This disclosure relates to position indication, and more particularly to an active position indicator.
A conventional active position indicator disclosed in U.S. Pat. No. 8,199,132 is adapted to receive, using a receiving electrode, a driving signal transmitted by a position detector, amplifies and inverts the received driving signal to generate an output signal, and transmits the output signal using a transmitting electrode. As a result, the position detector can detect a position of the conventional active position indicator relative to the position detector.
The conventional active position indicator advantageously has a relatively small tip as compared to a passive position indicator, but has the following drawbacks:
1. In order to prevent the output signal from oscillating continuously due to positive feedback, a phase difference between the output signal transmitted by the transmitting electrode and the driving signal received by the receiving electrode must be as close as possible to 180 degrees, and a shielding member is required to minimize signal coupling from the transmitting electrode to the receiving electrode. Therefore, it is relatively hard to design the conventional active position indicator.
2. Boost conversion is required. Therefore, the conventional active position indicator has relatively large power consumption.
3. The conventional active position indicator is turned on/off manually by a user. Therefore, it will keep on consuming power when the user forgets to turn it off.
Therefore, an object of this disclosure is to provide a position indicator that can prevent an output signal transmitted thereby from oscillating continuously due to positive feedback.
According to this disclosure, there is provided a position indicator operatively associated with a position detector that transmits a driving signal. The position indicator includes a signal processing module. The signal processing module includes a receiving electrode, an amplifying circuit, an oscillating circuit and a transmitting electrode. The receiving electrode is adapted to receive the driving signal. The amplifying circuit is coupled to the receiving electrode, and amplifies the driving signal received by the receiving electrode to generate an amplified signal. The oscillating circuit is coupled to the amplifying circuit for receiving the amplified signal therefrom, and generates an output signal that oscillates for a time period upon satisfaction of a predetermined threshold condition associated at least with the amplified signal and a predetermined trigger level. The transmitting electrode is coupled to the oscillating circuit, and is adapted to transmit the output signal generated by the oscillating circuit.
Other features and advantages of this disclosure will become apparent in the following detailed description of the embodiment(s) with reference to the accompanying drawings, of which:
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The receiving electrode 111 is adapted to receive the driving signal transmitted by the position detector 2, among others, if any.
The amplifying circuit 112 is coupled to the receiving electrode 111, and amplifies the driving signal received by the receiving electrode 111 to generate an amplified signal. In this embodiment, the amplifying circuit 112 is a band-pass amplifying circuit, and includes a band-pass filter 1121 and an amplifying unit 1122. The band-pass filter 1121 has a pass band covering a frequency of the driving signal transmitted by the position detector 2, is coupled to the receiving electrode 111, and band-pass filters the signal(s) received by the receiving electrode 111, including the driving signal, to generate a filtered signal. The amplifying unit 1122 is coupled to the band-pass filter 1121 for receiving the filtered signal therefrom, and amplifies the filtered signal to generate the amplified signal.
The pressure sensor 113 is adapted to sense a contact pressure between the receiving electrode 111 and the position detector 2 to generate a pressure sensing signal. In this embodiment, the pressure sensor 113 is a micro-electro-mechanical system (MEMS) pressure sensor, and is thus relatively stable and precise. However, this disclosure is not limited to this type of pressure sensor.
The processing circuit 114 is coupled to the pressure sensor 113 for receiving the pressure sensing signal therefrom. Based on the pressure sensing signal, the processing circuit 114 estimates the contact pressure between the receiving electrode 111 and the position detector 2 to obtain an estimated pressure value, and generates an oscillation control signal associated with whether the receiving electrode 111 contacts the position detector 2 or not.
