Counter with correction circuitry

1. Counting circuitry for providing a corrected count value based on the number of rising and falling edges of an input signal occurring during a reference time period, the counting circuitry comprising:

a counter arranged to provide a first count value based on one of:

the number of said rising edges of said input signal occurring during said reference time period; and

the number of said falling edges of said input signal occurring during said reference time period;

wherein said counting circuitry further comprises adjustment circuitry arranged to generate a corrected count value by determining the state of said input signal at the start time and end time of said reference time period, and adjusting said first count value when the state of said input signal at the start of said reference time period is different from the state of said input signal at the end of said reference time period.

2. The counting circuitry of claim 1 , wherein said adjustment circuitry is arranged to add a value to said first count value when said input signal is at a first state at said start time and at a second state at said end time, and to subtract a value when said input signal is at said second state at said start time and at said first state at said end time.

3. The counting circuitry of claim 1 wherein said adjustment circuitry comprises multiplying means arranged to multiply said first count value by two, and adding means arranged to selectively add one and selectively subtract one from the result of said multiplication to generate said corrected count value.

4. The counting circuitry of claim 3 , wherein said counter is arranged to count the falling edges of said input signal during said reference time period, and said adjustment circuitry is arranged to add one to the result of said multiplication when said input signal is low at said start time and high at said end time, and minus one from the result of said multiplication when said input signal is high at said start time and low at said end time.

5. The counting circuitry of claim 3 , wherein said counter is arranged to count the rising edges of said input signal during said reference time period, and said adjustment means is arranged to add one to the result of said multiplication when said input signal is high at said start time and low at said end time, and minus one from the result of said multiplication when said input signal is low at said start time and high at said end time.

6. The counting circuitry of claim 1 , wherein said start and end times of said reference time period are determined by edges of a reference time signal, and said adjustment circuitry comprises:

first sampling means arranged to sample said reference time signal with falling edges of said input signal and output the result;

second sampling means arranged to sample said reference time signal with rising edges of said input signal and output the result; and

third sampling means arranged to sample the output of one of said first and second sampling means with the rising and falling edges of the output of the other one of said first and second sampling means, the generation of said corrected count value being based on the output of said third sampling means.

7. A calibration circuit for calibrating a voltage controlled oscillator, the voltage controlled oscillator generating an output oscillating signal, said calibration circuit comprising:

counting circuitry according to claim 1 , for providing a count value based on the number of rising and falling edges of said output signal of the voltage controlled oscillatory; and

a comparator for comparing said count value with a reference value and calibrating said voltage controlled oscillator based on said comparison.

8. The calibration circuit of claim 7 , wherein said voltage controlled oscillator is calibrated by shifting its operating range.

9. A mobile device comprising counting circuitry for providing a corrected count value based on the number of rising and falling edges of an input signal occurring during a reference time period, the counting circuitry comprising:

a counter arranged to provide a first count value based on one of:

the number of said rising edges of said input signal occurring during said reference time period; and

the number of said falling edges of said input signal occurring during said reference time period;

wherein said counting circuitry further comprises adjustment circuitry arranged to generate a corrected count value by determining the state of said input signal at the start time and end time of said reference time period, and adjusting said first count value when the state of said input signal at the start of said reference time period is different from the state of said input signal at the end of said reference time period.

10. A method of providing a count value based on the number of rising and falling edges of an input signal occurring during a reference time period, the method comprising:

providing a first count value based on counting one of:

the number of said rising edges of said input signal occurring during said reference time period; and

the number of said falling edges of said input signal occurring during said reference time period;

determining the state of said input signal at the start time and end time of said reference time period;

adjusting said first count value when the state of said input signal at the start of said reference time period is different from the state of said input signal at the end of said reference time period to generate a corrected count value; and

outputting the corrected count value.