System and method for narrow band PLL tuning

• US 6,426,680 B1
• Filed: 05/26/2000
• Issued: 07/30/2002
• Est. Priority Date: 05/26/1999
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Broadcom Corporation (Broadcom, Inc.)
• Inventors: Duncan, Ralph, Kwan, Tom W.
• Primary Examiner(s): MIS, DAVID C
• Application Number:
  US09/580,014
• Time in Patent Office: 795 Days
• Field of Search: 331/11, 331/14, 331/16, 331/25, 331/34, 331/36.C, 331/117.R, 331/117.FE, 331/176, 331/177.V, 331/179, 331/17
• US Class Current: 331/34
• CPC Class Codes: H01F 17/0006 Printed inductances printed coils for dynamo-electric machines H02K3/26; printed circuits H05K
• CPC Class Codes: H01F 17/0013 with stacked layers
• CPC Class Codes: H01F 2017/0053 with means to reduce eddy currents
• CPC Class Codes: H01F 2021/125 Printed variable inductor with taps, e.g. for VCO
• CPC Class Codes: H01L 23/5227 Inductive arrangements or effects of, or between, wiring layers other inductive arrangements H01L23/645
• CPC Class Codes: H01L 27/0248 for electrical or thermal protection, e.g. electrostatic discharge [ESD] protection
• CPC Class Codes: H01L 27/08 including only semiconductor components of a single kind
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 2924/3011 Impedance
• CPC Class Codes: H03B 2200/0038 including a current mirror
• CPC Class Codes: H03B 2201/025 the means being an electronic switch for switching in or out oscillator elements
• CPC Class Codes: H03B 2201/0266 the means comprising a transistor
• CPC Class Codes: H03B 5/1209 the amplifier having two current paths operating in a differential manner and a current source or degeneration circuit in common to both paths, e.g. a long-tailed pair. H03B5/1215 takes precedence
• CPC Class Codes: H03B 5/1212 the amplifier comprising a pair of transistors, wherein an output terminal of each being connected to an input terminal of the other, e.g. a cross coupled pair
• CPC Class Codes: H03B 5/1228 the amplifier comprising one or more field effect transistors
• CPC Class Codes: H03B 5/1253 the transistors being field-effect transistors
• CPC Class Codes: H03B 5/364 the amplifier comprising field effect transistors H03B5/366 takes precedence
• CPC Class Codes: H03D 7/161 all the frequency changers being connected in cascade
• CPC Class Codes: H03D 7/18 : Modifications of frequency-changers for eliminating image frequencies H03D7/16 takes precedence
• CPC Class Codes: H03G 1/0029 : using FETs
• CPC Class Codes: H03H 11/1291 : Current or voltage controlled filters
• CPC Class Codes: H03J 1/0075 : where the receiving frequencies of the stations are stored in a permanent memory, e.g. ROM
• CPC Class Codes: H03J 2200/10 : Tuning of a resonator by means of digitally controlled capacitor bank
• CPC Class Codes: H03J 3/04 : Arrangements for compensating for variations of physical values, e.g. temperature
• CPC Class Codes: H03J 3/08 : by varying a second parameter simultaneously with the tuning, e.g. coupling bandpass filter
• CPC Class Codes: H03J 3/185 : with varactors, i.e. voltage variable reactive diodes
• CPC Class Codes: H03L 1/023 : by using voltage variable capacitance diodes
• CPC Class Codes: H03L 7/10 : for assuring initial synchronisation or for broadening the capture range
• CPC Class Codes: H03L 7/23 : with pulse counters or frequency dividers

Abstract

An integrated VCO having an improved tuning range over process and temperature variations. There is therefore provided in a present embodiment of the invention an integrated VCO. The VCO comprises, a substrate, a VCO tuning control circuit responsive to a VCO state variable that is disposed upon the substrate, and a VCO disposed upon the substrate, having a tuning control voltage input falling within a VCO tuning range for adjusting a VCO frequency output, and having its tuning range adjusted by the tuning control circuit in response to the VCO state variable.

