Fuse-trimmed tank circuit for an integrated voltage-controlled oscillator

• US 6,445,257 B1
• Filed: 10/04/2000
• Issued: 09/03/2002
• Est. Priority Date: 11/23/1999
• Status: Expired due to Term

• Current Assignee: Qorvo US, Inc. (Qorvo, Inc.)
• Original Assignee: Micro Linear Corporation (Qorvo, Inc.)
• Inventors: Cox, Robert, Luff, Gwilym
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US09/680,396
• Time in Patent Office: 699 Days
• Field of Search: 331/36.C, 331/116.R, 331/116.FE, 331/117.R, 331/117.FE, 331/117.D, 331/177.V, 331/179
• US Class Current: 331/117.00R
• CPC Class Codes: H03B 5/1215 the current source or degeneration circuit being in common to both transistors of the pair, e.g. a cross-coupled long-tailed pair
• CPC Class Codes: H03B 5/1231 the amplifier comprising one or more bipolar transistors
• CPC Class Codes: H03B 5/1243 the means comprising voltage variable capacitance diodes
• CPC Class Codes: H03B 5/1265 switched capacitors
• CPC Class Codes: H03J 2200/36 Circuit arrangements for, e.g. increasing the tuning range, linearizing the voltage-capacitance relationship, lowering noise, constant slope in different bands

Abstract

A fuse-trimmed tank circuit for an integrated voltage-controlled oscillator (VCO). The tank circuit includes an L-C portion; a cross-coupled pair of transistors, whose collectors are coupled to the L-C portion; a capacitor coupled across the emitters of the cross-coupled pair of transistors; and a pair of resistors, where each resistor is coupled between a corresponding one of the emitters and a ground node. This oscillator circuit provides improved performance over prior oscillator circuits. A technique for trimming the VCO is utilized to adjust its center frequency. Capacitance for the L-C portion of the tank circuit is provided by one or more varactor diodes. When the VCO is operational, the varactors are reverse biased and, thus, act as capacitive elements. One or more of the varactors has an associated fuse coupled in series with the corresponding varactor. To trim the center frequency of the VCO, the capacitance of the L-C portion is adjusted by selectively blowing the fuses. To blow a fuse, a dc voltage is applied to forward bias the corresponding varactor such that the resulting current is sufficiently high to blow the fused. In the preferred embodiment, the varactors are arranged in pairs, where each varactor of the contributes to the capacitance of one or the other sides of the tank circuit for maintaining its symmetry. The two fuses associated with each varactor of the pair are preferably blown together. Preferably, the VCO is integrated into an integrated circuit.

Claims

1. A tank circuit for a voltage-controlled oscillator wherein the tank circuit comprises:

a. an L-C portion having a first capacitor;

b. a pair of transistors whose control terminals are coupled to the L-C portion;

c. a second capacitor coupled across output terminals of the pair of transistors; and

d. a pair of resistors, wherein each resistor is coupled between a corresponding one of the output terminals of the pair of transistors and a ground node.

2. The tank circuit according to claim 1 wherein the pair of transistors are a cross-coupled pair of transistors.

3. The tank circuit according to claim 1 wherein a periodic signal is formed across the second capacitor.

4. The tank circuit according to claim 3 wherein the periodic signal is substantially sinusoidal.

5. The tank circuit according to claim 1 wherein the L-C portion comprises a pair of inductors wherein the first capacitor is coupled to the pair of inductors.

6. The tank circuit according to claim 1 wherein a periodic signal is formed across the control terminals of the cross-coupled pair of transistors.

7. The tank circuit according to claim 6 wherein the periodic signal is substantially a sinusoid.

8. The tank circuit according to claim 1 further comprising a first varactor selectively coupled to the L-C portion for providing a variable capacitance value to the tank circuit.

9. The tank circuit according to claim 8 wherein the first varactor is selectively coupled to the L-C portion via a fuse.

10. The tank circuit according to claim 9 wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the first varactor.

11. The tank circuit according to claim 9 further comprising a second varactor coupled to the L-C portion wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the second varactor.

12. The tank circuit according to claim 1 further comprising a plurality of pairs of varactors removably coupled to the L-C portion for providing a variable capacitance value to the tank circuit.

13. The tank circuit according to claim 12 wherein each pair of varactors are removably coupled to the L-C portion via a corresponding pair of fuses.

14. The tank circuit according to claim 13 wherein each pair of varactors are removed by blowing both fuses of the corresponding pair of fuses.

15. The tank circuit according to claim 13 wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the plurality of pairs of varactors.

16. A tank circuit for a voltage-controlled oscillator wherein the tank circuit comprises:

a. an L-C portion having a first capacitor;

b. a cross-coupled pair of transistors whose control terminals are coupled to the L-C portion;

c. a second capacitor coupled across output terminals of the cross-coupled pair of transistors; and

d. a pair of resistors, wherein each resistor is coupled between a corresponding one of the output terminals of the cross-coupled pair of transistors and a ground node.

17. The tank circuit according to claim 16 wherein the cross-coupled pair of transistors includes a pair of cross-coupled bipolar transistors.

18. The tank circuit according to claim 17 wherein a periodic signal is formed across the second capacitor.

19. The tank circuit according to claim 18 wherein the periodic signal is substantially sinusoidal.

20. The tank circuit according to claim 17 wherein the L-C portion comprises a pair of inductors wherein the first capacitor is coupled to the pair of inductors.