The oscillating circuit 115 is coupled to the amplifying unit 1122 of the amplifying circuit 112 and the processing circuit 114 for receiving the amplified signal and the oscillation control signal respectively therefrom, and generates an output signal based on the amplified signal, the oscillation control signal and a predetermined trigger level, such that the output signal begins to oscillate for a time period upon satisfaction of a predetermined threshold condition associated with the amplified signal, the oscillation control signal and the trigger level. In this embodiment, the oscillating circuit 115 includes a resistor 1151, a first switch 1152, a second switch 1153, a transformer 1154 and a capacitor 1157. The resistor 1151 has a first terminal that is coupled to the amplifying unit 1122 of the amplifying circuit 112 for receiving the amplified signal therefrom, and a second terminal. The first switch 1152 is coupled to the second terminal of the resistor 1151, and is operable between an ON state and an OFF state based on a voltage at the second terminal of the resistor 1151. The second switch 1153 is coupled to the processing circuit 114 for receiving the oscillation control signal therefrom, and is operable between an ON state and an OFF state based on the oscillation control signal. The transformer 1154 has a primary winding 1155 that is coupled to the first and second switches 1152, 1153 in series, and a secondary winding 1156 that provides the output signal for assisting the position detector 2 in determining a position of the position indicator 1 relative to the position detector 2. The capacitor 1157 is coupled to the secondary winding 1156 of the transformer 1154 in parallel. When the first and second switches 1152, 1153 both operate in the ON state, the output signal oscillates at a predetermined frequency for the time period. This frequency is determined by an inductance of the secondary winding 1156 and a capacitance of the capacitor 1157, is higher than or equal to that of the driving signal transmitted by the position detector 2. In some embodiments, the frequency of the output signal may be outside the pass band of the band-pass filter 1121 to assist in alleviating/preventing the positive feedback.
The transmitting electrode 116 is coupled to the secondary winding 1156 of the transformer 1154 of the oscillating circuit 115, and is adapted to transmit the output signal.
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In this embodiment, the third switch 121 is a normally OFF switch, and operates in the ON state when actuated by a user. Moreover, the power circuit 122 includes a fourth switch 1221, a control unit 1222 and a voltage regulator 1223. The fourth switch 1221 is coupled to the first terminal of the third switch 121, and receives the source voltage (Vin). The control unit 1222 is coupled to the second terminal of the third switch 121 and to the fourth switch 1221, receives the power control signal, and controls, based on the operating state of the third switch 121 and the power control signal, operation of the fourth switch 1221 between an ON state and an OFF state such that the fourth switch 1221 operates in the ON state to permit transmission of the source voltage (Vin) therethrough for a duration that the third switch 121 operates in the ON state or for the duration that the power control signal is at the first level. The voltage regulator 1223 is coupled to the fourth switch 1221 for receiving the source voltage (Vin) therefrom, and regulates the received source voltage (Vin) to generate the power supply voltage (Vdd).
The processing circuit 114 is coupled further to the second terminal of the third switch 121 and the control unit 1222 of the power circuit 122, and generates the power control signal for the control unit 1222 of the power circuit 122 based on the operating state of the third switch 121 and the pressure sensing signal. In this embodiment, the processing circuit 114 performs the following: counting from a predetermined initial value to a predetermined target value; when(ever) the third switch 121 operates in the ON state, setting the power control signal to the first level, and setting the counting to the predetermined initial value (i.e., the counting is set at the predetermined initial value during the duration that the third switch 121 operates in the ON state); when(ever) it is determined, based on the pressure sensing signal, that the receiving electrode 111 contacts the position detector 2, setting the counting to the predetermined initial value; and when the counting completes at the predetermined target value, setting the power control signal to the second level to cause said fourth switch 1221 to operate in the OFF state.
In application, when the third switch 121 is actuated for the first time, the power circuit 122 outputs the power supply voltage (Vdd), and the processing circuit 114 sets the power control signal to the first level. Then, when the third switch 121 is not actuated and the receiving electrode 111 does not contact the position detector 2 (see
In view of the above, the position indicator 1 of this embodiment has the following advantages:
1. Regardless of the frequency the output signal oscillates at, continuous oscillation of the output signal due to positive feedback can be prevented by at least one of adequately setting the trigger level and the band-pass filter 1121. Therefore, it is relatively easy to design the position indicator 1.
2. Since boost conversion is not required, the position indicator 1 has relatively small power consumption.
3. Since the output of the power supply voltage (Vdd) may be stopped automatically, the position indicator 1 of this embodiment will not keep on consuming power due to negligence of the user.
While this disclosure has been described in connection with what is(are) considered the exemplary embodiment(s), it is understood that this disclosure is not limited to the disclosed embodiment(s) but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.