section 3 HIGH RESOLUTION SIGNAL CONDITIONING ADCS Walt Kester, James Bryant, Joe Buxton The trend in ADCs and dACs is toward higher speeds and higher resolutions at reduced power levels. Modern data converters generally operate on + oV(dua single +3V supply This trend has created a number of design and app licationg supply)or +5V(single supply). There are now a few converters which operate or problems which were much less important in earlier data converters, where+15V supplies were the standard Lower supply voltages imply smaller input voltage ranges, and hence more susceptibility to noise from all potential sources: power supplies, references, digital signals, EMI/RFI, and probably most important, improper layout, grounding, and decoupling techniques. Single-supply adCs often have an input range which is not referenced to ground. Finding compatible single-supply drive amplifiers and dealing with level shifting of the input signal in direct-coupled applications also becomes a challenge In spite of these issues, components are now available which allow extremely high resolutions at low supply voltages and low power. This section discusses the applications problems associated with such components and shows techniques for successfully designing them into systems LOW POWER LOW VOLTAGE ADC DESIGN ISSUES Low Power ADCs ty pically run on #5V, +5V, +5/+3v, or+3v Lower Signal Swings Increase Sensitivity to All Types of Noise (Device, Power Supply, Logic, etc. Device Noise Increases at low quiescent currents Bandwidth Suffers as Supply Current Drops Input Common-Mode Range May be Limited Selection of Zero-Volt Input/output Amplifiers is Limited Auto-Calibration Modes Highly Desirable at High Resolutions Figure 3.12 SECTION 3 HIGH RESOLUTION SIGNAL CONDITIONING ADCs Walt Kester, James Bryant, Joe Buxton The trend in ADCs and DACs is toward higher speeds and higher resolutions at reduced power levels. Modern data converters generally operate on ±5V (dual supply) or +5V (single supply). There are now a few converters which operate on a single +3V supply. This trend has created a number of design and applications problems which were much less important in earlier data converters, where ±15V supplies were the standard. Lower supply voltages imply smaller input voltage ranges, and hence more susceptibility to noise from all potential sources: power supplies, references, digital signals, EMI/RFI, and probably most important, improper layout, grounding, and decoupling techniques. Single-supply ADCs often have an input range which is not referenced to ground. Finding compatible single-supply drive amplifiers and dealing with level shifting of the input signal in direct-coupled applications also becomes a challenge. In spite of these issues, components are now available which allow extremely high resolutions at low supply voltages and low power. This section discusses the applications problems associated with such components and shows techniques for successfully designing them into systems. LOW POWER, LOW VOLTAGE ADC DESIGN ISSUES Low Power ADCs typically run on 5V, +5V, +5/+3V, or +3V Lower Signal Swings Increase Sensitivity to All Types of Noise (Device, Power Supply, Logic, etc.) Device Noise Increases at Low Quiescent Currents Bandwidth Suffers as Supply Current Drops Input Common-Mode Range May be Limited Selection of Zero-Volt Input/Output Amplifiers is Limited Auto-Calibration Modes Highly Desirable at High Resolutions Figure 3.1