Clock signal from an adjustable oscillator for an integrated circuit

Claims

What is claimed is:

1. An integrated circuit comprising:

an adjustable oscillator circuit for producing a clock signal that controls multiple functions of the integrated circuit;

multiple sensors for detecting multiple dynamic parameters of the integrated circuit;

a lookup table containing data representing a fast operable clock frequency for each combination of the multiple dynamic parameters of the flash memory circuit; and

control circuitry for adjusting the adjustable oscillator circuit to produce the clock signal at the faste operable frequency based on the data loaded from the lookup table.

2. The integrated circuit of claim 1 further comprising:

an internal detection circuit for measuring a dynamic parameter or parameters and outputting a multiple bit output signal.

3. The integrated circuit of claim 2 wherein at least one of the dynamic parameters is a temperature of the integrated circuit.

4. The integrated circuit of claim 2 wherein at least one of the dynamic parameters is a supply voltage level of the integrated circuit.

5. The integrated circuit of claim 2 wherein the lookup table further comprises:

a data register containing data corresponding to possible states of the multiple bit output signal, the control circuitry adjusts the frequency of the clock signal based upon data retrieved from the data register.

6. The integrated circuit of claim 5 wherein the data in the data register is changed in response to a detected error in operation of the integrated circuit.

7. The integrated circuit of claim 1 wherein the adjustable oscillator circuit comprises:

a ring oscillator having a plurality of cascaded delay stages; and

controllable feedback circuitry for selectively coupling an output of one of the cascaded delay stages to an input of the ring oscillator.

8. The integrated circuit of claim 7 wherein the adjustable oscillator further comprises:

calibration circuitry for calibrating the ring oscillator to a nominal clock signal frequency.

9. The integrated circuit of claim 8 wherein the calibration circuitry comprises:

a counter coupled to the ring oscillator for counting transitions of the clock signal; and

a calibrate input coupled to the counter for receiving a calibrate pulse signal having a predetermined duration.

10. The integrated circuit of claim 7 wherein the adjustable oscillator further comprises:

de-couple circuitry connected to the ring oscillator for disabling unused ones of the plurality of cascaded delay stages.

11. The integrated circuit of claim 1 further comprising:

divider circuitry having divider stages coupled to the adjustable oscillator circuit for dividing the clock signal to produce an output signal having a frequency which is less than a frequency of the clock signal.

12. The integrated circuit of claim 11 wherein the divider circuitry further comprises:

disable circuitry for disabling unused ones of the divider stages.

13. The integrated circuit of claim 1 wherein the integrated circuit is a memory device.

14. The integrated circuit of claim 1 further including disable circuitry to disable part of the adjustable oscillator to reduce power consumption.

15. The integrated circuit of claim 1 wherein the control circuitry adjusts the frequency of the clock signal when an error is detected in operating the integrated circuit.

16. A flash memory device comprising:

an adjustable oscillator circuit for producing a clock signal that controls multiple functions of the flash memory device;

internal circuitry for measuring multiple dynamic parameters of the memory device; and

control circuitry for adjusting a frequency of the clock signal to a fast operable frequency in response to the measured dynamic parameters.

17. The flash memory device of claim 16 wherein the internal circuitry for measuring at least one of the dynamic parameters comprises a temperature detector for detecting a temperature of the flash memory.

18. The flash memory device of claim 17 wherein the temperature detector comprises:

a reference circuit for providing a plurality of reference voltages;

a temperature sensitive unit for producing a temperature sensitive voltage; and

a plurality of differential circuits coupled to the temperature sensitive unit and the reference circuit, each of the differential circuits comparing one of the plurality of reference voltages with the temperature sensitive voltage for providing an output on a plurality of output lines.

19. The flash memory device of claim 18 wherein the temperature sensitive unit comprises a diode connected between the plurality of differential circuits and ground potential.

20. The flash memory device of claim 19 wherein the diode is fabricated as a transistor having a connected gate and drain.

21. The flash memory device of claim 17 wherein the temperature detector provides a multiple-bit output signal.

22. The flash memory device of claim 16 wherein the internal circuitry for measuring the multiple dynamic parameters comprises a voltage detector for detecting a supply voltage level of the flash memory.

