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OP221GZ bảng dữ liệu(PDF) 9 Page - Analog Devices |
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OP221GZ bảng dữ liệu(HTML) 9 Page - Analog Devices |
9 / 12 page REV. C OP221 –9– SPECIAL NOTES ON THE APPLICATION OF DUAL MATCHED OPERATIONAL AMPLIFIERS Advantages of Dual Monolithic Operational Amplifiers Dual matched operational amplifiers provide the engineer with a powerful tool for designing instrumentation amplifiers and many other differential-input circuits. These designs are based on the principle that careful matching between two operational amplifiers can minimize the effect of dc errors in the individual amplifiers. Reference to the circuit shown in Figure 6, a differential-in, differential-out amplifier, shows how the reductions in error can be accomplished. Assuming the resistors used are ideally matched, the gain of each side will be identical. If the offset voltages of each amplifier are perfectly matched, then the net differential voltage at the amplifier’s output will be zero. Note that the output offset error of this amplifier is not a function of the offset voltage of the individual amplifiers, but only a function of the difference (degree of matching) between the amplifiers’ offset voltages. This error-cancellation principle holds for a considerable number of input referred error parameters—offset voltage, offset voltage drift, inverting and noninverting bias currents, common mode and power supply rejection ratios. Note also that the impedances of each input, both common-mode and differential-mode, are high and tightly matched, an important feature not practical with single operation amplifier circuits. INPUT OUTPUT SIDE ‘A’ SIDE ‘R’ R1 R2 R3 R4 OP221 + – + – Figure 6. Differential-In, Differential-Out Amplifier INSTRUMENTATION AMPLIFIER APPLICATIONS Two-Op Amp Configuration The two-op amp circuit (Figure 7) is recommended where the common-mode input voltage range is relatively limited; the common-mode and differential voltage both appear at V1. The high open-loop gain of the OP221 is very important in achieving good CMRR in this configuration. Finite open-loop gain of A1 (Ao1) causes undesired feedthrough of the common-mode input. For Ad/Ao, << 1, the common-mode error (CME) at the out- put due to this effect is approximately (2 Ad/Ao1) x VCM. This circuit features independent adjustment of CMRR and differ- ential gain. Three-Op Amp Configuration The three-op amp circuit (Figure 8) has increased common- mode voltage range because the common-mode voltage is not amplified as it is in Figure 7. The CMR of this amplifier is directly proportional to the match of the CMR of the input op amps. CMRR can be raised even further by trimming the output stage resistors. R1 R2 GAIN ADJ R0 V1 R3 A1 A2 1/2 OP221 1/2 OP221 VCM – 1/2VD VCM + 1/2VD AD = 2 1+ R1 R0 R4 VO – ADVD VO = 1 + 1 2 R2 R1 + R2 + R3 R0 + Vd + – VCM R3 R4 R4 R3 R4 R3 R3 R4 R2 R1 IF R1 = R2 = R3 = R4, THEN VO = 2 1 + VD R1 R0 Vd – + Figure 7. Two-Op Amp Circuit A1 A2 R1 R2 R0 1/2 OP221 VCM – 1/2VD VO = 2 1 + VD 2R1 R0 A3 1/2 OP221 OP221 R2 R2 VCM + 1/2VD V– – – V+ Vd V+ V– R2 VO R1 V2 V1 Figure 8. Three-Op Amp Circuit |
Số phần tương tự - OP221GZ |
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Mô tả tương tự - OP221GZ |
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