A programmable operational amplifier is an operational amplifier (OU), all of which internal rest currents are set by means of an external current supplied to a special OU terminal . In other words, the external current "programs" the value of the current consumed by the operational amplifier.
Content
Assignment
Programming is necessary in order to achieve optimal for the given scheme parameters of the OS for speed and current consumption. The choice of the quiescent current value is the achievement of a compromise between economy and speed:
- At low current currents, an op-amp consumes a small current for its own power, however, the response of an op-amp (the slew rate of the output voltage and the product of the gain by the bandwidth) is low.
- At high quiescent currents, good speed is achieved, but the current consumption increases.
Quiescent Control
The rest current of an opamp is controlled through a special output. Depending on the type of OS, one of the following methods is used:
- The consumed current is a specified number of times the current supplied to the control terminal. The control current is supplied by connecting a high-resistance resistor between the positive power bus and the control terminal. For example, for CA3078 [1] with a control current of 2 μA, the current consumed is 20 μA. When the supply voltage changes, the control current, and hence the consumption, will change.
- Current consumption is selected from several predefined options. For example, for the TLC251 op amp [2], the current consumption can be set at 10 μA, 150 μA or 1 mA [1] . The advantage of this method is that the installed current is weakly dependent on the supply voltage.
Using programmable op amps in circuitry
Programmable opamps are used in electronic circuits, which are subject to severe restrictions on current consumption, for example, circuits powered by galvanic cells , batteries , solar batteries , and also with parasitic power.
Notes
- ↑ For this type of op amp, a current of 10 µA is achieved by connecting a control output to a positive power bus, 1 mA to a negative bus, and 150 µA when a medium voltage is applied to the control terminal (see documentation).
Literature
- Horowitz P., Hill U. The Art of Circuit Engineering : In 3 volumes: T. 1. Trans. from English. - 4th ed., pererab. and additional - Moscow: Mir, 1993. — 413 s., ill. ISBN 5-03-002337-2 .