Methods and systems for motor control

1. A control circuit configured to connect to a motor and a clock generator circuit, comprising:

a counter circuit configured to measure a cycle time of the motor and generate a counter value that represents the cycle time;

a calibration circuit in communication with a memory, wherein the memory stores a delta clock frequency value defined as a difference between an actual frequency of the clock generator circuit and a known ideal frequency of the clock generator circuit;

wherein the calibration circuit is configured to compute a compensated value using the delta clock frequency; and

a conversion circuit connected to the calibration circuit and configured to:

receive the compensated value; and

compute a rotational speed of the motor according to the compensated value and the counter value;

wherein the control circuit operates the motor according to the computed rotational speed.

2. The control circuit according to claim 1 , wherein the counter circuit is connected to an input terminal of the conversion circuit and configured to transmit the counter value to the conversion circuit.

3. The control circuit according to claim 2 , wherein the conversion circuit is further configured to compute the rotational speed of the motor based on the counter value.

4. The control circuit according to claim 1 , wherein the control circuit further comprises a feedback control circuit connected to an output terminal of the conversion circuit.

5. The control circuit according to claim 4 , wherein the control circuit is further configured to receive a pulse width modulation input signal and generate a target rotational speed according to the pulse width modulation input signal.

6. The control circuit according to claim 5 , wherein the feedback control circuit is configured to:

receive the target rotational speed and the computed rotational speed; and

generate a drive signal according to the target rotational speed and the computed rotational speed.

7. The control circuit according to claim 1 , wherein the compensated value is represented as a binary number having a predetermined number of bits and the memory stores the predetermined number of bits.

8. The control circuit according to claim 1 , wherein the compensated value is represented as a binary number having a predetermined number of bits and the memory stores only a portion of the bits.

9. A method for operating a motor system with a motor, comprising:

supplying the motor system with a clock signal having a known ideal frequency and an actual frequency;

determining a frequency deviation comprising:

measuring the actual frequency of the clock signal; and

computing a change in frequency defined as a difference between the ideal frequency and the measured actual frequency;

calibrating the motor system comprising:

computing a compensated value according to the change in frequency, wherein the compensated value is represented as a binary number having a predetermined number of bits; and

computing a rotational speed according to the compensated value; and

controlling a rotational speed of the motor according to the computed rotational speed.

10. The method according to claim 9 , further comprising measuring a length of time of a cycle of the motor.

11. The method according to claim 9 , wherein controlling the rotational speed of the motor further comprises generating a feedback signal according to the computed rotational speed and controlling the rotational speed of the motor according to the feedback signal.

12. The method according to claim 9 , wherein calibrating the motor system comprises computing the compensated value according to a predetermined constant and the ideal frequency.

13. The method according to claim 9 , further comprising storing the predetermined number of bits to a memory.

14. The method according to claim 9 , further comprising storing only a portion of the bits to a memory.

15. A system having a motor, comprising:

a clock generator circuit configured to generate a clock signal having a known ideal frequency and an actual frequency;

a memory configured to store a delta clock frequency defined as a difference between the known ideal frequency and the actual frequency;

a control circuit connected to the motor and the clock generator circuit and having access to the memory, wherein the control circuit operates according to the actual frequency, and wherein the control circuit comprises:

a calibration circuit having access to the memory and configured to:

receive the delta clock frequency value; and

compute a compensated value according to the delta clock frequency and a predetermined constant;

a counter configured to measure a cycle time of the motor and generate a counter value according to the measured cycle time; and

a conversion circuit connected to the calibration circuit and configured to:

receive the compensated value; and

compute a rotational speed of the motor according to the compensated value and the counter value;

wherein the control circuit operates the motor according to the computed rotational speed.

16. The system according to claim 15 , wherein the control circuit further comprises a feedback control circuit connected to an output terminal of the conversion circuit.

17. The system according to claim 15 , wherein the control circuit is further configured to receive a pulse width modulation input signal and generate a target rotational speed according to the pulse width modulation input signal.

18. The system according to claim 15 , wherein the feedback control circuit is configured to:

receive the target rotational speed and the computed rotational speed; and

generate a drive signal according to the target rotational speed and the computed rotational speed.

19. The system according to claim 15 , further comprising a feedback circuit connected to the motor and configured to detect an actual rotational speed of the motor.