Question: What is the RefMux setting and what is the AGndBypass option in PSoC® Designer™? What is their significance?
RefMux setting: This parameter enables the user to select the analog ground and the input range of the analog blocks. See Figure 1.
The reference generator generates three voltages: AGND (the analog ground for all the analog blocks), RefHi, and RefLo (which sets the range for the analog resources). These voltages are derived from VDD, a 1.3 V bandgap reference generator, or external voltages connected to P2 and P2. For example, if VDD = 5.0 V and the RefMux is set to VDD/2 ± BandGap, this sets AGND to 2.5 V, RefHi to 3.8 V, and RefLo to 1.2 V. This means that the allowed input range for the analog resources is from 1.2 V to 3.8 V.
Figure 1. Analog Ground Bypass
For detailed information about the RefMux setting, see AN2219 - PSoC® 1 Selecting Analog Ground and Reference and Chapter 21- Analog Reference in the PSoC Technical Reference Manual.
AGndBypass option: When AGND Bypass is set to Enabled, pin P2 is in High-Z Analog mode. An external capacitor connected between P2 and VSS reduces the noise at the AGND input. Typical values for the bypass capacitor are 0.01 µF and should not exceed 0.1 µF.