WM9705 datasheet(40/55 Pages) WOLFSON

номер детали	WM9705

подробное описание детали	Multimedia AC97 CODEC with Integrated Touch Screen Controller

PDF	55 Pages

Scroll/Zoom	100%

производитель	WOLFSON [Wolfson Microelectronics plc]

домашняя страница	http://www.wolfsonmicro.com

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40 / 55 page

WM9705

Production Data

PD Rev 4.0 December 2003

PEN DIGITISER OPERATION

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.

ADC ip Mux

Rscrx

Rscry

Rpen

Y+

Y-

X+

X-

12 bit

SAR

ADC

Vref+

Vref-

Y+

X+

Y-

X-

PHONE

PCBEEP

AUXADC

BMON

AUX

input

MUX

PDRES

PENDET

BUSY

12 bit op

Rpusw

Xswp

Xswn

Yswn

Pressure switch

Rpu

Pen Controller

State machine

and AC link

interface

MASK

Switch control

ADC control

Pen detect

comparator

Vref+ switches

Vref- switches

Ipress

Yswp

Vrswap

Vrswyp

Vrswxp

Vrswxn

Vrswyn

Vrswan

MXxp

MXyn

MXxn

MXaux

MXyp

Prsw

Figure 18 Pen Digitiser Block Diagram

Y+

X+

X-

Y-

Rpen

A/D

converter

Vrswyn

Vrswyp

Yswn

Yswp

MXxp

MXxn

Figure 19 Y Position Conversion

Y+

X+

X-

Y-

Rpen

A/D

converter

Vrswxn

Vrswxp

Xswn

Xswp

MXyp

MXyn

Figure 20 X Position Conversion

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