Differential sensing in an active stylus
In one embodiment, a stylus receives a first signal from a first electrode of the stylus, the stylus being operable to communicate wirelessly with a device through a touch sensor of the device; receives a second signal from a second electrode of the stylus, the second signal being a reference signal and the second electrode being a reference electrode; and compares the first signal with the second signal.
1. A method comprising:
receiving, wirelessly with a first electrode of a stylus, a first signal comprising a signal component, the stylus being operable to communicate wirelessly with a device via the first electrode and through a touch sensor of the device;
receiving a second signal from a second electrode of the stylus, the second signal comprising a signal component, the first signal and second signal each containing noise having similar characteristics, wherein the first electrode spans between a first distal end and a first proximal end along a longitudinal axis of the stylus, the second electrode spans between a second distal end and a second proximal end along the longitudinal axis of the stylus, and the first proximal end of the first electrode is located distal to the second distal end of the second electrode along the longitudinal axis of the stylus, wherein the first electrode and the second electrode are concentrically arranged about the longitudinal axis of the stylus, and wherein the signal component of the first signal is a first version of a device signal (S) and the signal component of the second signal is a second version of the device signal S;
removing noise from the first signal by subtracting the second signal from the first signal, including generating an output that is the difference between the first signal and the second signal;
determining the signal component of the first signal based on the output and the signal component of the second signal; and
synchronizing the stylus with the device using a bit sequence extracted from the determined signal component of the first signal.
2. The method of claim 1 , wherein comparing the first signal with the second signal comprises comparing the first signal with the second signal using an operational amplifier of the stylus.
3. The method of claim 1 , wherein comparing the first signal with the second signal comprises comparing the first signal with the second signal using a digital comparator of the stylus.
4. The method of claim 1 , wherein the first electrode and the second electrode interpose a third electrode in-between along the longitudinal axis of the stylus.
5. The method of claim 1 , comprising:
transmitting, wirelessly with at least one of the first electrode and the second electrode of the stylus, a third signal to the device, in response to the bit sequence transmitted by the device as a synchronization signal.
6. A non-transitory computer-readable medium comprising logic, the logic configured to, when executed by one or more processors, cause the one or more processors to perform operations comprising:
receiving, wirelessly with a first electrode of a stylus, a first signal comprising a signal component, the stylus being operable to communicate wirelessly with a device via the first electrode and through a touch sensor of the device;
receiving a second signal from a second electrode of the stylus, the second signal comprising a signal component, the first signal and second signal each containing noise having similar characteristics, wherein the first electrode spans between a first distal end and a first proximal end along a longitudinal axis of the stylus, the second electrode spans between a second distal end and a second proximal end along the longitudinal axis of the stylus, and the first proximal end of the first electrode is located distal to the second distal end of the second electrode along the longitudinal axis of the stylus wherein the first electrode and the second electrode are concentrically arranged about the longitudinal axis of the stylus, and wherein the signal component of the first signal is a first version of a device signal (S) and the signal component of the second signal is a second version of the device signal S;
removing noise from the first signal by subtracting the second signal from the first signal, including generating an output that is the difference between the first signal and the second signal;
determining the signal component of the first signal based on the output and the signal component of the second signal; and
synchronizing the stylus with the device using a bit sequence extracted from the determined signal component of the first signal.
7. The non-transitory computer-readable medium of claim 6 , wherein the first electrode is located in a tip region of the stylus.
8. The non-transitory computer-readable medium of claim 6 , wherein comparing the first signal with the second signal comprises comparing the first signal with the second signal using an operational amplifier.
9. The non-transitory computer-readable medium of claim 6 , wherein comparing the first signal with the second signal comprises comparing the first signal with the second signal using a digital comparator.
10. The non-transitory computer-readable medium of claim 6 , wherein the stylus is further operable to multiply by a gain factor the output of the comparison of the first signal with the second signal.
11. The non-transitory computer-readable medium of claim 6 , wherein the first electrode and the second electrode interpose a third electrode in-between along the longitudinal axis of the stylus.
12. The non-transitory computer-readable medium of claim 6 , wherein the operations comprise:
transmitting, wirelessly with at least one of the first electrode and the second electrode of the stylus, a third signal to the device, in response to the bit sequence transmitted by the device as a synchronization signal.
13. A stylus comprising:
a plurality of electrodes;
a non-transitory computer-readable medium comprising logic, the logic configured to, when executed by one or more processors, cause the one or more processors to perform operations comprising:
receiving, wirelessly with a first electrode of the plurality of electrodes, a first signal comprising a signal component, the signal component of the first signal having an unknown quantity, the stylus being operable to communicate wirelessly with a device via the first electrode and through a touch sensor of the device;
receiving a second signal from a second electrode of the stylus, the second signal comprising a signal component, the first signal and second signal each containing noise having similar characteristics, the signal component of the second signal associated with a known quantity, wherein the first electrode spans between a first distal end and a first proximal end along a longitudinal axis of the stylus, the second electrode spans between a second distal end and a second proximal end along the longitudinal axis of the stylus, and the first proximal end of the first electrode is located distal to the second distal end of the second electrode along the longitudinal axis of the stylus, wherein the first electrode and the second electrode are concentrically arranged about the longitudinal axis of the stylus, and wherein the signal component of the first signal is a first version of a device signal (S) and the signal component of the second signal is a second version of the device signal S;
removing noise from the first signal by subtracting the second signal from the first signal, including generating an output that is the difference between the first signal and the second signal;
determining the unknown quantity of the signal component of the first signal based on the output and the known quantity associated with the signal component of the second signal; and
synchronizing the stylus with the device using a bit sequence extracted from the determined signal component of the first signal.
14. The stylus of claim 13 , wherein the first electrode is located in the tip of the stylus.
15. The stylus of claim 13 , wherein comparing the first signal with the second signal comprises comparing the first signal with the second signal using an operational amplifier.
16. The stylus of claim 13 , wherein comparing the first signal with the second signal comprises comparing the first signal with the second signal using a digital comparator.
17. The stylus of claim 13 , wherein the stylus is further operable to multiply by a gain factor the output of the comparison of the first signal with the second signal.
18. The stylus of claim 13 , wherein determining the unknown quantity of the signal component of the first signal based on the output and the known quantity associated with the signal component of the second signal comprises summing the output and the known quantity associated with the signal component of the second signal.
19. The stylus of claim 13 , wherein the first electrode and the second electrode interpose a third electrode in-between along the longitudinal axis of the stylus.
20. The stylus of claim 13 , wherein the operations comprise:
transmitting, wirelessly with at least one of the first electrode and the second electrode of the stylus, a third signal to the device, in response to the bit sequence transmitted by the device as a synchronization signal.