System and method for a switchable capacitance

• US 9,584,097 B2
• Filed: 04/29/2014
• Issued: 02/28/2017
• Est. Priority Date: 04/29/2014
• Status: Active Grant

• Current Assignee: Infineon Technologies AG
• Original Assignee: Infineon Technologies AG
• Inventors: Bakalski, Winfried
• Primary Examiner(s): Takaoka, Dean
• Assistant Examiner(s): Wong, Alan
• Application Number:
  US14/264,937
• Publication Number:
  US 20150311883A1
• Time in Patent Office: 1,036 Days
• Field of Search: 333/24.C, 333/17.1, 333/17.3, 333/24.R, 333/172, 333/174, 327/337, 327/554
• US Class Current: 1/1
• CPC Class Codes: H03H 11/28 Impedance matching networks
• CPC Class Codes: H03J 2200/10 Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03J 5/244 using electronic means
• CPC Class Codes: H03K 17/687 the devices being field-effect transistors

Abstract

In accordance with an embodiment, a switchable capacitance circuit includes a plurality of capacitance-switch cells that each have a capacitance circuit having a capacitance between a first terminal and a second terminal of the capacitance circuit, and a semiconductor switching circuit including a first terminal coupled to the first terminal of the capacitance circuit, a plurality of series connected radio-frequency (RF) switch cells having a load path and a common node. Each of the plurality of series connected RF switch cells has a switch transistor and a gate resistor having a first end coupled to a gate of the switch transistor and a second end coupled to the common node. The switchable capacitance circuit also includes a resistance circuit having a first end coupled to the common node and a second end coupled to a control node.

Claims

1. A switchable capacitance circuit comprising:

a plurality of capacitance-switch cells, wherein each capacitance-switch cell comprises;

a capacitance circuit having a capacitance between a first terminal and a second terminal of the capacitance circuit; and

a semiconductor switching circuit comprising

a first terminal coupled to the first terminal of the capacitance circuit,

a plurality of series connected radio-frequency (RF) switch cells comprising a load path and a common node, wherein each of the plurality of series connected RF switch cells comprises a switch transistor and a gate resistor having a first end coupled to a gate of the switch transistor and a second end coupled to the common node, and

a resistance circuit having a first end coupled to the common node and a second end coupled to a control node, wherein the resistance circuit comprises a resistance between the first end and the second end,

wherein the gate resistor in each of the plurality of RF switch cells has a same resistance value,

wherein the switch transistors in a first of the plurality of capacitance-switch cells has a first width, the switch transistors in a second of the plurality of capacitance-switch cells has a second width, and the first width is different from the second width, and

wherein the resistance circuit in the first of the plurality of capacitance-switch cells is configured to set a switching time of the first of the plurality of capacitance-switch cells to substantially match a switching time of the second of the plurality of capacitance-switch cells, the resistance of the resistance circuit for first of the plurality of capacitance-switch cells being different from the resistance of the resistance circuit for the second of the plurality of capacitance-switch cells.

2. The switchable capacitance circuit of claim 1, wherein the second terminal of each capacitance circuit of the plurality of capacitance-switch cells are coupled to a same node.

3. The switchable capacitance circuit of claim 1, wherein a value of the resistance of the resistance circuit is inversely proportional to a value of the capacitance of the capacitance circuit of the plurality of capacitance-switch cells.

4. The switchable capacitance circuit of claim 1, wherein a value of the capacitance of the capacitance circuit of a first of the plurality of capacitance-switch cells is different from a value of the capacitance of a second of the plurality of capacitance-switch cells.

5. The switchable capacitance circuit of claim 4, wherein a value of the resistance of the resistance circuit is inversely proportional to the value of the capacitance of the capacitance circuit in the plurality of capacitance-switch cells.

6. The switchable capacitance circuit of claim 1, wherein:

the resistance circuit comprises a resistor coupled between the first end and the second end of the resistance circuit; and

the capacitance circuit comprises a capacitor coupled between the first terminal and the second terminal of the capacitance circuit.

7. The switchable capacitance circuit of claim 6, wherein the capacitor comprises a plurality of series connected capacitors.

8. The switchable capacitance circuit of claim 6, wherein:

the resistor comprises a value that is substantially equal to a value of the resistance between the first end and the second end of the resistance circuit; and

the capacitor comprises a value that is substantially equal to a value of the capacitance between the first terminal and the second terminal of the capacitance circuit.

9. The switchable capacitance circuit of claim 1, wherein values of the capacitance of the capacitance circuit of the plurality of capacitance-switch cells are binary weighted.

10. The switchable capacitance circuit of claim 1, further comprising a control circuit having a plurality of outputs coupled to the corresponding control nodes of the plurality of capacitance-switch cells.

11. The switchable capacitance circuit of claim 1, wherein a second terminal of the semiconductor switching circuit of each of the plurality of capacitance-switch cells is coupled to ground.

12. The switchable capacitance circuit of claim 1, wherein the first width of the switch transistors in the first of the plurality of capacitance-switch cells is proportional to the second width of the switch transistors in the second of the plurality of capacitance-switch cells.

