Force sensing system and method
A force sensing system for determining if a user input has occurred, the system comprising: an input channel, to receive an input from at least one force sensor; an activity detection stage, to monitor an activity level of the input from the at least one force sensor and, responsive to an activity level which may be indicative of a user input being reached, to generate an indication that an activity has occurred at the force sensor; and an event detection stage to receive said indication, and to determine if a user input has occurred based on the received input from the at least one force sensor.
1. A force sensing system for determining if a user input has occurred, the system comprising:
an input channel, to receive an input from at least one force sensor;
an activity detection stage, to monitor an activity level of the input from the at least one force sensor and, responsive to an activity level which may be indicative of a user input being reached, to generate an indication that an activity has occurred at the force sensor; and
an event detection stage to receive said indication, and to determine if a user input has occurred based on the received input from the at least one force sensor;
wherein:
the activity detection stage comprises a first threshold module, a second threshold module, and a feature extraction module;
the first threshold module is configured to determine if the activity level of the input from the at least one force sensor exceeds a first threshold value indicative of a base level of activity, and the second threshold module is configured to determine if the activity level of the input from the at least one force sensor exceeds a second threshold value;
the feature extraction module is configured to extract features from a monitored signal, the monitored signal comprising the input from the at least one force sensor;
the first threshold module is configured to operate in a deep standby mode;
the second threshold module is power gated by the first threshold module, such that the deep standby mode transitions to a standby mode and the second threshold module is enabled if the activity level of the input from the at least one force sensor exceeds the first threshold value; and
the feature extraction module is power gated by the second threshold module, such that the standby mode transitions to an active mode and the feature extraction module is enabled if the activity level of the input from the at least one force sensor exceeds the second threshold value.
2. A device comprising the force sensing system as claimed in claim 1 , preferably wherein the device comprises a mobile phone or tablet device.
3. A force sensing method, the method comprising the following steps:
receiving an input from at least one force sensor;
monitoring an activity level of the input from the at least one force sensor and, responsive to an activity level which may be indicative of a user input being reached, to generating an indication that an activity has occurred at the force sensor; and
determining if a user input has occurred based on the received input from the at least one force sensor;
wherein the method further comprises:
using a first threshold module, a second threshold module, and a feature extraction module to monitor the activity level of the input from the at least one force sensor, wherein the first threshold module is configured to determine if the activity level of the input from the at least one force sensor exceeds a first threshold value indicative of a base level of activity, wherein the second threshold module is configured to determine if the activity level of the input from the at least one force sensor exceeds a second threshold value, and wherein the feature extraction module is configured to extract features from a monitored signal, the monitored signal comprising the input from the at least one force sensor;
operating the first threshold module in a deep standby mode;
power gating the second threshold module by the first threshold module, such that the deep standby mode transitions to a standby mode and the second threshold module is enabled if the activity level of the input from the at least one force sensor exceeds the first threshold value; and
power gating the feature extraction module by the second threshold module, such that the standby mode transitions to an active mode and the feature extraction module is enabled if the activity level of the input from the at least one force sensor exceeds the second threshold value.
4. The system of claim 1 , configured to transition from the deep standby mode, to the standby mode and then to the active mode with an increasing activity level of the input from the at least one force sensor, and to enable at least one module of the force sensing system from a disabled or a low-power state with each transition.
5. The system of claim 4 , configured such that a sample frequency, data acquisition rate, scan rate or sample rate at which the at least one force sensor is sampled is dependent on the mode of operation.
6. The system of claim 1 , configured to transition between the deep standby mode, the standby mode and the active mode dependent on the activity level of the input from the at least one force sensor, and configured such that a sample frequency, data acquisition rate, scan rate or sample rate at which the at least one force sensor is sampled is dependent on the mode of operation.
7. The system of claim 1 , wherein:
the first threshold value is a fixed threshold value; and
the second threshold value is a noise threshold value and/or an adaptive threshold value.
8. The system of claim 7 , wherein the second threshold module is configured to derive the noise threshold value adaptively based on a running estimate of noise in the input from the at least one force sensor.
9. The system of claim 1 , configured such that a sample frequency, data acquisition rate, scan rate or sample rate at which at least one force sensor is sampled is dependent on the mode of operation.
10. The system of claim 9 , wherein a very low sample rate is used in the deep standby mode, a low sample rate is used in the standby mode, and a high sample rate is used in the active mode.
11. The system of claim 1 , wherein the second threshold module and the feature extraction module are configured to be disabled or placed in a low-power state unless the system is in the standby mode or the active mode.
12. The system of claim 11 , wherein the feature extraction module is configured to be disabled or placed in a low-power state unless the system is in the active mode.
13. The system of claim 1 , wherein:
the indication generated by the activity detection stage and received by the event detection stage comprises at least one output of the feature extraction module; and/or
if the activity level exceeds the second threshold value, the activity detection stage determines that an activity has occurred at the at least one force sensor.
14. The system of claim 1 , further comprising a sensor conditioning stage, to perform conditioning of an input received from the input channel to provide a conditioned force sense signal, wherein the activity detection stage performs the activity level monitoring on the conditioned force sense signal.