Active stylus receiving circuit with interpolated sampling points and touch panel system using active stylus pen
An active stylus receiving circuit receives a vector data signal transmitted by an active stylus. The vector data signal carries vector data. The vector data includes in-phase data and quadrature data. The active stylus receiving circuit includes an analog-to-digital converter, an interpolation circuit and a demodulation circuit. The analog-to-digital converter samples and converts the vector data signal into digital signal with a plurality of sampling points. The interpolation circuit performs interpolating operation on the digital signal, so as to increase the number of sampling points representing the digital signal, and generate interpolated digital signal. The demodulation circuit performs demodulating operation on the interpolated digital signal to generate demodulated in-phase data and demodulated quadrature data, thereby obtaining demodulated vector data.
1. An active stylus receiving circuit for receiving vector data signal transmitted by an active stylus, the vector data signal carrying vector data including in-phase data and quadrature data, the active stylus receiving circuit comprising:
an analog-to-digital converter for sampling and converting the vector data signal into digital signal with a plurality of sampling points;
an interpolation circuit for performing interpolating operation on the digital signal to increase the number of sampling points representing the digital signal so as to generate interpolated digital signal; and
a demodulation circuit for performing demodulating operation on the interpolated digital signal to generate demodulated in-phase data and demodulated quadrature data, so as to obtain demodulated vector data, wherein the digital signal generated after the interpolation circuit performs interpolating operation is:
Y
(
m
)
=
{
X
(
n
)
+
X
(
n
+
1
)
2
,
m
=
2
,
4
,
6
→
∞
,
n
=
m
2
X
(
n
)
,
m
=
1
,
3
,
5
→
∞
,
n
=
floor
(
m
2
)
+
1
,
where Y( ) represents interpolated digital signal, X( ) represents digital signal outputted by the analog-to-digital converter, and floor( ) represents a floor function.
2. The active stylus receiving circuit as claimed in claim 1 , wherein the vector data signal is: xi(t)cos(πωt)+xq(t)sin(ωt), where xi(t) represents in-phase data, xq(t) represents quadrature data, cos(ωt) represents in-phase modulation carrier signal, and sin(ωt) represents quadrature modulation carrier signal.
3. The active stylus receiving circuit as claimed in claim 2 , wherein the digital signal obtained by sampling and converting the vector data signal through the analog-to-digital converter is: xi(n)×cos((2π×n×fin)/fs)+xq(n)×sin((2πn×fin)/fs), where fs is a sampling frequency of the analog-to-digital converter, and fin is a transmitting frequency at which the active stylus transmits the vector data signal.
4. The active stylus receiving circuit as claimed in claim 1 , wherein the demodulation circuit uses in-phase modulation carrier signal to perform demodulating operation on the interpolated digital signal to generate demodulated in-phase data, and uses quadrature modulation carrier signal to perform demodulating operation on the interpolated digital signal to generate demodulated quadrature data, so as to obtain the demodulated vector data represented by xi_rx+xq_rx, where xi_rx represents demodulated in-phase data, and xq_rx represents demodulated quadrature data.
5. A touch panel system, comprising:
an active stylus for transmitting vector data signal carrying vector data, wherein the vector data includes in-phase data and quadrature data;
a touch panel having a plurality of sensors for sensing the vector data signal transmitted by the active stylus; and
a receiving device having a plurality of active stylus receiving circuits, each active stylus receiving circuit corresponding to at least one sensor, and including:
an analog-to-digital converter for sampling and converting the vector data signal into digital signal having a plurality of sampling points;
an interpolation circuit for performing interpolating operation on the digital signal to increase a number of the sampling points representing the digital signal so as to generate interpolated digital signal; and
a demodulation circuit for performing demodulating operation on the interpolated digital signal to generate demodulated in-phase data and demodulated quadrature data, so as to obtain demodulated vector data, wherein the digital signal generated after the interpolation circuit performs interpolating operation is:
Y
(
m
)
=
{
X
(
n
)
+
X
(
n
+
1
)
2
,
m
=
2
,
4
,
6
→
∞
,
n
=
m
2
X
(
n
)
,
m
=
1
,
3
,
5
→
∞
,
n
=
floor
(
m
2
)
+
1
,
where Y( ) represents interpolated digital signal, X( ) represents digital signal outputted by the analog-to-digital converter, and floor( ) represents a floor function.
6. The touch panel system as described in claim 5 , wherein the vector data signal generated by the active stylus using carrier signal to modulate the vector data is: xi(t)cos(πωt)+xq(t)sin(ωt), where xi(t) represents in-phase data, xq(t) represents quadrature data, cos(ωt) represents in-phase modulation carrier signal, and sin(ωt) represents quadrature modulation carrier signal.
7. The touch panel system as claimed in claim 6 , wherein the digital signal obtained by sampling and converting the vector data signal through the analog-to-digital converter is: xi(n)×cos((2πn×fin)/fs)+xq(n)×sin((2πn×fin)/fs), where fs is a sampling frequency of the analog-to-digital converter, and fin is a transmitting frequency at which the active stylus transmits the vector data signal.
8. The touch panel system as claimed in claim 5 , wherein the demodulation circuit uses in-phase modulation carrier signal to perform demodulating operation on the interpolated digital signal to generate demodulated in-phase data, and uses quadrature modulation carrier signal to perform demodulating operation on the interpolated digital signal to generate demodulated quadrature data, so as to obtain the demodulated vector data represented by xi_rx+xq_rx, where xi_rx represents demodulated in-phase data, and xq_rx represents demodulated quadrature data.