Programmable filter for LC tank voltage controlled oscillator (VCO), design structure and method thereof

• US 8,373,510 B2
• Filed: 04/21/2008
• Issued: 02/12/2013
• Est. Priority Date: 04/21/2008
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Kelkar, Ram
• Primary Examiner(s): Kinkead, Arnold
• Assistant Examiner(s): Tan, Richard
• Application Number:
  US12/106,399
• Publication Number:
  US 20090261916A1
• Time in Patent Office: 1,758 Days
• Field of Search: 331/16, 331/17, 331/36.C, 331/44, 331/177.R, 331/177.V, 375/375, 375/376
• US Class Current: 331/16
• 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 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1265 switched capacitors

Abstract

A programmable filter for LC tank voltage controlled oscillator (VCO) and a design structure for a programmable filter for LC tank VCO. The programmable filter includes a proportional control comprising a plurality of capacitance biased by different input voltages and an integral control comprising a filter element with a capacitance C1 and a set of capacitance biased by a voltage output of the filter element.

Claims

1. A programmable filter, comprising:

a proportional control comprising a plurality of sets of variable capacitors connected to nodes VM1 and VP1 and biased by different input voltages, wherein the proportional control controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as a voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range; and

an integral control comprising a filter element with a capacitor C1 and a set of variable capacitors connected to the nodes VM1 and VP1 and biased by a voltage output of the filter element,

wherein one of the different input voltages is a variable voltage derived from the voltage output of the filter element.

10. The programmable filter of claim 1, wherein to decrease frequency, a bias voltage of capacitors C_C and C_D of the plurality of capacitors is switched from VCC to VCN.

2. A programmable filter, comprising:

a proportional control comprising a plurality of capacitors biased by different input voltages, wherein the proportional control controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as a voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range; and

an integral control comprising a filter element with a capacitor C1 and a set of capacitors biased by a voltage output of the filter element,

wherein switching between the different input voltages is controlled by phase detector outputs decrease (DEC) and increase inverse (INCN).

3. The programmable filter of claim 2, wherein:

a first input voltage of the different input voltages is a steady state input voltage (VCC) which is a constant bias voltage independent of voltage controlled oscillator (VCO) operating frequency; and

a second input voltage of the different input voltages is a variable voltage derived from the voltage output of the filter element (VCNTL1).

4. The programmable filter of claim 3, wherein the VCNTL1 is lower than the VCC.

5. The programmable filter of claim 3, wherein:

the VCC is a steady state voltage independent of oscillator frequency; and

the VCN is derived from the VCNTL1 and is lower than the VCC, such that a value of the plurality of capacitors increases when the DEC goes to logic 1 thereby reducing the VCO operating frequency.

6. A programmable filter, comprising:

a proportional control comprising a plurality of capacitors biased by different input voltages, wherein the proportional control controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as a voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range; and

an integral control comprising a filter element with a capacitor C1 and a set of capacitors biased by a voltage output of the filter element,

wherein the plurality of capacitors includes two sets of variable capacitors (C_C, C_D) and (C_E, C_F) controlled by phase detector outputs decrease (DEC) and increase inverse (INCN).

7. A programmable filter, comprising:

a proportional control comprising a plurality of capacitors biased by different input voltages, wherein the proportional control controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as a voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range; and

an integral control comprising a filter element with a capacitor C1 and a set of capacitors biased by a voltage output of the filter element,

wherein, in a normal state, capacitors C_C and C_D of the plurality of capacitors are biased to a steady state voltage (VCC) and capacitors C_E and C_F of the plurality of capacitors are biased to a voltage (VCN) derived from the voltage output of the filter element.

8. A programmable filter, comprising:

a proportional control comprising a plurality of capacitors biased by different input voltages VCC and VCN, wherein the proportional control controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as a voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range; and

an integral control comprising a filter element with a capacitor C1 and a set of capacitors biased by a voltage output of the filter element,

wherein, to increase frequency, a bias voltage of capacitors C_E and C_F of the plurality of capacitors is switched from VCN to VCC for as long as a phase detector output increase inverse (INCN) is low thereby reducing capacitance of the capacitors C_E and C_F since the VCC is higher than the VCN.

9. The programmable filter of claim 8, wherein when the INCN is high, the bias voltage of the capacitors C_E and C_F is biased to the VCN.

11. A programmable filter, comprising:

a proportional control comprising a plurality of capacitors biased by different input voltages, wherein the proportional control controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as a voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range; and

an integral control comprising a filter element with a capacitor C1 and a set of capacitors biased by a voltage output of the filter element,

wherein in a normal state a bias voltage of capacitors C_C and C_D of the plurality of capacitors is biased to VCN and a bias voltage of capacitors C_E and C_F is biased to VCC such that the capacitance of the capacitors C_C and C_D has increased and the capacitance of the capacitors C_E and C_F has decreased.

12. The programmable filter of claim 11, wherein a net change in capacitance of the capacitors C_C, C_D and C_E, C_F is 0.

13. A programmable filter, comprising:

a proportional control configured to have a capacitance biased between a variable voltage input derived from a voltage output of a filter element and a steady state voltage input independent of voltage controlled oscillator (VCO) frequency and controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as the VCO frequency changes over a VCO frequency range; and

an integral control configured to provide the voltage output of the filter element based on a single capacitance.

