Increasing low-force accuracy at a device
Methods and devices are disclosed for increasing low-force accuracy at a device, such as a pen or a stylus which are used for communicating with a digitizer. An example method describes detecting an amount of force at the tip of the device and generating a voltage associated with the amount of force. The example method further includes logarithmically sampling the voltage to produce a digital value associated with the amount of force and determining whether the device is operating in an inking state based on the digital value. An example device may include a pressure sensor to detect an amount of force and generate a voltage associated with the amount of force, a sampling circuit to sample the voltage to produce a digital value, a memory and a processor in communication with the memory to determine whether the device is operating in an inking state based on the digital value.
1. A method of increasing low-force accuracy at a device for communicating with a digitizer, comprising:
detecting, by a pressure sensor in the device, an amount of force at the tip of the device;
generating, by the pressure sensor, a first voltage and a second voltage associated with the amount of force;
calculating a differential voltage between the first voltage and the second voltage;
amplifying the differential voltage to obtain an amplified voltage;
logarithmically sampling the amplified voltage to produce a digital value associated with the amount of force; and
determining whether the device is operating in an inking state based on the digital value or sending the digital value to the digitizer.
2. The method of claim 1 , wherein the amplifying of the differential voltage comprises:
amplifying, by a linear amplifier, the differential voltage to produce the amplified voltage, wherein the amplified voltage is greater than the differential voltage; and
wherein logarithmically sampling the amplified voltage comprises:
sampling, by a logarithmic analog-to-digital converter (ADC), the differential voltage to produce the digital value.
3. The method of claim 2 , determining whether the device is operating in the inking state further comprises:
comparing the digital value with a threshold value; and
determining that the device is operating in the inking state when the digital value is equal to or greater than the threshold value.
4. The method of claim 1 , wherein the amplifying of the differential voltage comprises:
amplifying, by a logarithmic amplifier, the differential voltage to produce the amplified voltage, wherein the amplified voltage is greater than the differential voltage; and
wherein logarithmically sampling the amplified voltage comprises:
sampling, by a linear analog-to-digital converter (ADC), the differential voltage to produce the digital value.
5. The method of claim 4 , determining whether the device is operating in the inking state further comprises:
comparing the digital value with a threshold value; and
determining that the device is operating in the inking state when the digital value is equal to or greater than the threshold value.
6. The method of claim 1 , wherein the pressure sensor is a strain gauge sensor.
7. The method of claim 1 , wherein the device is a pen or a stylus and the pressure sensor is positioned at or near the tip of the pen or the stylus.
8. The method of claim 1 , wherein the pressure sensor is a microelectromechanical system (MEMS) sensor.
9. The method of claim 1 , wherein the pressure sensor is a capacitive force sensor.
10. A device for increasing low-force accuracy at a device for communicating with a digitizer, comprising:
a pressure sensor configured to detect an amount of force at the tip of the device and generate a first voltage and a second voltage associated with the amount of force;
a sampling circuit configured to:
calculate a differential voltage between the first voltage and the second voltage;
amplify the differential voltage to obtain an amplified voltage; and
logarithmically sample the amplified voltage to produce a digital value associated with the amount of force;
a memory; and
a processor in communication with the memory, wherein the processor is configured to:
determine whether the device is operating in an inking state based on the digital value or send the digital value to the digitizer.
11. The device of claim 10 , wherein the sampling circuit includes:
a linear amplifier configured to amplify the differential voltage to produce the amplified voltage, wherein the amplified voltage is greater than the differential voltage; and
a logarithmic analog-to-digital converter (ADC) configured to logarithmically sample the differential voltage to produce the digital value.
12. The device of claim 11 , wherein the processor is further configured to:
compare the digital value with a threshold value; and
determine that the device is operating in the inking state when the digital value is equal to or above the threshold value.
13. The device of claim 10 , wherein the sampling circuit includes:
a logarithmic amplifier configured to amplify the differential voltage to produce the amplified voltage, wherein the amplified voltage is greater than the differential voltage; and
a linear analog-to-digital converter (ADC) configured to sample the differential voltage to produce the digital value.
14. The device of claim 13 , wherein the processor is further configured to:
compare the digital value with a threshold value; and
determine that the device is operating in the inking state when the digital value is equal to or above the threshold value.
15. The device of claim 10 , wherein the pressure sensor is a strain gauge sensor.
16. The device of claim 10 , wherein the device is a pen or a stylus and the pressure sensor is located at or near the tip of the pen or the stylus.
17. The device of claim 10 , wherein the pressure sensor is a microelectromechanical system (MEMS) sensor.
18. The device of claim 10 , wherein the pressure sensor is a capacitive force sensor.