23. The flash memory device of claim 22 wherein the voltage detector comprises:

a voltage divider circuit coupled between the supply voltage and a lower voltage; and

a plurality of differential circuits coupled to the voltage divider circuit and a reference voltage, each of the differential circuits comparing a voltage sampled from the voltage divider circuit with the reference voltage for providing an output on a plurality of output nodes.

24. The flash memory device of claim 23 wherein the voltage detector further comprises:

reset circuitry for resetting the output on the output nodes to a predetermined level, and disabling the differential circuits.

25. The flash memory device of claim 24 wherein the reset circuitry further comprises:

pull-up transistors connected to the output nodes, the pull-up transistors being activated by a reset signal; and

disable circuitry connected to the plurality of differential circuits for disabling the plurality of differential circuits in response to the reset signal.

26. The flash memory device of claim 23 wherein the voltage detector provides a four bit output signal on the plurality of output nodes.

27. The flash memory device of claim 16 wherein the adjustable oscillator circuit comprises:

a ring oscillator having a plurality of cascaded delay stages: and

controllable feedback circuitry for selectively coupling an output of one of the cascaded delay stages to an input of the ring oscillator.

28. The flash memory device of claim 27 further comprising:

a multiplex circuit connected to the ring oscillator for selectively coupling one of the plurality of cascaded delay stages to an input of the ring oscillator in response to multiplex circuit input signals.

29. The flash memory device of claim 28 further comprising:

a small delay adjustment circuit located between the multiplex circuit and the input of the ring oscillator for further adjusting a frequency of the clock signal.

30. A flash memory device comprising:

an adjustable ring oscillator having a plurality of cascaded delay stages for producing a clock signal;

controllable feedback circuitry for selectively coupling an output of one of the cascaded delay stages to an input of the ring oscillator;

internal circuitry for measuring a dynamic parameter of the memory device;

control circuitry for adjusting a frequency of the clock signal in response to a measured dynamic parameter; and

a register circuit coupled to the ring oscillator to disable unused ones of the plurality of cascaded delay stages.

31. The flash memory device of claim 16 further comprising:

calibration circuitry for calibrating the adjustable oscillator circuit to a nominal clock signal frequency.

32. The flash memory device of claim 31 wherein the calibration circuitry comprises:

a counter coupled to the adjustable oscillator circuit for counting transitions of the clock signal and providing an output; and

a calibrate input coupled to the counter for receiving a calibrate pulse signal having a predetermined duration.

33. A flash memory device comprising:

an adjustable oscillator circuit for producing a clock signal;

internal circuitry for measuring a dynamic parameter of the memory device;

control circuitry for adjusting a frequency of the clock signal in response to a measured dynamic parameter;

calibration circuitry for calibrating the adjustable oscillator circuit to a nominal clock signal frequency;

a counter coupled to the adjustable oscillator circuit for counting transitions of the clock signal and providing an output;

a calibrate input coupled to the counter for receiving a calibrate pulse signal having a predetermined duration; and

a buffer coupled to the counter for gating an output count of the counter.

34. The flash memory device of claim 31 wherein the calibration circuitry further comprises:

an enable circuit coupled between the calibrate input and the counter for enabling the counter in response to either the calibrate pulse or a second input signal.

35. The flash memory device of claim 16 wherein the control circuitry adjusts the frequency of the clock signal to maintain a constant flash memory device operating speed.

36. The flash memory device of claim 16 wherein the control circuitry adjusts the frequency of the clock signal to optimize performance of the flash memory device.

37. The flash memory device of claim 16 further including disable circuitry to disable part of the adjustable oscillator to reduce power consumption.

38. The flash memory device of claim 16 wherein the control circuitry adjusts the frequency of the clock signal when an error is detected in operating the flash memory device.

39. A method of operating a memory circuit having an adjustable oscillator circuit for providing a clock signal, the method comprising:

calibrating the adjustable oscillator circuit to provide a clock signal that controls multiple functions and has a predetermined frequency;

detecting multiple dynamic parameters of the memory circuit; and

adjusting the adjustable oscillator in response to the detected dynamic parameters to change the frequency of the clock signal to a fast operable frequency.

