Capacitive touch control system with frequency booster
There is provided a capacitive touch control system adapted to detect low frequency signals, including a touch panel and an analog front end. The analog front end includes a frequency booster, which boosts a low frequency signal outputted by the touch panel using a variable reference frequency corresponding to different function symbols of the low frequency signal such that resistance of a resistor of an amplifier in the analog front end needs not to be increased thereby reducing the manufacturing cost and a leakage voltage drop on the resistor.
1. A capacitive touch control system, comprising:
a touch panel;
an analog front end, configured to receive a low frequency signal from the touch panel, and comprising:
a frequency booster, configured to perform frequency adjustment on the low frequency signal using a reference frequency, wherein when the touch panel is touched by a touch pen, the reference frequency is controlled to be variable;
an operational amplifier, coupled to an output of the frequency booster, and having an inverting input end coupled to the frequency booster and a non-inverting input end; and
a gain capacitor coupled between the frequency booster and the inverting input end of the operational amplifier.
2. The capacitive touch control system as claimed in claim 1 , wherein
the low frequency signal comprises a beacon symbol and multiple function symbols, and at least one of a length and a frequency of the beacon symbol is different from multiple lengths and multiple frequencies of the multiple function symbols.
3. The capacitive touch control system as claimed in claim 2 , wherein
the reference frequency is changed corresponding to the beacon symbol and the multiple function symbols.
4. The capacitive touch control system as claimed in claim 3 , further comprising a digital backend configured to
control the reference frequency to be equal to the frequency of the beacon symbol upon identifying that the touch panel does not output the low frequency signal.
5. The capacitive touch control system as claimed in claim 3 , wherein
there are blank intervals between the multiple function symbols, which do not contain any symbol, and
within the blank intervals, the reference frequency is arranged to be equal to the frequency of the beacon symbol.
6. The capacitive touch control system as claimed in claim 3 , wherein
there are blank intervals between the multiple function symbols, which do not contain any symbol, and
within the blank intervals, the reference frequency is arranged to be equal to a frequency of a previous function symbol.
7. The capacitive touch control system as claimed in claim 2 , further comprising a digital backend configured to
recognize the beacon symbol according to the length and the frequency of the beacon symbol, and
identify that the touch panel outputs the low frequency signal upon recognizing the beacon symbol.
8. The capacitive touch control system as claimed in claim 1 , wherein the analog front end further comprises:
a feedback resistor, coupled between the inverting input end and an output end of the operational amplifier; and
a compensation capacitor, coupled between the inverting input end and the output end of the operational amplifier.
9. The capacitive touch control system as claimed in claim 8 , wherein
capacitance of the gain capacitor is smaller than that of the compensation capacitor.
10. A capacitive touch control system, comprising:
a touch panel;
an analog front end, configured to receive a low frequency signal from the touch panel, and comprising:
a frequency booster, configured to perform frequency adjustment on the low frequency signal using a reference frequency;
an operational amplifier, coupled to an output of the frequency booster, and having an inverting input end coupled to the frequency booster and a non-inverting input end; and
a gain capacitor coupled between the frequency booster and the inverting input end of the operational amplifier, wherein
when the low frequency signal is received by the analog front end in at least one interval, the reference frequency is controlled to be variable, and
when the low frequency signal is not received by the analog front end in at least one interval, the reference frequency is controlled to be constant.
11. The capacitive touch control system as claimed in claim 10 , further comprising a digital backend configured to identify a touch pen on the touch penal according to a beacon symbol of the low frequency signal sent from the touch pen.
12. The capacitive touch control system as claimed in claim 11 , wherein the digital backend is configured to control the reference frequency as a constant value before recognizing the beacon symbol of the low frequency signal sent from the touch pen.
13. The capacitive touch control system as claimed in claim 11 , wherein the digital backend is configured to control the reference frequency to be equal to a frequency of the beacon symbol before recognizing the beacon symbol of the low frequency signal sent from the touch pen.
14. The capacitive touch control system as claimed in claim 11 , wherein
the low frequency signal further comprises multiple function symbols corresponding to multiple functions of the touch pen, and at least one of multiple lengths and multiple frequencies of the multiple function symbols are different from one other.
15. The capacitive touch control system as claimed in claim 14 , wherein the reference frequency is changed corresponding to the multiple function symbols.
16. The capacitive touch control system as claimed in claim 14 , wherein
there are blank intervals between the multiple function symbols, which do not contain any symbol, and
within the blank intervals, the reference frequency is arranged to be equal to a frequency of the beacon symbol.
17. A capacitive touch control system, comprising:
a touch panel;
an analog front end, configured to receive a low frequency signal, which comprises multiple signal frequencies and multiple blank intervals each between two signal frequencies, from the touch panel, and comprising:
a frequency booster, configured to perform frequency adjustment on the low frequency signal using a reference frequency, wherein
when the multiple signal frequencies of the low frequency signal is received by the analog front end, the reference frequency is controlled to be variable, and
the reference frequency is controlled to be constant within the multiple blank intervals.