If you use an op amp and an IC difference amplifier, no user supplied precision resistors or resistor adjustments are required. Furthermore, certain applications using high voltage and high current op amps can derive important benefits from single supply operation. Feedback dictates the performance of an op amp both in function and in quality. Dual and quad designs feature completely independent circuitry for lowest crosstalk and freedom from interaction. Single, dual, and quad versions have identical specifications for design flexibility. The OPA series operates on a single supply as low as 2.
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OPA series op amps are laser-trimmed to the reduce offset voltage difference between the N-channel and P-channel input stages, resulting in improved common- mode rejection and a smooth transition between the N-channel pair and the P-channel pair. A double-folded cascode adds the signal from the two input pairs and presents a differential signal to the class AB output stage.
Normally, input bias current is approximately fA, however, input voltages exceeding the power supplies by more than mV can cause excessive current to flow in or out of the input pins. Momentary voltages greater than mV beyond the power supply can be tolerated if the current on the input pins is limited to 10mA. This is easily accomplished with an input resistor as shown in Figure 3. Many input signals are inherently current-limited to less than 10mA, therefore, a limiting resistor is not required.
However, all op amps under certain conditions may become unstable. Op amp configuration, gain, and load value are just a few of the factors to consider when determin- ing stability. An op amp in unity gain configuration is the most susceptible to the effects of capacitive load.
In unity gain, OPA series op amps perform well, with a pure capacitive load up to approximately pF. This significantly reduces ringing with large capacitive loads. However, if there is a resistive load in parallel with the capacitive load, it creates a voltage divider introducing a dc error at the output and slightly reduces output swing. This error may be insignificant. However, they also offer excellent performance for higher speed converters.
When used with the minia- ture package options of the OPA series, the combina- tion is ideal for space-limited and low power applications. For further information consult the ADS data sheet. In the inverting configuration, filtering may be accomplished with a ca- pacitor across the feedback resistor Figure 6.