40. The method of claim 39 wherein the oscillator comprises a cascaded series of delay stages, and the step of adjusting the oscillator comprises:

selectively coupling an output of one of the delay stages to an input of the oscillator through a feedback circuit.

41. The method of claim 40 further comprising disabling unused ones of the delay stages to save power consumption.

42. The method of claim 39 wherein detecting multiple dynamic parameters of the memory circuit further comprises detecting a temperature of the memory circuit.

43. The method of claim 42 wherein the step of detecting a temperature comprises:

providing a multiple bit output signal from a temperature detector circuit indicating a temperature range; and

providing a feedback control signal in response to the step of comparing for adjusting the adjustable oscillator.

44. The method of claim 43 further comprising comparing the multiple bit output signal with data stored in the memory circuit.

45. The method of claim 39 wherein detecting multiple dynamic parameters of the memory circuit further comprises detecting a supply voltage of the memory circuit.

46. The method of claim 45 wherein detecting a supply voltage comprises:

providing a multiple bit output signal from a supply voltage detector circuit indicating a supply voltage range; and

providing a feedback control signal in response to the step of comparing for adjusting the adjustable oscillator.

47. The method of claim 43 further comprising comparing the multiple bit output signal with data stored in the memory circuit.

48. The method of claim 39 wherein calibrating the adjustable oscillator circuit comprises:

counting transitions of the clock signal during a predetermined time period;

comparing the count of the transitions with data stored in the memory circuit; and

providing a feedback control signal in response to the step of comparing for adjusting the adjustable oscillator to provide the clock signal having a predetermined frequency.

49. A method of operating a memory circuit having an adjustable oscillator circuit for providing a clock signal, the method comprising;

calibrating the adjustable oscillator circuit to provide a clock signal having a predetermined frequency;

detecting a dynamic parameter of the memory circuit in response to a condition selected from the conditions comprising:

power is supplied to the memory;

the memory is placed in an idle state;

an error is detected in operation of the memory;

a predetermined number of program verify failures are detected in memory operation;

an erase failure is detected in memory operation;

a user command to check and adjust the dynamic parameter is received; and

a user command to load adjustment values is received; and

adjusting the adjustable oscillator in response to the detected dynamic parameter to change the frequency of the clock signal.

50. A method of operating a memory device comprising a clock circuit for providing a clock signal having a frequency, the memory device being designed to operate over an environmental parameter having lower, nominal, and upper levels, the method comprising the steps of:

adjusting the clock circuit so that the frequency of the clock signal is at a predetermined level when the environmental parameter is at the nominal level;

detecting a level of the environmental parameter;

adjusting the frequency of the clock signal based upon the detected level of the environmental parameter;

monitoring the operation of the memory device to detect operating errors;

resetting the clock circuit to the predetermined level if errors are detected;

detecting a new level of the environmental parameter after the clock circuit has been reset; and

adjusting the frequency of the clock signal based upon the detected new level of the environmental parameter.

51. A integrated circuit system comprising:

a plurality of integrated circuits, each of the integrated circuits comprising:

an adjustable oscillator circuit for producing a clock signal that controls multiple functions, and

an internal detection circuit for measuring a plurality of dynamic parameters and outputting an output signal; and

a controller coupled to the plurality of integrated circuits, the controller adapted to receive an output signal from the internal detection circuit of each of the plurality of integrated circuits, and provide a clock adjust signal to adjust a frequency of the clock signal of each of the adjustable oscillator circuits to a fast operable frequency in response to the output signals.

52. The integrated circuit system of claim 51 wherein the at least one of the plurality of dynamic parameters is temperature.

53. The integrated circuit system of claim 52 wherein the at least one of the plurality of dynamic parameters is a supply voltage level.

54. The integrated circuit system of claim 51 wherein the internal detection circuit measures both temperature and supply voltage.

55. The integrated circuit system of claim 51 wherein the controller calibrates the clock signal of the adjustable oscillator.

56. The integrated circuit system of claim 51 wherein the plurality of integrated circuits comprise flash memory devices.

