晶闸管电源

Amplifiers: Op Amps

Texas Instruments Incorporated

Figure 11 shows the frequency responsesof several of these chips. Figure 12 showsthe results of using various ferrite chipsfrom the same AG family.

As expected, all of these graphs showthe same type of results obtained withthe noninverting configuration. Using alow-Q ferrite chip with high impedancewill result in a stable system. Although thenoise plots for this configuration are notpresented here, they will show the sametype of results as the noninverting configu-ration; using ferrite chips will have thelowest output noise of any configuration.

Conclusion

Although this article shows only two con-figurations with capacitors in the feedbackpath, it shows the fundamental feasibilityof this compensation technique. Whileresistors do work very well, producing themost stable responses, the drawbacks ofthe output noise coupled with the dc andac errors may limit some of the ing ferrite chips helps alleviate manyof these issues, producing the lowest noiseof all with no dc errors or in-band ac sig-nal errors; and stability is almost as goodas when utilizing resistors. It is importantto choose the proper ferrite chip with theamplifier; but this is considered normalprocedure for any circuit design and is nomore difficult than selecting the rightamplifier for the system.

This simple technique helps eliminateone of the major drawbacks of using theCFB amplifier while allowing any systemto enjoy many of its benefits. Designers ofmultiple feedback filters, for example, oncelimited to the use of VFB amplifiers, cannow take advantage of the superior slewrates and lack of gain-bandwidth productcharacteristics found in the CFB amplifier.

References

For more information related to this article,you can downloadan Acrobat Reader fileat /sc/techlit/litnumberandreplace “litnumber”with the TI Lit. #for the materials listed below.

Document TitleTI Lit. #1.“Voltage Feedback Vs. Current Feedback

Op Amps,” Application Report . . . . . . . . . . . . . .slva0512.“The Current-Feedback Op Amp: A High-Speed Building Block,” Application Bulletin . . .sboa0763.“Current Feedback Amplifiers: Review, Stability Analysis, and Applications,”

Application Bulletin . . . . . . . . . . . . . . . . . . . . . . .sboa0814.“Low-Noise, High-Speed Current Feedback

Amplifiers,” Data Sheet . . . . . . . . . . . . . . . . . . . .slos3855.“Effect of Parasitic Capacitance in Op Amp

Circuits,” Application Report . . . . . . . . . . . . . . .sloa013

Related Web sites

/sc/device/partnumber

Replace partnumberwith OPA685, THS3112, THS3202orTHS4012