Figure 2-1 shows the power-supply connections, reference connections, and the associated decoupling filter capacitors for the ADS8900. The reference filter comprised of C12 and R16 is at the reference buffer output and must be as close as possible to the ADC reference pin (pin 7). This figure also shows the analog input connections, but the driver amplifier is in Figure 2-2. The digital signal connections are shown on the right hand side of Figure 2-1. The connector J4 is a test point header that can be used to monitor digital signals. Also, J4 can be used to apply digital signals in cases where the included PHI controller is not used. Each digital signal has a series 0-Ω resistor. This resistor can be changed to a 50-Ω resistor to provide signal conditioning for noisy digital signals. The included PHI controller digital signals do not require this conditioning so the default value is 0 Ω. Figure 2-1 also shows the PHI connector, J1. This connector provides the SPI digital signals, power supplies, and I²C communications for the EVM.