MULTI-TRANSFORMER ARCHITECTURE FOR AN ACTIVE RF CIRCUIT

• US 20080113643A1
• Filed: 11/09/2007
• Published: 05/15/2008
• Est. Priority Date: 11/15/2006
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: SiBEAM, Inc. (Lattice Semiconductor Corporation)
• Inventors: Emami-Neyestanak, Sohrab, Guan, Xiang, Doan, Chinh Huy
• Granted Patent: US 8,170,522 B2
• Time in Patent Office: Days
• US Class Current: 455/323
• CPC Class Codes: H01P 5/10 for coupling balanced lines or devices with unbalanced lines or devices
• CPC Class Codes: H03D 2200/0023 Balun circuits
• CPC Class Codes: H03D 7/1433 using bipolar transistors H03D7/145 takes precedence
• CPC Class Codes: H03D 7/1441 using field-effect transistors H03D7/145 takes precedence
• CPC Class Codes: H03D 7/1458 Double balanced arrangements, i.e. where both input signals are differential
• CPC Class Codes: H03H 7/09 Filters comprising mutual inductance
• CPC Class Codes: H03H 7/42 Networks for transforming balanced signals into unbalanced signals and vice versa, e.g. baluns
• CPC Class Codes: H04L 25/0266 Arrangements for providing Galvanic isolation, e.g. by means of magnetic or capacitive coupling
• CPC Class Codes: H04L 25/0274 Arrangements for ensuring balanced coupling
• CPC Class Codes: H04L 25/0276 Arrangements for coupling common mode signals

Abstract

A circuit features a balun having an unbalanced input and a balanced output, and a differential coupler having a symmetrical structure about a center axis. The differential coupler has a differential input and a differential output, the differential input being coupled to the balanced output of the balun. An impedance element is coupled to a circuit node of the differential coupler at a point along the center axis. Other embodiments are also described and claimed.

Claims

1. A circuit comprising:

a balun having an unbalanced input and a balanced output;

a differential coupler having a symmetrical structure about a center axis, the differential coupler having a differential input and a differential output, the differential input being coupled to the balanced output of the balun; and

an impedance element coupled to a circuit node of the differential coupler at a point along the center axis.

2. The circuit of claim 1 further comprising:

an active circuit having a differential input coupled to the differential output of the coupler, wherein impedance looking into the differential input of the active circuit has a negative resistance component over a frequency range of operation,

and wherein the impedance element has a positive resistance component that is greater than the absolute value of the negative resistance component somewhere in said frequency range of operation.

3. The circuit of claim 2 wherein the frequency range of operation is somewhere between 46 GHz and 52 GHz.

4. The circuit of claim 2 wherein the differential coupler comprises first and second transformers that are replicates and that are positioned on opposite sides of the center axis, said circuit node being common to the first and second transformers, wherein the impedance element couples said circuit node to AC ground for the circuit.

5. The circuit of claim 4 further comprising an impedance matching network coupled between the differential output of the differential coupler and the differential input of the active circuit.

6. The circuit of claim 4 further comprising an impedance matching network coupled between the differential output of the balun and the differential input of the differential coupler.

7. The circuit of claim 4 wherein the active circuit comprises a mixer, and the differential input of the active circuit is a local oscillator port of the mixer.

8. The circuit of claim 4 wherein the balun and the differential coupler are adapted to operate somewhere in the range 45 GHz-66 GHz.

9. The circuit of claim 1 further comprising:

a capacitor coupled in series with the impedance element to AC ground; and

a DC bias generator circuit coupled to a node that is common to the impedance element and the capacitor.

10. A circuit comprising:

a balun having a pair of transmission lines that make up its differential output;

a first coupled line pair one line of which has one end conductively coupled to one of the transmission lines of the balun;

a second coupled line pair one line of which has one end conductively coupled to the other one of the transmission lines of the balun;

the other line of the first pair has one end coupled to a virtual ground node and another end being one half of a differential output of the circuit;

the other line of the second pair has one end that is coupled to the virtual ground node and another end being the other half of the differential output of the circuit; and

an impedance element coupled to the virtual ground node.

11. The circuit of claim 10 wherein the impedance element is a lumped resistor.

12. The circuit of claim 10 wherein the impedance element couples the virtual ground node to ac ground somewhere in the range 10 GHz-100 GHz.

13. The circuit of claim 10 wherein the balun and the first and second coupled line pairs are adapted to operate somewhere in the range 45 GHz-66 GHz.

14. The circuit of claim 10 further comprising:

a capacitor coupled in series with the impedance element to AC ground; and

a DC bias generator circuit coupled to a node that is common to the impedance element and the capacitor.

15. A circuit comprising:

a first transformer having an unbalanced input and a balanced output; and

a second transformer having a balanced input coupled to the balanced output of the first transformer, the second transformer having a symmetrical structure about a center axis to provide its balanced input and a balanced output; and

a target circuit having a balanced input coupled to the balanced output of the second transformer.

16. The circuit of claim 15 further comprising:

an impedance element coupled to a circuit node of the second transformer at a point along the center axis, the impedance element having a resistive component that is greater than the absolute value of a negative resistive component of input impedance of the target circuit somewhere in a frequency range.

17. The circuit of claim 16 wherein the frequency range is 45 GHz-66 GHz.

18. The circuit of claim 15 further comprising:

a third transformer having a balanced input coupled to the balanced output of the second transformer, the third transformer having a symmetrical structure about a center axis to provide its balanced input and a balanced output.

19. The circuit of claim 18 further comprising:

an impedance element coupled to a circuit node of the third transformer at a point along its center axis, the impedance element having a resistive component that is greater than the absolute value of a negative resistive component of input impedance of the target circuit somewhere in a frequency range.

20. The circuit of claim 19 wherein the frequency range is somewhere between 45 GHz and 66 GHz.

21. An electronic system comprising:

a millimeter wave beam forming antenna array having

a mixer with an RF port coupled to an antenna array, and

a single-ended to differential transformer circuit having a balun with an unbalanced input and a balanced output adapted to operate somewhere in the range 45 GHz-66 GHz, a differential coupler with a symmetrical structure about a center axis and that contains first and second transformers which are replicates and that are positioned on opposite sides of the center axis, the differential coupler having a differential input and a differential output, the differential input being coupled to the balanced output of the balun, the differential output being coupled to an LO input of the mixer, and an impedance element coupled to a circuit node of the differential coupler that is common to the first and second transformers, wherein the impedance element couples said circuit node to ac ground.

22. The system of claim 21 wherein the mixer and single-ended to differential transformer circuit are integrated in a CMOS-processed chip.

23. The system of claim 22 in combination with a consumer product grade audio and/or video digital media receiver, wherein the mixer is an up-conversion device that receives an audio and/or video stream from the media receiver and transfers the stream to higher frequencies for transmission by the antenna array.

24. The system of claim 22 in combination with a consumer product grade audio and/or video digital media player, wherein the mixer is a down-conversion device that transfer an audio and/or video stream received by the antenna array to lower frequencies and sends the audio and/or video stream to the media player for playback.