Sensing objects using multiple transmitter frequencies

1. A processing system comprising:

a sensor module coupled to a plurality of sensor electrodes, the sensor module configured to:

drive the plurality of sensor electrodes with first sensing signals at a strict subset of a plurality of frequencies, and

drive the plurality of sensor electrodes with second sensing signals at a remaining subset of the plurality of frequencies; and

a determination module configured to:

obtain, concurrently with the driving of the plurality of sensor electrodes with the first sensing signals, a first plurality of measurement values that are based on effects of the first sensing signals,

identify, from the first plurality of measurement values, a first input object in a sensing region that is less than a first size threshold indicating possible resonance of the first input object,

obtain, concurrently with the driving of the plurality of sensor electrodes with the second sensing signals, a second plurality of measurement values that are based on effects of the second sensing signals, and a resonance of a pen in the sensing region,

wherein the first input object is the pen, wherein the plurality of sensor electrodes are driven with the second sensing signals at the remaining subset in response to identifying the first input object in the sensing region that is less than the first size threshold,

determine a delta frequency image between the first plurality of measurement values and the second plurality of measurements values, wherein the delta frequency image comprises, for each location of a plurality of locations, a difference between a first measurement value in the first plurality of measurement values and a second measurement value in the second plurality of measurement values, the first measurement value and the second measurement value corresponding to the location,

determine a resonating state of the pen based on the first plurality of measurement values and the second plurality of measurement values,

determine positional information for the pen in the resonating state from the delta frequency image, wherein the delta frequency image suppresses noise and a second input object that is present in the sensing region and is in a non-resonating state, and

report the resonating state of the pen.

2. The processing system of claim 1 , wherein the determination module is further configured to:

determine a first signal response level of the first plurality of measurement values, and

determine a second signal response level of the second plurality of measurement values,

wherein determining the resonating state is based on the comparing the first signal response level with the second signal response level.

3. The processing system of claim 2 , wherein the first signal response level is suppressed.

4. The processing system of claim 2 , wherein the first signal response level is an elevated level.

5. The processing system of claim 2 , wherein the determination module is further configured to:

determine a difference between the first signal response level and the second signal response level,

wherein the resonating state is determined based on the difference being greater than a detection threshold.

6. The processing system of claim 1 , wherein the pen is reported to the host and the second input object is not reported to the host.

7. The processing system of claim 1 , wherein the second input object is at least a portion of a hand.

8. The processing system of claim 1 , further comprising:

determining a delta baseline image between the first plurality of measurement values and a baseline;

detecting the second input object in the sensing region using the delta baseline image;

determining that the second input object satisfies a second size threshold using the delta baseline image,

wherein the pen and the second input object are reported to the host based on the pen being in the resonating state and the second input object satisfying the second size threshold.

9. A method for sensing input objects, comprising:

driving a plurality of sensor electrodes with first sensing signals at a strict subset of a plurality of frequencies;

obtaining, concurrently with the driving of the plurality of sensor electrodes with the first sensing signals, a first plurality of measurement values that are based on effects of the first sensing signals;

identifying, from the first plurality of measurement values, a first input object in a sensing region that is less than a first size threshold indicating possible resonance of the first input object;

driving the plurality of sensor electrodes with second sensing signals at a remaining subset of the plurality of frequencies, wherein the plurality of sensor electrodes are driven with the second sensing signals at the remaining subset in response to identifying the first input object in the sensing region that is less than the first size threshold;

obtaining, concurrently with the driving of the plurality of sensor electrodes with the second sensing signals, a second plurality of measurement values that are based on effects of the second sensing signals, and a resonance of a pen in the sensing region, wherein the first input object is the pen;

determining a delta frequency image between the first plurality of measurement values and the second plurality of measurement values, wherein the delta frequency image comprises, for each location of a plurality of locations, a difference between a first measurement value in the first plurality of measurement values and a second measurement value in the second plurality of measurement values, the first measurement value and the second measurement value corresponding to the location;

determining a resonating state of the pen based on the first plurality of measurement values and the second plurality of measurement values;

determining positional information for the pen in the resonating state from the delta frequency image, wherein the delta frequency image suppresses noise and a second input object that is present in the sensing region and is in a non-resonating state; and

reporting the resonating state of the pen.

10. The method of claim 9 , further comprising:

determining a first signal response level of the first plurality of measurement values, and

determining a second signal response level of the second plurality of measurement values,

wherein determining the resonating state is based on the comparing the first signal response level with the second signal response level.

11. The method of claim 10 , further comprising:

determining a difference between the first signal response level and the second signal response level,

wherein the resonating state is determined based on the difference being greater than a detection threshold.

12. The method of claim 9 , further comprising:

determining a delta baseline image between the first plurality of measurement values and a baseline;

detecting the second input object in the sensing region using the delta baseline image;

determining that the second input object satisfies a second size threshold using the delta baseline image,

wherein the pen and the second input object are reported to the host based on the pen being in the resonating state and the second input object satisfying the second size threshold.

13. An input device comprising:

a plurality of sensor electrodes configured to generate sensing signals; and

a processing system connected to the plurality of sensor electrodes and configured to:

drive the plurality of sensor electrodes with first sensing signals at a strict subset of a plurality of frequencies,

obtain, concurrently with the driving of the plurality of sensor electrodes with the first sensing signals, a first plurality of measurement values that are based on effects of the first sensing signals;

identify, from the first plurality of measurement values, a first input object in a sensing region that is less than a first size threshold indicating possible resonance of the first input object;

drive the plurality of sensor electrodes with second sensing signals at a remaining subset of the plurality of frequencies, wherein the plurality of sensor electrodes are driven with the second sensing signals at the remaining subset in response to identifying the first input object in the sensing region that is less than the first size threshold,

obtain, concurrently with the driving of the plurality of sensor electrodes with the second sensing signals, a second plurality of measurement values that are based on effects of the second sensing signals, and a resonance of a pen in the sensing region, wherein the first input object is the pen,

determine a delta frequency image between the first plurality of measurement values and the second plurality of measurement values, wherein the delta frequency image comprises, for each location of a plurality of locations, a difference between a first measurement value in the first plurality of measurement values and a second measurement value in the second plurality of measurement values, the first measurement value and the second measurement value corresponding to the location;

determine a resonating state of the pen based on the first plurality of measurement values and the second plurality of measurement values,

determine positional information for the pen in the resonating state from the delta frequency image, wherein the delta frequency image suppresses noise and a second input object that is present in the sensing region and is in a non-resonating state, and

report the resonating state of the pen.