13. A method of operating a switchable capacitance circuit, the method comprising:

increasing a load capacitance of the switchable capacitance circuit comprising switching-on at least one of a plurality of capacitance-switch cells, wherein

each of the plurality of capacitance-switch cells comprises

a capacitance circuit having a capacitance between a first terminal and a second terminal of the capacitance circuit, and

a semiconductor switching circuit comprising

a first terminal coupled to the first terminal of the capacitance circuit,

a plurality of series connected radio-frequency (RF) switch cells comprising a load path and a common node, wherein each of the plurality of series connected RF switch cells comprises a switch transistor and a gate resistor having a first end coupled to a gate of the switch transistor and a second end coupled to the common node, and

a resistance circuit having a first end coupled to the common node and a second end coupled to a control node, wherein the resistance circuit comprises a resistance between the first end and the second end,

wherein the gate resistor in each of the plurality of RF switch cells has a same resistance value,

wherein the switch transistors in a first of the plurality of capacitance-switch cells has a first width, the switch transistors in a second of the plurality of capacitance-switch cells has a second width, and the first width is different from the second width, and

wherein the resistance circuit in the first of the plurality of capacitance-switch cells is configured to set a switching time of a first of the plurality of capacitance-switch cells to substantially match a switching time of a second of the plurality of capacitance-switch cells, the resistance of the resistance circuit for first of the plurality of capacitance-switch cells being different from the resistance of the resistance circuit for the second of the plurality of capacitance-switch cells,

switching-on comprises activating the semiconductor switching circuit of the at least one of the plurality of capacitance-switch cells; and

decreasing the load capacitance of the switchable capacitance circuit comprising switching-off the at least of the plurality of capacitance-switch cells, wherein switching-off comprises deactivating the semiconductor switching circuit of the at least one of the plurality of capacitance-switch cells.

14. The method of claim 13, wherein activating the semiconductor switching circuit of the at least one of the plurality of capacitance-switch cells comprises activating the plurality of series connected RF switch cells of the at least one of the plurality of capacitance-switch cells via the control node.

15. The method of claim 13, wherein a value of the resistance of the resistance circuit is inversely proportional to a value of the capacitance of the capacitance circuit of the plurality of capacitance-switch cells.

16. The method of claim 13, further comprising applying a RF signal to the switchable capacitance circuit.

17. The method of claim 13, further comprising:

coupling the switchable capacitance circuit to an antenna; and

tuning the antenna by increasing and decreasing the load capacitance of the switchable capacitance circuit.

18. The method of claim 13, further comprising:

receiving a command from a digital interface; and

decoding the command, wherein increasing and decreasing the load capacitance further comprising selectively activating the semiconductor switching circuit of the plurality of capacitance-switch cells according to the decoded command.

19. A tunable radio-frequency (RF) circuit comprising:

a semiconductor substrate; and

a plurality of capacitance-switch cells disposed on the semiconductor substrate, wherein each capacitance-switch cell comprises;

a capacitor coupled between a first terminal and a second terminal, and

a semiconductor switching circuit comprising

a first terminal coupled to the first terminal of the capacitor,

a plurality of series connected radio-frequency (RF) switch cells comprising a load path and a common node, wherein each of the plurality of series connected RF switch cells comprises a switch transistor and a gate resistor having a first end coupled to a gate of the switch transistor and a second end coupled to the common node, and

a common resistor having a first end coupled to the common node and a second end coupled to a control node,

wherein the gate resistor in each of the plurality of RF switch cells has a same resistance value,

wherein the switch transistors in a first of the plurality of capacitance-switch cells has a first width, the switch transistors in a second of the plurality of capacitance-switch cells has a second width, and the first width is different than the second width, and

wherein the common resistor in the first of the plurality of capacitance-switch cells is selected such that a switching time of a first of the plurality of capacitance-switch cells substantially matches a switching time of a second of the plurality of capacitance-switch cells, the resistance of the resistance circuit for first of the plurality of capacitance-switch cells being different from the resistance of the resistance circuit for the second of the plurality of capacitance-switch cells.

20. The tunable RF circuit of claim 19, wherein a capacitance of the capacitor is inversely proportional to a resistance of the common resistor.

21. The tunable RF circuit of claim 19, wherein values of the capacitors of the plurality of capacitance-switch cells are binary weighted.

22. The tunable RF circuit of claim 19, wherein the switch transistor comprises a MOSFET transistor.

23. The tunable RF circuit of claim 22, wherein a gate width of the MOSFET transistor is proportional to a capacitance of the capacitor.

24. The tunable RF circuit of claim 19, wherein the capacitor comprises a metal-insulator-metal (MIM) capacitor.

25. The tunable RF circuit of claim 19, further comprising a driver circuit coupled to the control nodes of the plurality of capacitance-switch cells.

26. The tunable RF circuit of claim 25, further comprising at least one of a charge pump and a voltage regulator coupled to the driver circuit.