57. The integrated circuit system of claim 51 wherein the controller comprises:

a data register containing data corresponding to possible states of the output signal, the controller providing the clock adjust signal based upon data retrieved from the data register.

58. A method of operating an integrated circuit, the method comprising the steps of:

monitoring environmental operating conditions;

reading a state of a data flag;

retrieving a clock setting corresponding to the monitored operating conditions from a first data table if the data flag is in a first state, and selecting a clock frequency so that the integrated circuit operated at its maximum performance under the monitored environmental operating conditions;

retrieving a clock oscillator setting corresponding to the monitored operating conditions from a second data table if the data flag is in a second state, and adjusting a clock oscillator so that the integrated circuit operates at a constant frequency under changes in the monitored environmental operating conditions.

59. A flash memory circuit comprising:

an adjustable oscillator circuit for producing a clock signal that controls multiple functions of the flash memory;

multiple sensors for detecting multiple dynamic parameters of the flash memory circuit;

a lookup table containing a delay offset factor for each combination of the multiple dynamic parameters of the flash memory circuit; and

control circuitry for adjusting the adjustable oscillator circuit to to produce the clock signal at the constant frequency based on the delay offset factor loaded from the lookup table.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to integrated circuits and in particular the present invention relates to dynamically controlling the operation of an integrated circuit.

BACKGROUND OF THE INVENTION

Almost all electronic systems rely on a clock source and clock signal to act as a master timing element for control of hardware included in the system. Several different methods of generating a clock signal are known to those skilled in the art. Three commonly used oscillators described below are based on either a crystal, a resistor-capacitor network, or a ring oscillator. None of these options provide a low cost, high accuracy clock signal.

Traditional methods of generating the clock signal have used crystals. While this method is well known and is very reliable, several problems are introduced when the electronic system package is reduced in size. Additional problems are encountered when reducing the cost and power consumption of the system become dominant considerations.

The frequency of a crystal operating point is determined by the physical characteristics of the crystalline structure. This physical dependance dictates the size of the package, preventing its use in some applications required to fit into very small packages, such as small memory cards. Further, crystal oscillators require valuable circuit board space and have minimum height restrictions. A system incorporating a crystal, therefore, is limited in the ability to reduce packaging sizes. A crystal-based system also requires extra pins for connecting the crystal to an integrated circuit requiring the clock signal. In addition, a typical crystal design requires a resistor and capacitor, adding cost, but more importantly taking more board space.

Crystal oscillator designs have additional disadvantages. The crystal oscillators do not operate over extended voltage ranges. Therefore, a supply voltage which ranges from three to five volts can create problems. Crystals also have long start times when power to the system is turned on. These start times must be taken into account so that glitches and low voltage signals do not make the system malfunction. During a start-up, the oscillator can be disconnected from the system until the crystal has reached a stabile operating point. The time required to stabilize the crystal can be quite long and will reduce the performance of systems that require extensive use of power on/off. One type of system affected is portable battery-driven circuits which turn off the power supply to conserve the battery. In addition to the power and performance problems described, crystals are somewhat expensive and further add to the cost of systems.

Crystal-based systems can be quite power demanding. If a crystal oscillator is used, it requires significant current for its operation, typically 1 mA per 1 megahertz of operation. For example, if a crystal is used across an inverter in an integrated circuit, the inverter must be of sufficient strength to allow oscillation and drive the loads required. This typically requires large current for proper operation. Because of the slow start-up time, the systems tend to leave power applied to the crystal. Again, continuously powering the crystal results in high power consumption, making the systems less attractive in battery applications.

One solution that designers have devised to reduce the slow start up time of crystals is to use of resistor-capacitor (RC) oscillator designs. RC oscillators do not have the frequency accuracy of crystal oscillator, but have other operational advantages. The use of an RC oscillator essentially allows instant start-up of the clock signal from a stopped state. This design option also has problems that make for a less than ideal solution. While this approach solves the delay time for starting or stopping the clock, it still requires external resistor and capacitor components which add to the package space requirements. An RC oscillator also requires additional pins for the circuit, typically 2 output and 1 input pin. Driver circuits used to output the RC clock signals tend to be larger than what would be used to drive internal signals. Thus, the RC oscillator circuit requires more power than an internally generated clock or driver signal. Further, variations between the components in the RC network also introduce variations in the clock frequency. Ways of reducing these variations are possible, but can be costly.

