Reduced capacitive baseline shift using null time periods

1. A method comprising:

acquiring, responsive to driving a first sensing signal having a first sensing frequency onto a first group of a plurality of sensor electrodes within a first burst period, first capacitive measurements of first resulting signals received by a second group of the plurality of sensor electrodes, wherein acquiring first capacitive measurements comprises receiving a predefined number of current pulses during the first burst period;

driving, responsive to determining to increase a sensing frequency from the first sensing frequency to a second sensing frequency, a second sensing signal having the second sensing frequency onto a third group of the plurality of sensor electrodes within a second burst period having a same length as the first burst period; and

acquiring, responsive to driving the second sensing signal, second capacitive measurements of second resulting signals received by a fourth group of the plurality of sensor electrodes,

wherein acquiring second capacitive measurements comprises inserting, based at least on the second sensing frequency, one or more null time periods within the second burst period such that the same number of current pulses is received during the second burst period.

2. The method of claim 1 , wherein a first baseline capacitive measurement acquired using the first sensing signal corresponds to a first average current value, and

wherein a second baseline capacitive measurement acquired using the second sensing signal corresponds to a second average current value that is substantially equal to the first average current value.

3. The method of claim 1 , wherein the one or more null time periods are located at a beginning or at an end of the second burst period.

4. The method of claim 1 , wherein the one or more null time periods comprise a plurality of null time periods that are evenly distributed throughout the second burst period.

5. The method of claim 4 , wherein the second sensing signal comprises a plurality of transmit periods at the second sensing frequency, and

wherein inserting one or more null time periods within the second burst period comprises not driving every k-th transmit period of the plurality of transmit periods, where k is a selected integer value.

6. The method of claim 5 , further comprising:

determining a minimum value of k according to:

k

m

⁢

⁢

i

⁢

⁢

n

=

⌊

T

SENSE

,

2

T

SENSE

,

1

-

T

SENSE

,

2

⌋

 wherein T SENSE,1 represents a first sensing period associated with the first sensing frequency, wherein T SENSE,2 represents a second sensing period associated with the second sensing frequency, and wherein the brackets represent a floor function.

7. The method of claim 1 , further comprising:

disabling one or more of a transmitter and a demodulator during the one or more null time periods.

8. An input device comprising:

a plurality of sensor electrodes; and

a processing system configured to:

acquire, responsive to driving a first sensing signal having a first sensing frequency onto a first group of the plurality of sensor electrodes within a first burst period, first capacitive measurements of first resulting signals received by a second group of the plurality of sensor electrodes, wherein acquiring first capacitive measurements comprises receiving a predefined number of current pulses during the first burst period;

drive, responsive to determining to increase a sensing frequency from the first sensing frequency to a second sensing frequency, a second sensing signal having the second sensing frequency onto a third group of the plurality of sensor electrodes within a second burst period having a same length as the first burst period; and

acquire, responsive to driving the second sensing signal, second capacitive measurements of second resulting signals received by a fourth group of the plurality of sensor electrodes,

wherein acquiring second capacitive measurements comprises inserting, based at least on the second sensing frequency, one or more null time periods within the second burst period such that the same number of current pulses is received during the second burst period.

9. The input device of claim 8 , wherein a first baseline capacitive measurement acquired using the first sensing signal corresponds to a first average current value, and

wherein a second baseline capacitive measurement acquired using the second sensing signal corresponds to a second average current value that is substantially equal to the first average current value.

10. The input device of claim 8 , wherein the one or more null time periods are located at a beginning or at an end of the second burst period.

11. The input device of claim 8 , wherein the one or more null time periods comprise a plurality of null time periods that are evenly distributed throughout the second burst period.

12. The input device of claim 11 , wherein the second sensing signal comprises a plurality of transmit periods at the second sensing frequency, and

wherein inserting one or more null time periods within the second burst period comprises not driving every k-th transmit period of the plurality of transmit periods, where k is a selected integer value.

13. The input device of claim 12 , wherein the processing system is further configured to:

determine a minimum value of k according to:

k

m

⁢

⁢

i

⁢

⁢

n

=

⌊

T

SENSE

,

2

T

SENSE

,

1

-

T

SENSE

,

2

⌋

 wherein T SENSE,1 represents a first sensing period associated with the first sensing frequency, wherein T SENSE,2 represents a second sensing period associated with the second sensing frequency, and wherein the brackets represent a floor function.

14. The input device of claim 8 , wherein the processing system is further configured to:

disable one or more of a transmitter and a demodulator during the one or more null time periods.

15. A processing system comprising:

a sensor module comprising circuitry for operating a plurality of sensor electrodes, the sensor module configured to:

acquire, responsive to driving a first sensing signal having a first sensing frequency onto a first group of the plurality of sensor electrodes within a first burst period, first capacitive measurements of first resulting signals received by a second group of the plurality of sensor electrodes, wherein acquiring first capacitive measurements comprises receiving a predefined number of current pulses during the first burst period;

drive, responsive to determining to increase a sensing frequency from the first sensing frequency to a second sensing frequency, a second sensing signal having the second sensing frequency onto a third group of the plurality of sensor electrodes within a second burst period having a same length as the first burst period; and

acquire, responsive to driving the second sensing signal, second capacitive measurements of second resulting signals received by a fourth group of the plurality of sensor electrodes,

wherein acquiring second capacitive measurements comprises inserting, based at least on the second sensing frequency, one or more null time periods within the second burst period such that the same number of current pulses is received during the second burst period.

16. The processing system of claim 15 , wherein a first baseline capacitive measurement acquired using the first sensing signal corresponds to a first average current value, and

wherein a second baseline capacitive measurement acquired using the second sensing signal corresponds to a second average current value that is substantially equal to the first average current value.

17. The processing system of claim 15 , wherein the one or more null time periods comprise one of: (i) a null time period located at a beginning of the second burst period, (ii) a null time period located at an end of the second burst period, and (iii) a plurality of null time periods that are evenly distributed throughout the second burst period.

18. The processing system of claim 17 , wherein the one or more null time periods comprise (iii) a plurality of null time periods that are evenly distributed throughout the second burst period,

wherein the second sensing signal comprises a plurality of transmit periods at the second sensing frequency, and

wherein inserting one or more null time periods within the second burst period comprises not driving every k-th transmit period of the plurality of transmit periods, where k is a selected integer value.

19. The processing system of claim 18 , wherein the sensor module is further configured to:

determine a minimum value of k according to:

k

m

⁢

⁢

i

⁢

⁢

n

=

⌊

T

SENSE

,

2

T

SENSE

,

1

-

T

SENSE

,

2

⌋

 wherein T SENSE,1 represents a first sensing period associated with the first sensing frequency, wherein T SENSE,2 represents a second sensing period associated with the second sensing frequency, and wherein the brackets represent a floor function.

20. The processing system of claim 15 , wherein the sensor module is further configured to:

disable one or more of a transmitter and a demodulator during the one or more null time periods.