SECTION 1 SINGLE-SUPPLY AMPLIFIERS Adolfo garcia Over the last several years, single-supply operation has become an increasingly important requirement as systems get smaller, cheaper, and more portable nd total circuit consumption is an important and often dominant design issue, and in some instances, more important than cost. This makes low-voltage/low supply current operation critical; at the same time, however, accuracy and precision requirements have forced IC manufacturers to meet the challenge of" doing more with less"in their amplifier design SINGLE-SUPPLY AMPLIFIERS ■ Single Supply Offers Lower Power Battery Operated Portable Equipment Simplifies Power Supply Requirements ■ But Watch out for: Signal-swings limited, therefore more sensitive to errors caused by offset voltage, bias current, finite open-loop gain, noise, etc. o More likely to have noisy power supply because of sharing with digital circuits DC coupled, multi-stage single-supply circuits can get very tricky! Rail-to-rail op amps needed to maximize signal swIngs In a single-supply application, the most immediate effect on the performance of an amplifier is the reduced input and output signal range. As a result of these lower input and output signal excursions, amplifier circuits become more sensitive to internal and external error sources. Precision amplifier offset voltages on the order of 0. 1mv are less than a 0.04 LSB error source in a 12-bit, 10v full-scale system. In a single-supply system, however, a"rail-to-rail "precision amplifier with an offset voltage of Imv represents a 0. 8LSB error in a 5V FS system, and 1.6LSB error in a 2.5V FS system Furthermore, amplifier bias currents, now flowing in larger source resistances to keep current drain from the battery low, can generate offset errors equal to or greater than the amplifiers own offset voltage Gain accuracy in some low voltage single-supply devices is also reduced, so device millions typically operate on dual supplies: for example, the OP07 family typee the selection needs careful consideration. Many amplifiers having open- loop gain However, many single-supply/rail-to-rail amplifiers for precision application2 SECTION 1 SINGLE-SUPPLY AMPLIFIERS Adolfo Garcia Over the last several years, single-supply operation has become an increasingly important requirement as systems get smaller, cheaper, and more portable. Portable systems rely on batteries, and total circuit power consumption is an important and often dominant design issue, and in some instances, more important than cost. This makes low-voltage/low supply current operation critical; at the same time, however, accuracy and precision requirements have forced IC manufacturers to meet the challenge of “doing more with less” in their amplifier designs. SINGLE-SUPPLY AMPLIFIERS Single Supply Offers: Lower Power Battery Operated Portable Equipment Simplifies Power Supply Requirements But Watch Out for: Signal-swings limited, therefore more sensitive to errors caused by offset voltage, bias current, finite open-loop gain, noise, etc. More likely to have noisy power supply because of sharing with digital circuits DC coupled, multi-stage single-supply circuits can get very tricky! Rail-to-rail op amps needed to maximize signal swings In a single-supply application, the most immediate effect on the performance of an amplifier is the reduced input and output signal range. As a result of these lower input and output signal excursions, amplifier circuits become more sensitive to internal and external error sources. Precision amplifier offset voltages on the order of 0.1mV are less than a 0.04 LSB error source in a 12-bit, 10V full-scale system. In a single-supply system, however, a "rail-to-rail" precision amplifier with an offset voltage of 1mV represents a 0.8LSB error in a 5V FS system, and 1.6LSB error in a 2.5V FS system. Furthermore, amplifier bias currents, now flowing in larger source resistances to keep current drain from the battery low, can generate offset errors equal to or greater than the amplifier’s own offset voltage. Gain accuracy in some low voltage single-supply devices is also reduced, so device selection needs careful consideration. Many amplifiers having open-loop gains in the millions typically operate on dual supplies: for example, the OP07 family types. However, many single-supply/rail-to-rail amplifiers for precision applications