Amplifiers are used in a wide variety of applications, some are general-purpose and suitable for most applications, while some Operational Amplifiers are designed for higher levels of performance in specific areas. For some applications that require enhanced performance, choosing the right op amp will give you the best performance your design requires.
Power
The first thing to notice is that there is no "ground" pin on the op amp. Op amps can all be powered from a single supply, but some require positive and negative supplies. It is important to note that when selecting an amplifier, you need to be mindful of performance problems that may arise from operating at low voltages. In portable systems, amplifiers are required to operate at very low supply voltages, and supply currents should be small to prolong battery life. In addition, these amplifiers need to have good output drive capability and high open-loop gain.
For low-power op amps, the supply current has a wide variation range when the output voltage changes. At low supply voltages, the output current drive capability may also drop significantly. Therefore, it is necessary to consult the parameter table to determine the output current drive capability that can be achieved at a specific supply voltage.
Operational Amplifiers
The Power Supply Rejection Ratio (PSRR) determines how sensitive the op-amp is to changes in the power supply. You don't want power supply noise (from AC power) or drift (from the battery) to affect the output. The specification is listed as a decibel (dB) value, where every 20 dB increase is a 10-fold increase in the ratio. So the 60 dB value here means that a 1-volt change in the power supply will cause a 0.001 volt (or 1 millivolt) change in the output.
This value depends on the actual supply voltage and the frequency of the noise. Higher operating voltages and lower noise frequencies generally yield better PSRR figures. Often, datasheets provide graphs that show these changes.
If you're using an op amp with digital logic (which often results in a lot of power supply noise), you'll want an op amp with a good PSRR rating. If your op amp is an all-analog design with a good, regulated analog supply, this parameter may not be important.
The current required to power the amplifier is defined as the supply current (Is). This is quiescent current. This does not include external components or any output current. If there are multiple amplifiers in a single package, this usually refers to a single amplifier. However, the datasheet specifies this. Obviously, a battery-powered circuit will work longer with an amplifier that consumes less power. Sometimes this is listed in milliwatts (or microwatts) as power consumption (Pd). Therefore, you must convert it to mA (or µA) using the supply voltages listed in the table.
Selection Indicators
1. Input offset voltage
When the op amp is used in open loop, the DC voltage applied between the two input terminals makes the DC output voltage of the amplifier zero. An amplifier whose Vos is much smaller than the measured DC quantity can be selected. If you only care about the AC component in the signal under test, you can add AC coupling circuits at the input and output to eliminate it.
2. Offset voltage drift
The input offset voltage changes when independent variables such as temperature change, time duration, and supply voltage change. Op amps with high stability can be selected. Some op amps have auto-zeroing technology, which continuously measures the offset and subtracts the current offset voltage during signal processing.
3. Bias Voltage and Input Bias Current
In precision circuit design, the bias voltage is a critical factor. An accurate amplifier requires a bias voltage drift of less than 200µV and an input voltage noise of less than 6nV/√Hz. Bias voltage drifts over temperature is required to be less than 1μV/°C.
Amplified bias voltages can cause large output voltages and can account for a large portion of the output swing. Temperature sensing and tension measurement circuits are examples of applications that utilize precision amplifiers.
The input bias current refers to the average value of the current flowing into the two input terminals when the output is maintained at the specified level Ib=(Ib1+Ib2)/2. Its range is 60fA to 100µA.
A low input bias current is sometimes required. The amplifier in the optical receiver must have low bias voltage and low input bias current.
Of all amplifiers, the chopper amplifier provides the lowest bias voltage and lowest bias voltage drift over temperature. Many weight measurement devices have high requirements for gain and need to configure high-quality precision amplifiers. At this time, chopper amplifiers are a good choice.
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Package types, including dual-in-line through-hole mount and surface mount, also need to be considered when selecting an op amp. Packages that contain multiple op amps can be selected. Space and cost on the circuit board can be saved.