18. The programmable filter of claim 13, wherein to decrease frequency, a bias voltage of the capacitors C_C and C_D of the plurality of capacitors is switched from voltage VCC to VCN.

14. A programmable filter, comprising:

a proportional control configured to have a capacitance biased between a variable voltage input derived from a voltage output of a filter element and a steady state voltage input independent of voltage controlled oscillator (VCO) frequency and controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as the VCO frequency changes over a VCO frequency range; and

an integral control configured to provide the voltage output of the filter element based on a single capacitance,

wherein;

a bias of the proportional control is controlled by phase detector outputs decrease (DEC) and increase inverse (INCN); and

the steady state input voltage is independent of oscillator frequency.

15. A programmable filter, comprising:

a proportional control configured to have a capacitance biased between a variable voltage input derived from a voltage output of a filter element and a steady state voltage input independent of voltage controlled oscillator (VCO) frequency and controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as the VCO frequency changes over a VCO frequency range; and

an integral control configured to provide the voltage output of the filter element based on a single capacitance,

wherein the proportional control is implemented using two sets of variable capacitors (C_C, C_D) and (C_E, C_F) controlled by phase detector outputs decrease (DEC) and increase inverse (INCN).

16. A programmable filter, comprising:

a proportional control configured to have a capacitance biased between a variable voltage input derived from a voltage output of a filter element and a steady state voltage input independent of voltage controlled oscillator (VCO) frequency and controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as the VCO frequency changes over a VCO frequency range; and

an integral control configured to provide the voltage output of the filter element based on a single capacitance,

wherein, in a normal state, capacitors C_C and C_D of the proportional control are biased to a steady state voltage (VCC) and capacitors C_E and C_F of the proportional control are biased to a voltage (VCN) derived from the voltage output of the filter element.

17. A programmable filter, comprising:

a proportional control configured to have a capacitance biased between a variable voltage input (VCN) derived from a voltage output of a filter element and a steady state voltage input (VCC) independent of voltage controlled oscillator (VCO) frequency and controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as the VCO frequency changes over a VCO frequency range; and

an integral control configured to provide the voltage output of the filter element based on a single capacitance,

wherein;

to increase frequency a bias voltage of capacitors C_E and C_F of a plurality of capacitors is switched from the voltage VCN to the voltage VCC for as long as INCN is low thereby reducing capacitance of the capacitors C_E and C_F since the voltage VCC is higher than the voltage VCN, and

when the INCN is high, the bias voltage of the capacitors C_E and C_F is biased to the voltage VCN.

19. A programmable filter, comprising:

a proportional control configured to have a capacitance biased between a variable voltage input (VCN) derived from a voltage output of a filter element and a steady state voltage input (VCC) independent of voltage controlled oscillator (VCO) frequency and controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as the VCO frequency changes over a VCO frequency range; and

an integral control configured to provide the voltage output of the filter element based on a single capacitance,

wherein in a normal state a bias voltage of capacitors C_C and C_D of the plurality of capacitors is biased to the VCN and a bias voltage of capacitors C_E and C_F is biased to the VCC such that the capacitance of the capacitors C_C and C_D has increased and the capacitance of the capacitors C_E and C_F has decreased and a net change in capacitance of the capacitors C_C, C_D and C_E, C_F is 0.

20. A method comprising controlling capacitance value of a proportional control such that a frequency change due to the proportional control stays constant as voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range,

wherein the proportional control comprises a plurality of sets of variable capacitors connected to nodes VM1 and VP1 and biased by different input voltages;

an integral control comprises a filter element with a capacitor C1 and a set of variable capacitors connected to the nodes VM1 and VP1; and

one of the different input voltages is a variable voltage derived from a voltage output of the filter element.

21. A method comprising controlling capacitance value of a proportional control such that a frequency change due to a proportional control stays constant as voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range,

wherein at low values of a voltage output of a filter element (VCNTL1), a variable capacitor implementing the proportional control sees a larger change in capacitance value due to a larger bias voltage swing from a steady state voltage input (VCC) to a variable voltage input (VCN) and the proportional control value change will be lower for higher values of VCNTL1.

22. A design structure embodied in a machine readable medium comprising a memory for designing, manufacturing, or testing an integrated circuit, the design structure comprising:

a proportional control comprising a plurality of sets of variable capacitors connected to nodes VM1 and VP1 and biased by different input voltages, wherein the proportional control controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as a voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range; and

an integral control comprising a filter element with a capacitor C1 and a set of variable capacitors connected to the nodes VM1 and VP1 and biased by a voltage output of the filter element,

wherein one of the different input voltages is a variable voltage derived from the voltage output of the filter element.

23. The design structure of claim 22, wherein the design structure comprises a netlist.

24. The design structure of claim 22, wherein the design structure resides on the storage medium as a data format used for the exchange of layout data of integrated circuits.

25. The design structure of claim 22, wherein the design structure resides in a programmable gate array.

26. A programmable filter, comprising:

a proportional control comprising variable capacitors biased by different input voltages, wherein the proportional control controls a capacitance value change to ensure a frequency change due to the proportional control remains constant as a voltage controlled oscillator (VCO) operating frequency changes over a VCO frequency range; and

an integral control comprising a filter element with a capacitor and a set of variable capacitors biased by a voltage output of the filter element,

wherein one of the different input voltages is a variable voltage derived from the voltage output of the filter element.