Claims

1. An integrated VCO comprising:

a substrate;

a VCO tuning control circuit responsive to a VCO state variable that is disposed upon the substrate; and

a VCO disposed upon the substrate, having a tuning control voltage input falling within a VCO tuning range for adjusting a VCO frequency output, and having the VCO tuning range adjusted by the tuning control circuit in response to the VCO state variable

wherein the VCO tuning control circuit includes

a window detector comparing a signal derived from a PLL loop filter output to a fixed voltage difference between an upper and a lower threshold that define a window,

a compensation circuit coupled to the window detector that simultaneously adjusts the upper and lower thresholds in response to temperature and process variations while maintaining the fixed voltage difference, and

a tuning register coupled to the output of the window detector generating a VCO tuning range adjustment signal.

2. The integrated VCO of claim 1, wherein the VCO is a negative g_m LC oscillator.

3. The integrated VCO of claim 1, wherein the VCO includes NMOS transistors configured to provide a capacitance that varies in response to an applied control voltage.

4. The integrated VCO of claim 1, wherein the VCO includes an adaptive bias circuit.

5. The integrated VCO of claim 4, in which the adaptive bias circuit includes a PMOS transistor having its source to drain coupled in series with a power supply line.

6. The integrated VCO of claim 1, additionally including an adjustable capacitance responsive to the tuning control voltage.

7. The integrated VCO of claim 6, in which the adjustable capacitance includes:

a first NMOS transistor configured as a varactor with its gate coupled to a second terminal of a first inductor and with its source and drain coupled to the tuning control voltage; and

a second NMOS transistor configured as a varactor with its gate coupled to a second terminal of a second inductor and with its source and drain coupled to the tuning control voltage.

8. The integrated VCO of claim 6, in which the adjustable capacitance includes:

a first field effect transistor with its gate coupled to a second terminal of a first inductor and with its source and drain coupled to the tuning control voltage;

a second field effect transistor with its gate coupled to the second terminal of a second inductor and with its source and drain coupled to the tuning control voltage; and

whereby the tuning control voltage is applied at a virtual ground such that the adjustable capacitance formed is an adjustable capacitance in parallel with a series of switched capacitors.

9. The integrated VCO of claim 6, in which the adjustable capacitance includes a series of switched capacitors having:

a transistor switch; and

a capacitance in series with the transistor switch.

10. The integrated VCO of claim 9, wherein the capacitance in series with the transistor switch comprises a metal fringe capacitor.

11. The integrated VCO of claim 1, wherein the VCO state variable is the tuning control voltage.

12. The integrated VCO of claim 1, wherein the VCO further includes a feedback network having a resonant frequency that varies with the tuning control voltage input and a set of control signals that act on the feedback network to change the VCO tuning range.

13. The integrated VCO of claim 1, wherein the feedback network further includes a bank of switched capacitors acted upon by the set of control signals to change the VCO tuning range.

14. The integrated VCO of claim 11, wherein the compensation circuit includes a FET connected to said window comparator, the FET having a gate voltage that varies with temperature, the gate voltage determining the upper and lower thresholds that determine the window of the window detector.

15. The integrated VCO of claim 14, wherein the gate voltage of the FET also varies with process.

16. The integrated VCO of claim 14, wherein the FET is a MOSFET.

17. An integrated VCO comprising:

a substrate;

a VCO disposed upon the substrate, having an adjustable frequency output responsive to a control voltage that is variable within an adjustable tuning range; and

a VCO tuning control circuit responsive to temperature and process variations and a tuning control voltage input falling within a fixed VCO tuning window, the window having a first threshold voltage in fixed relation to a second threshold voltage the first and second threshold voltages being adjusted in fixed relation to each other to modify an adjustable tuning range of the VCO.

18. A method of controlling stability of frequency output of a voltage controlled oscillator (VCO) over temperature and process variations, the VCO having a tank circuit with a tank circuit resonant frequency, the tank circuit including switched capacitors and varactors, the varactors being responsive to a varactor bias frequency output control voltage, the method comprising:

providing a temperature and process dependent moving voltage window, the temperature and process dependent moving voltage window defining upper and lower limits of a VCO voltage control range and maintaining a constant differential voltage between the upper and lower limits;

deriving VCO control voltages from the temperature and process dependent moving voltage window; and

applying the VCO control voltages to the switched capacitors to set a frequency tuning range for the tank circuit.

19. The method of claim 18, wherein the varactor bias frequency output control voltage adjusts frequency within the frequency tuning range set by the VCO control voltages.