21. The tank circuit according to claim 17 wherein a periodic signal is formed across the control terminals of the cross-coupled pair of transistors.

22. The tank circuit according to claim 21 wherein the periodic signal is substantially a sinusoid.

23. The tank circuit according to claim 17 further comprising a first varactor selectively coupled to the L-C portion for providing a variable capacitance value to the tank circuit.

24. The tank circuit according to claim 23 wherein the first varactor is selectively coupled to the L-C portion via a fuse.

25. The tank circuit according to claim 24 wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the first varactor.

26. The tank circuit according to claim 24 further comprising a second varactor coupled to the L-C portion wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the second varactor.

27. The tank circuit according to claim 17 further comprising a plurality of pairs of varactors removably coupled to the L-C portion for providing a variable capacitance value to the tank circuit.

28. The tank circuit according to claim 27 wherein each pair of varactors are removably coupled to the L-C portion via a corresponding pair of fuses.

29. The tank circuit according to claim 28 wherein each pair of varactors are removed by blowing both fuses of the corresponding pair of fuses.

30. The tank circuit according to claim 28 wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the plurality of pairs of varactors.

31. A tank circuit for a voltage-controlled oscillator wherein the tank circuit comprises:

1. an L-C portion; and

2. a first varactor removably coupled to the L-C portion for providing a variable capacitance value to the tank circuit,

wherein the first varactor is removably coupled to the L-C portion via a fuse.

32. The tank circuit according to claim 31 further comprising a second varactor coupled to the L-C portion wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the second varactor.

33. The tank circuit according to claim 31 wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the first varactor.

34. A tank circuit for a voltage-controlled oscillator wherein the tank circuit comprises:

1. an L-C portion; and

2. a plurality of pairs of varactors removably coupled to the L-C portion for providing a variable capacitance value to the tank circuit,

wherein each pair of varactors are removably coupled to the L-C portion via a corresponding pair of fuses.

35. The tank circuit according to claim 34 wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the plurality of pairs of varactors.

36. The tank circuit according to claim 34 wherein each pair of varactors are removed by blowing both fuses of the corresponding pair of fuses.

37. The tank circuit according to claim 36 further comprising a switch associated with the pair of fuses to be blown wherein a current through the switch blows each fuse of the pair.

38. A method of tuning a voltage-controlled oscillator wherein the method comprises steps of:

a. providing a capacitive element for a tank circuit wherein the capacitive element includes a varactor;

b. providing a fuse coupled in series with the varactor; and

c. adjusting a value of the capacitive element by selectively blowing the fuse.

39. A method of tuning a voltage-controlled oscillator wherein the method comprises steps of:

a. providing a capacitive element for a tank circuit wherein the capacitive element includes a first pair of varactors;

b. providing a fuse coupled in series with each varactor of the first pair of varactors; and

c. adjusting a value of the capacitive element by selectively blowing the fuses associated with the first pair of varactors.

40. The method according to claim 39 wherein the first pair of varactors have a common cathode.

41. The method according to claim 39 further comprising steps of:

a. providing a second pair of varactors included in the capacitive element;

b. providing a fuse coupled in series with each varactor of the additional pair;

and

c. adjusting a value of the capacitive element by selectively blowing the fuses associated with the additional pair of varactors.

42. The method according to claim 41 wherein the first and second pair of varactors have values selected according to a binary weighting scheme.

43. The method according to claim 41 wherein the first and second pair of varactors have different capacitive values and further comprising steps of:

a. measuring an oscillation frequency of the voltage-controlled oscillator; and

b. determining which of the first and second pairs of varactors should be blown during the step of adjusting by performing a calculation which takes into account the oscillation frequency measured during the step of measuring and which takes into account a desired oscillation frequency.

44. The method according to claim 43 wherein the steps of measuring and determining and performed iteratively.

45. A tank circuit for a voltage-controlled oscillator wherein the tank circuit comprises:

a. a first inductor having a first terminal and a second terminal;

b. a second inductor having a first terminal and a second terminal wherein a first terminal of the first inductor is coupled to a first terminal of the second inductor;

c. a first capacitor having a first terminal and a second terminal wherein the first terminal of the first capacitor is coupled to the second terminal of the first inductor;

d. a second capacitor having a first terminal and a second terminal wherein the first terminal of the second capacitor is coupled to the second terminal of the second inductor;

e. a first varactor having an anode and a cathode wherein the anode of the first varactor is coupled to the second terminal of the first inductor via a first fuse;

f. a second varactor having an anode and a cathode wherein the anode of the second varactor is coupled to the second terminal of the second inductor via a second fuse; and

g. a cross-coupled pair of transistors coupled to the second terminal of the first capacitor and to the second terminal of the second capacitor.

46. The tank circuit according to claim 45 wherein the first and second varactors comprise a first pair of varactors and the tank circuit further comprising one or more additional pairs of varactors for providing capacitance to the tank circuit.

47. The tank circuit according to claim 46 wherein an oscillation frequency of the tank circuit is controlled by applying a reverse bias voltage of variable magnitude to the pairs of varactors.

48. The tank circuit according to claim 46 wherein at least one pair of the additional pairs of varactors are coupled to the tank circuit via a corresponding pair of fuses.

49. The tank circuit according to claim 48 wherein selected pairs of varactors are removed by blowing both fuses of the corresponding pair of fuses.

50. The tank circuit according to claim 49 further comprising a switch associated with the pair of fuses to be blown wherein a current through the switch blows each fuse of the pair.