Author: TakashiM_61 Version: **
What is the hardware consideration to use ADC in FM4 device?
In order to use ADC properly, the reference voltage (Analog Voltage Reference High (AVRH) /Analog Voltage Reference Low (AVRL)) are important. It is necessary to suppress the reference voltage swing and avoid noise on power and ground lines as much as possible.
From schematic/circuit observation, the following points must be considered:
- AVRH / AVRL
- AVRH-C Bypass capacitor “0.1 μF” is connected between AVRH and AVRL lines.
- AVRH-R Register “3.3Ω” is populated on AVRH line. This is to make high frequency noise flows in the route of by AVRH-C Bypass capacitor.
- AVCC / AVSS
- AVCC-C Bypass capacitor “0.1 μF” is connected between AVCC and AVSS lines.
- AVCC-R Register “10Ω ” is populated on AVCC line. This is to make high frequency noise flows in the route of by AVCC-C Bypass capacitor.
From Layout observation, AVRH-R, AVRH-C, AVCC-R and AVCC-C should be populated close to each pin without any vias to avoid redundant line length between the pin and register/capacitor:
- AVRH pin to AVRH-R
- AVRH pin to AVRH-C
- AVRL pin to AVRH-C
- AVSS pin to AVCC-C
- AVCC pin to AVCC-C
The line between the AVRL pin to AVRH-C should be separated from the line between AVSS pin and AVSS-C to avoid common impedance.