wm9705seft-v Wolfson Microelectronics plc, wm9705seft-v Datasheet - Page 40

• Manufacturer Part Number: wm9705seft-v
• Description: Multimedia Ac?97 Codec With Integrated Touch Screen Controller
• Manufacturer: Wolfson Microelectronics plc

WM9705
PEN DIGITISER OPERATION
Figure 18 Pen Digitiser Block Diagram
w
X-
Figure 19 Y Position Conversion
Yswp
Yswn
Y-
Y+
Rpen
Rscry
Y-
Y+
The pen digitiser function comprises a 12 bit successive approximation ADC, with a multi-channel
input multiplexor to select which signal to convert, and a switching matrix to control driving of
signals to the resistive touchscreen plates. A finite state machine is provided in order to control
and sequence conversion operations.
A pen-down detection scheme is provided to allow detection of when the pen is in contact with the
screen. This allows for the touchscreen to only be driven whilst the pen is down, saving on
unnecessary power consumption. This minimises any degradation in audio performance that may
occur due to the significant currents that flow through the on-chip screen drive switches. Figure 18
shows symbolically these component elements and their connectivity.
Rpen
Rpu
Rscrx
X+
X-
X+
Vrswyp
Vrswyn
MXxp
MXxn
PCBEEP
AUXADC
PHONE
PDRES
BMON
Y+
X+
Y-
X-
converter
A/D
Yswp
Yswn
Xswp
Xswn
AUX
input
MUX
Rpusw
Prsw
Ipress
Pressure switch
X+
Xswp
X-
Xswn
Figure 20 X Position Conversion
ADC ip Mux
Rpen
Vref+ switches
Vref- switches
MXaux
MXyp
MXxp
MXyn
MXxn
Vrswap
Vrswyp
Vrswxp
Vrswxn
Vrswyn
Vrswan
Switch control
comparator
Pen detect
12 bit
SAR
ADC
Y-
Y+
Pen Controller
State machine
Vref+
Vref-
and AC link
interface
Vrswxp
Vrswxn
MXyp
MXyn
PD Rev 4.5 July 2008
ADC control
12 bit op
Production Data
converter
A/D
PENDET
MASK
BUSY
40