Allwinner A20 - Principle of Operation

A20 User Manual (Revision 1.2) Copyright © 2013 Allwinner Technology Co., Ltd. All Rights Reserved. Page 201 / 812
X1-DATA
FS_TIME
Conversion Time
Y1-DATA
Single Touch No Pressure Measurement Mode
ADC-DATA
FS_TIME
Conversion Time
General ADC Mode
1.15.5. Principle of Operation
BASIC PRINCIPLE
The controller is a typical type of successive approximation ADC (SAR ADC), contains a sample/hold,
analog-to-digital conversion, serial data output functions. The analog inputs (X+,X-,Y+,Y-) via control
register enter the ADC, ADC can work in single-ended or differential mode. Selecting Aux ADC or
temperature should work in single-ended mode; as a touch screen application, it works in a
differential mode, which can effectively eliminate the impact on conversion accuracy caused by the
parasitic resistance of the driver switch and external interference.
SINGLE-ENDED MODE
When the TP controller is in the measurement mode of AUX or Temp, the internal ADC is in
single-ended mode, using the 3V reference source as the ADC reference voltage, application of the
principle of single-ended mode is shown below: