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LB-9 Datasheet(PDF) 1 Page - National Semiconductor (TI) |
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LB-9 Datasheet(HTML) 1 Page - National Semiconductor (TI) |
1 / 3 page Universal Balancing Techniques IC op amps are widely accepted as a universal analog component. Although the circuit designs may vary, most devices are functionally interchangeable. However, offset voltage balancing remains a personality trait of the particular amplifier design. The techniques shown here allow offset voltage balancing without regard to the internal circuitry of the amplifier. The circuit shown in Figure 1 is used to balance out the offset voltage of inverting amplifiers having a source resis- tance of 10 k Ω or less. A small current is injected into the summing node of the amplifier through R 1. Since R1 is 2000 times as large as the source resistance the voltage at the arm of the pot is attenuated by a factor of 2000 at the summing node. With the values given and ±15V supplies the output may be zeroed for offset voltages up to ±7.5 mW. If the value of the source resistance is much larger than 10 k Ω, the resistance needed for R 1 becomes too large. In this case it is much easier to balance out the offset by supplying a small voltage at the non-inverting input of the amplifier. Figure 2 shows such a scheme. Resistors R 1 and R2 divide the voltage at the arm of the pot to supply a ±7.5 mW adjustment range with ±15V supplies. This adjustment method is also useful when the feedback element is a capacitor or non-linear device. This technique of supplying a small voltage effectively in series with the input is also used for adjusting non-inverting amplifiers. As is shown in Figure 3, divider R 1,R2 reduces the voltage at the arm of the pot to ±7.5 mW for offset adjustment. Since R 2 appears in series with R4,R2 should be considered when calculating the gain. If R 4 is greater than 10 k Ω the error due to R 2 is less than 1%. 00846001 R1 = 2000 R3 \ R4 R4 \ R3 ≤ 10 kΩ FIGURE 1. Offset Voltage Adjustment for Inverting Amplifiers Using 10 k Ω Source Resistance or Less 00846002 FIGURE 2. Offset Voltage Adjustment for Inverting Amplifiers Using Any Type of Feedback Element National Semiconductor Linear Brief 9 August 1969 © 2002 National Semiconductor Corporation AN008460 www.national.com |
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