数模混合电路策画中信号串扰控制.pdfVIP

AN2010 APPLICATION NOTE Interference Control during Mixed-Signal (Analog and Digital) Board Design In a mixed-signal circuit, using both analog and digital components, the fast speed digital circuit section is always a potential source of noise, especially for the sensitive analog circuit section. The typical CMOS digital device has a very low quiescent current, but study shows that simultaneous switching noise (SSN, also known as ground bounce), caused by CMOS circuit switching current, forms the major contribution to the overall circuit noise. This application note describes how to deal with these problems, using an Analog-to-Digital converter as an example. The 90C7101 ADC Verification board is an internal verification tool, used by ST, and is not publicly available. However, it is used here as an illustrative example, since the PCB design rules are ap- plicable to any board design. The 90C7101 Turbo-Lite microcontroller is a mixed-signal SOC chip that incorporates an Analog-to-Digital Converter (ADC), an 8-bit microcontroller, and various peripherals. The on-chip converter consists of an 8-input analog multiplexer, and a 10-bit binary successive approximation ADC. To achieve the 10-bit res- olution, special attention should be paid to minimize the interference between digital and analog circuits. Figure 1. 90C7101 ADC Block Diagram AVREF VREF ADC0 P1.0 ADC1 P1.1 ADC2 P1.2 ADC3 P1.3 ADC4 Analog 10-Bit SAR ADC P1.4 MUX ADC5 P1.5 ADC6 P1.6