触屏技术介绍.ppt

Capacitive Sensing Technology Overview 2 PSoC = P rogrammable S ystem o n C hip Features: ? Configurable Analog Blocks ? ADCs, DACs , filters, amplifiers, comparators, modulators etc. ? Configurable Digital Blocks ? Timers, Counters, PWMs , UART, SPI, SPI, I2C, IrDA, etc. ? 4KB to 32KB of Flash for code store ? Emulate EEPROM in Flash ? 256B to 2KB of SRAM for data store ? M8C Microcontroller ? Same core used in Cypress USB What Is PSoC? You Build the Device YOU Need! 3 CapSense : Theory ?C P is sum of sensor pad capacitance and parasitics .?C P is higher when finger is on the sensor pad. ? Parasitic Capacitance is generated by coupling from the sensor pad to traces, ground plane, and any surrounding conductive material. ? Design challenge is to find a small C F (-) in the presence of a large C P (10-30pF) C PC PC fC f 4 CSR : C ap S ense with R elaxation Oscillator 16-bit Timer V REF Data Processing C X EN Oscillator SW 1 8-bit PWM EN no finger finger 5 Key Concept: Switched Capacitor = A Resistor V1 V2 I Resistor : I=(V1-V2)/R (if V1>V2) V1 V2 S1 S2 Switched Capacitor : Phase 1: S1=CLOSED, S2=OPEN Q1=C * V1 Phase 2: S1=OPEN, S2=CLOSED Q2=C * V2 ? Q = Q1-Q2 = C * V1-C * V2 = C(V1-V2) I= ? Q / ? t -or- I= ? Q * fsw I=C(V1-V2) * fsw RC 6 Resistor : I=(V1-V2)/R Switched Capacitor : I=C(V1-V2) * fsw Equivalent Resistor : (V1-V2)/R = C(V1-V2) * fsw 1/R = C * fsw R=1/ C * fsw The equivalent resistance of each sensor can be controlled by the switching frequency Key Concept: Switched Capacitor = A Resistor 7 CSD : Overview of circuitry 8 CSD : Switched capacitor input ? Sensing switching capacitor Cx is ? Charged to the voltage source Vdd at phase Phi 1 clock signal; ? Discharged to the voltage V cfilt at phase Phi 2 clock signal; ? The switching capacitor is equivalent to a resistor with value R c1 c s s R f C ? 9 CSD : Delta-sigma modulator ? The sigma-delta modulator is formed by the comparator, parator