit;

a second single-ended amplifier circuit;

a four-port transformer circuit coupled to the first and second single-ended amplifier circuits to form the differential amplifier, the four-port transformer circuit operable to have high common mode rejection and to suppress even order intermodulation distortion.

21. The electronic system of claim 20 wherein the electronic circuitry comprises cellular telephone circuitry.

22. The electronic system of claim 20 wherein the electronic circuitry comprises digital circuitry and wherein the differential amplifier functions to amplify complementary digital signals as part of input or output buffering circuitry or clock distribution circuitry.

23. A method of differentially amplifying input signals, the method comprising:

applying differential input signals to a four-port transformer;

rejecting common mode components of the differential input signals to thereby suppress intermodulation distortion signals on differential output signals; and

amplifying the differential output signals from the transformer.

24. The method of claim 23 wherein rejecting common mode components of the differential input signals comprises suppressing even order intermodulation distortion signals on the differential output signals.

25. The method of claim 23 wherein the frequency of operation is lower or higher than the microwave region.