Double balanced mixer

1. An improved double balanced mixer, comprising:

a first balun for receiving a first single input and providing a first balanced output having two ports;

a second balun for receiving a second single input and providing a second balanced output having two ports;

a balanced mixer core responsive to said first and second balanced outputs to provide a mixed signal from said first and second single inputs; and

the first balun including a first RC network coupled between both of the ports of the first balanced output and one of ground and a common mode node of the first balun to improve the linearity of the double balanced mixer.

2. The improved double balanced mixer of claim 1 in which said second balun includes a second RC network coupled between at least one of the ports of the second balanced output and one of ground and a common mode node of the second balun.

3. The improved double balanced mixer of claim 1 in which the first balun includes a Marchand balun.

4. The improved double balanced mixer of claim 1 in which the first balun includes a back-wave balun.

5. The improved double balanced mixer of claim 1 in which the first balun includes a hybrid Marchand/back-wave balun.

6. The improved double balanced mixer of claim 5 in which each of said baluns includes a hybrid Marchand/back-wave balun which includes:

a first pair of coupled sections having a first primary section and first secondary section;

a second pair of coupled sections having a second primary section and second secondary section;

a first reactance interconnecting said first and second primary sections and a second reactance interconnecting said first and second secondary sections;

one of said reactances being open at high frequency and shorted at low frequency, the other reactance being shorted at high frequency and open at low frequency for selectively providing low frequency Marchand/high frequency back-wave function and high frequency Marchand/low frequency back-wave function.

7. The improved double balanced mixer of claim 6 in which said first reactance is an inductive reactance, said second reactance is a capacitive reactance and said balun functions as a Marchand balun at low frequency and a back-wave balun at high frequency.

8. The improved double balanced mixer of claim 6 in which said first reactance is a capacitive reactance, said second reactance is an inductive reactance and said balun functions as a Marchand balun at high frequency and a back-wave balun at low frequency.

9. The improved double balanced mixer of claim 6 in which one of the first and second reactances is a capacitive reactance and the other is an inductive reactance and they are implemented by parasitic capacitance and parasitic inductance of the coupled sections, respectively.

10. The improved double balanced mixer of claim 1 further including an impedance transforming network interconnected between said balanced mixer core and said balanced outputs of each of said baluns.

11. An improved double balanced mixer, comprising:

a first balun for receiving a first single input and providing a first balanced output having two ports;

a balanced mixer core responsive to said first balanced output and a second balanced output to provide a mixed signal from said first and second balanced outputs; and

the first balun including a first RC network coupled between both of the ports of the first balanced output and one of ground and a common mode node of the first balun to improve the linearity of the double balanced mixer.

12. The improved double balanced mixer of claim 11 further including a second balun for receiving a second single input and providing the second balanced output having two ports, said second balun including a second RC network coupled between at least one of the ports of the second balanced output and one of ground and a common mode node of the second balun.

13. The improved double balanced mixer of claim 11 in which the first balun includes a Marchand balun.

14. The improved double balanced mixer of claim 11 in which the first balun includes a back-wave balun.

15. The improved double balanced mixer of claim 11 in which the first balun balun includes a hybrid Marchand/back-wave balun.

16. An improved double balanced mixer, comprising:

a first balun for receiving a first single input and providing a first balanced output having two ports;

a second balun for receiving a second single input and providing a second balanced output having two ports;

a balanced mixer core responsive to said first and second balanced outputs to provide a mixed signal from said first and second single inputs;

the first balun including a first RC network coupled between both of the ports of the first balanced output and one of ground and a common mode node of the first balun to improve the linearity of the double balanced mixer; and

said second balun including a second RC network coupled between at least one of the ports of the second balanced output and one of ground and a common mode node of the second balun.

17. The improved double balanced mixer of claim 16 in which the first RC network includes resistor and capacitor coupled in series to one of the ports of the first balanced output.

18. The improved double balanced mixer of claim 16 in which the first RC network includes a resistor coupled to a common node of two coupled capacitors, each of which is coupled to a port of the first balanced output.

19. The improved double balanced mixer of claim 16 in which the first RC network includes a resistor coupled to a common node of two coupled capacitors, each of which is coupled to a port of the first balanced output.