Ring oscillators have been used as an easy way to make an oscillating signal, and have been incorporated in many electronic circuits. The ring oscillator is commonly used in integrated circuit designs where an exact clock signal is not required. In systems, such as Flash memory systems, a ring oscillator can be used that would allow the system to function. Large performance variations, however, would be seen by the system as the ring oscillator varied over process differences, voltage variations and temperature excursions. In most cases the resultant wide range of operating parameter frequencies would be intolerable and would make for a noncompetitive product.

Systems which do not require the accuracy of a crystal oscillator can be operated using either a RC oscillator or a ring oscillator. A Flash memory system is an example of a system where some variation in timing can be tolerated, if lower cost and power savings can be realized. The ring oscillator is the most attractive because it requires less power, less pins and has fast start-stop gating. The huge drawback of this approach is the wide variations in clock signal frequency over operating parameter variables such as voltage and temperature that typically would be seen by such a system.

For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an integrated circuit which optimizes operating performance by dynamically monitoring environmental parameters and adjusting the operation and clock signal frequency.

SUMMARY OF THE INVENTION

The above mentioned problems with clock signal variations and other problems are addressed by the present invention and which will be understood by reading and studying the following specification. An integrated circuit is described which adjusted to compensate for oscillator variations.

In particular, the present invention describes an integrated circuit comprising an adjustable oscillator circuit for producing a clock signal, and control circuitry for adjusting a frequency of the clock signal in response to a measured dynamic parameter of the integrated circuit. In another embodiment, a flash memory device is described which comprises an adjustable oscillator circuit for producing a clock signal, internal circuitry for measuring a dynamic parameter of the memory device, and control circuitry for adjusting a frequency of the clock signal in response to a measured dynamic parameter. In both embodiments, the dynamic parameter can be either, or both a temperature of the integrated circuit, or a supply voltage level of the integrated circuit.

In yet another embodiment, a method is described for operating a memory circuit having an adjustable oscillator circuit for providing a clock signal. The method comprises the steps of calibrating the adjustable oscillator circuit to provide a clock signal having a predetermined frequency, detecting a dynamic parameter of the memory circuit, and adjusting the adjustable oscillator in response to the detected dynamic parameter to change the frequency of the clock signal.

A method is described for operating a memory device comprising a clock circuit for providing a clock signal having a frequency, the memory device being designed to operate over an environmental parameter having lower, nominal, and upper levels. The method comprising the steps of adjusting the clock circuit so that the frequency of the clock signal is at a predetermined level when the environmental parameter is at the nominal level, detecting a level of the environmental parameter, and adjusting the frequency of the clock signal based upon the detected level of the environmental parameter. The method also includes the steps of monitoring the operation of the memory device to detect operating errors, resetting the clock circuit to the predetermined level if errors are detected, detecting a new level of the environmental parameter after the clock circuit has been reset, and adjusting the frequency of the clock signal based upon the detected new level of the environmental parameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a block diagram of a flash memory system

FIG. 1B is a detailed diagram of the flash memory of FIG. 1A;

FIG. 1C is a detailed diagram of a flash memory card;

FIG. 2 is a schematic diagram of a prior art ring oscillator;

FIG. 3 is a schematic diagram of an adjustable ring oscillator;

FIG. 4 is a schematic diagram of a ring oscillator adjustment circuit; and

FIG. 5 is a schematic diagram of a temperature detector circuit;

FIG. 6 is a schematic diagram of a voltage detector circuit;

FIG. 7A is a block diagram of an integrated circuit incorporating a detection circuit;

FIG. 7B is a block diagram of an alternate integrated circuit incorporating a detection circuit;

FIG. 7C is a block diagram of a system having a detection circuit;

FIG. 8 is a diagram of a prior art clock divide circuit; and

FIG. 9 is a diagram of a clock divide circuit of the pres