This preview shows page 1. Sign up to view the full content.
Unformatted text preview: 3
RG7 ADC.21 ADC The configuration … ADC.22 ADC.23 ADC Register (SFR) settings ADC.24 ADC Register (SFR) settings ADC.25 Digital input:
input as we used
it before!! ADC.26 ADC The result … ADC.27 ADC The result … ADC.28 ADC Outside & Inside ADC.29 ADC Timing … ADC.30 Sample/Hold Acquisition Time
Tacq = Amplifier Settling Time (Tamp)
+ Holding Capacitor Charging Time (Tc)
+ Temperature Coefficient Time (Tcoff) Tacq = Tamp + Tc + Tcoff
Tamp = 2 µs for PIC 16F877 Next few slides find Tc & Tcoff:
ADC.31 Calculations for Tc:
Capacitor Charges through Series Resistances:
Rs = External signals source resistance (use 10,000 in lab)
Ric = Interconnect Resistance (Ric ≤ 1,000 ohm)
Rss = Sample Switch Resistance (function of Vdd)
(for Vdd = 5v, Rss = 7,000 ohm) CHOLD = Capacitor = 120 * 10-12 farads So Time for capacitor to charge:
Tc = - CHOLD*( Rs + Ric + Rss) * ln (1/2047)
ADC.32 Calculations for Tc (continued):
Tc = - CHOLD( Rs + Ric + Rss) * ln (1/2047)...
View Full Document
This document was uploaded on 01/22/2014.
- Fall '14