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OP220GP データシート(PDF) 8 Page - Analog Devices |
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OP220GP データシート(HTML) 8 Page - Analog Devices |
8 / 12 page REV. A OP220 –8– OP220 INPUT OUTPUT 100pF 25k 10 0% 100 90 2 s 20mV 50mV Figure 2. Small-Signal Transient Response 10 0% 100 90 5V 2V OP220 INPUT OUTPUT CL 100pF RL 25k 200 s 10k 40k Figure 3. Large-Signal Transient Response INSTRUMENTATION AMPLIFIER APPLICATIONS OF THE OP220 Two Op Amp Configuration The excellent input characteristics of the OP220 make it ideal for use in instrumentation amplifier configurations where low-level differential signals are to be amplified. The low-noise, low input offsets, low drift, and high gain combined with excellent CMRR provide the characteristics needed for high-performance instru- mentation amplifiers. In addition, the power supply current drain is very low. The circuit of Figure 4 is recommended for applications where the common-mode input range is relatively low and differential gain will be in the range of 10 to 1,000. This two op amp instrumen- tation amplifier features independent adjustment of common-mode rejection and differential gain. Input impedance is very high since both inputs are applied to noninverting op amp inputs. R4 R3 VO A2 A1 V1 + – VD VCM + 1/2 VD VCM – 1/2 VD R1 R2 1/2 OP220 1/2 OP220 GAIN ADJ R0 V R R R R R R RR R V R R R R R R V RR R R V R R V OD CM OD =+ + Ê ËÁ ˆ ¯˜ + + È Î Í ˘ ˚ ˙ +- Ê ËÁ ˆ ¯˜ == = = + Ê ËÁ ˆ ¯˜ 4 3 1 1 2 2 1 3 4 23 0 4 3 3 4 2 1 12 3 4 2 1 1 0 If then , Figure 4. Two Op Amp Instrumentation Amplifier Configuration The input voltages are represented as a common-mode input VCM plus a differential input VD. The ratio R3/R4 is made equal to the ratio R2/R, to reject the common-mode input VCM. The differential signal VD is then amplified according to: V R R R R RR R V R R R R O O D =+ + + Ê ËÁ ˆ ¯˜ = 4 3 1 3 4 23 3 4 2 1 , where Note that gain can be independently varied by adjusting RO. From considerations of dynamic range, resistor tempco match- ing, and matching of amplifier response, it is generally best to make RX, R2, R3, and R4 approximately equal. Designating R1, R2, R3, and R4 as RN allows the output equation to be further simplified: V R R VR R R R R O N O DN =+ Ê ËÁ ˆ ¯˜ == = = 21 1 2 3 4 , where Dynamic range is limited by A1 as well as A2; the output of A1 is: V R R VV N O DCM 11 2 =- + Ê ËÁ ˆ ¯˜ + If the instrumentation amplifier were designed for a gain of 10 and maximum VD of ±1 V, then RN/RO would need to be four and VO would be a maximum of ±10 V. Amplifier A1 would have a maximum output of ±5 V plus 2 VCM, thus a limit of ±10 V on the output of A1 would imply a limit of ±2.5 V on VCM. A nominal value of 100 k W for RN is suitable for most applica- tions. A range of 200 W to 25 kW for RO will then provide a gain range of 10 to 1,000. The current through RO is VD/RO, so the amplifiers must supply ±10 mV/200 W when the gain is at the maximum value of 1,000 and VD is at ±10 mV. Rejecting common-mode inputs is most important in accurately amplifying low-level differential signals. Two factors determine the CMR of this instrumentation amplifier configuration (assuming infinite gain): 1. CMRR of the op amps 2. Matching of the resistor network (R3/R4 = R2/R1) |
同様の部品番号 - OP220GP |
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同様の説明 - OP220GP |
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