20. The method of claim 18, wherein the temperature and process dependent moving voltage window is established by comparing a voltage derived from the varactor bias frequency output control voltage with temperature and process dependent reference voltages.

21. The method of claim 18, wherein the VCO forms part of a phase locked loop (PLL) and the applying the VCO control voltages to the switched capacitors to adjust the tank circuit resonant frequency is used to improve frequency lock for the PLL over the temperature and process variations.

22. A tuning process for establishing a range of VCO control voltages that establish a PLL lock condition comprising:

evaluating a state variable derived from a PLL loop filter;

comparing the state variable to a predefined sliding window comprising a fixed difference between an upper and a lower limit, in which the upper and lower limits change in response to temperature and process variations, while maintaining the fixed relationship between upper and lower limits;

shifting zeroes through a shift register if the state variable exceeds the upper limit of the predefined sliding window to decrease a VCO tank capacitance;

shifting ones through the shift register if the state variable is less than the lower limit of the predefined sliding window to increase the VCO tank capacitance;

disabling the shift register if the state variable falls within the predefined sliding window while continuing to monitor the state variable;

initiating a timer when the state variable falls within the predefined sliding window;

timing the time the state variable remains within the predefined window;

comparing the time the state variable remains within the predefined window to a predefined time limit;

producing an inlock flag if the state variable remains within the predefined window for a predefined time; and

disabling a control circuit upon completion of the tuning process.

23. An integrated VCO comprising:

a substrate means for supporting the disposition of an integrated circuit;

a VCO means for producing a range of frequencies in response to a changing voltage input; and

a VCO control circuit means for changing the range of frequencies produced in response to the changing voltage input through the use of a temperature and process dependent sliding window.

24. The integrated VCO of claim 23, wherein the VCO control circuit means includes:

a window detector comparing a signal derived from a PLL loop filter output to a fixed voltage difference between an upper and a lower threshold that define a window;

a compensation circuit coupled to the window detector that simultaneously adjusts the upper and lower thresholds in response to temperature and process variations while maintaining the fixed voltage difference; and

a tuning register coupled to the output of the window detector generating a VCO tuning range adjustment signal.

25. The integrated VCO of claim 24, wherein the compensation circuit includes a FET connected to the window comparator, the FET having a gate voltage that varies with temperature, the gate voltage determining the upper and lower thresholds that determine the window of the window detector.

26. An integrated VCO comprising:

a substrate;

a VCO tuning control circuit responsive to a VCO state variable that is disposed upon the substrate;

a VCO disposed upon the substrate, having a tuning control voltage input falling within a VCO tuning range for adjusting a VCO frequency output, and having the VCO tuning range adjusted by the tuning control circuit in response to the VCO state variable; and

an adaptive bias circuit having a PMOS transistor with its source to drain coupled in series between a power supply line and the VCO.

27. An integrated VCO comprising:

a substrate;

a VCO tuning control circuit responsive to a VCO state variable that is disposed upon the substrate;

a VCO disposed upon the substrate, having a tuning control voltage input falling within a VCO tuning range for adjusting a VCO frequency output, and having the VCO tuning range adjusted by the tuning control circuit in response to the VCO state variable; and

an adjustable capacitance responsive to the tuning control voltage, including

a first NMOS transistor configured as a varactor with its gate coupled to a second terminal of a first inductor and with its source and drain coupled to the tuning control voltage, and

a second NMOS transistor configured as a varactor with its gate coupled to a second terminal of a second inductor and with its source and drain coupled to the tuning control voltage.

28. An integrated VCO comprising:

a substrate;

a VCO tuning control circuit responsive to a VCO state variable that is disposed upon the substrate;

a VCO disposed upon the substrate, having a tuning control voltage input falling within a VCO tuning range for adjusting a VCO frequency output, and having the VCO tuning range adjusted by the tuning control circuit in response to the VCO state variable;

an adjustable capacitance responsive to the tuning control voltage, including

a first field effect transistor with its gate coupled to a second terminal of a first inductor and with its source and drain coupled to the tuning control voltage, and

a second field effect transistor with its gate coupled to the second terminal of a second inductor and with its source and drain coupled to the tuning control voltage,

whereby the tuning control voltage is applied at a virtual ground such that the adjustable capacitance formed is an adjustable capacitance in parallel with a series of switched capacitors.