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The information presented in this cross reference is based on TOSHIBA's selection criteria and should be treated as a suggestion only. Please carefully review the latest versions of all relevant information on the TOSHIBA products, including without limitation data sheets and validate all operating parameters of the TOSHIBA products to ensure that the suggested TOSHIBA products are truly compatible with your design and application.
Please note that this cross reference is based on TOSHIBA's estimate of compatibility with other manufacturers' products, based on other manufacturers' published data, at the time the data was collected.
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Typical op-amps have an open-loop gain on the order of 105 (100 dB). Without feedback, op-amps make circuit design difficult because of high gain sensitivity. Negative feedback makes it possible to set the gain and cut-off frequency to the desired values, thereby improving their stability and reducing performance variation, part-to-part variation, and sensitivity to temperature and other environmental parameters.
Figure 1 shows an inverting amplifier. The closed-loop gain (Gv) of this negative feedback circuit can be simply expressed as:
Gv = -R2/R1
This equation indicates that the closed-loop gain is solely determined by the ratio of external resistor values and is not affected by environmental factors.
Figure 2 shows the Bode plot of a typical op-amp. The open-loop gain, i.e., the gain without negative feedback, decreases at a rate of 6 dB/oct (= 20 dB/dec). In contrast, the closed loop gain has a constant gain from DC to 10 kHz in this figure (which depends on the frequency response of the op-amp). As indicated by this example, using feedback provides an amplifier with bandwidth.