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OP227GY Fiches technique(PDF) 10 Page - Analog Devices |
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OP227GY Fiches technique(HTML) 10 Page - Analog Devices |
10 / 16 page REV. A OP227 –10– BASIC CONNECTIONS OUT (A) V–(A) V–(B) OUT (B) (–) (+) (+) (–) 3 4 11 10 98 7 21 14 13 12 5 6 10k 10k V+(A) V+(A) INPUTS INPUTS A B OP227 Figure 1. Offset Nulling Circuit APPLICATIONS INFORMATION Noise Measurements To measure the 80 nV peak-to-peak noise specification of the OP227 in the 0.1 Hz to 10 Hz range, the following precautions must be observed: •The device must be warmed up for at least five minutes. As shown in the warm-up drift curve, the offset voltage typically changes 4 mV due to increasing chip temperature after power-up. In the 10-second measurement interval, these temperature- induced effects can exceed tens-of-nanovolts. ∑ For similar reasons, the device must be well shielded from air currents. Shielding minimizes thermocouple effects. ∑ Sudden motion in the vicinity of the device can also “feed- through” to increase the observed noise. ∑ The test time to measure 0.1 Hz to 10 Hz noise should not exceed 10-seconds. As shown in the noise-tester frequency- response curve, the 0.1 Hz corner is defined by only one zero to eliminate noise contributions from the frequency band below 0.1 Hz. ∑ A noise-voltage-density test is recommended when measuring noise on a large number of units. A 10 Hz noise-voltage- density measurement will correlate well with a 0.1 Hz to 10 Hz peak-to-peak noise reading, since both results are determined by the white noise and the location of the 1/f corner frequency. Instrumentation Amplifier Applications of the OP227 The excellent input characteristics of the OP227 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 CMR provide the characteristics needed for high performance instrumentation amplifiers. In addition, CMR versus frequency is very good due to the wide gain bandwidth of these op amps. The circuit of Figure 2 is recommended for applications where the common-mode input range is relatively low and differential gain will be in the range of 10 to 1000. This two op amp instrumentation amplifier features independent adjustment of common-mode rejection and differential gain. Input imped- ance is very high since both inputs are applied to non-inverting op amp inputs. R0 R2 R1 R4 R3 V1 A1 A2 VCM – 1/2Vd VCM + 1/2Vd VO VO = R4 R3 1+ 1 2 R2 R1 R3 R4 + R2 + R3 R0 Vd R4 R3 R3 R4 – R2 R1 VCM [ ( )+ ] + ( ) Figure 2. Two Op Amp Instrumentation Amplifier Configuration The output voltage VO, assuming ideal op amps, is given in Figure 2. 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/R1 to reject the common mode input VCM. The differential signal VO is then amplified according to: V R R R R RR R V where R R R R O O d =+ + + Ê ËÁ ˆ ¯˜ = 4 3 1 3 4 23 3 4 2 1 , 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 R1, R2, R3, and R4 approximately equal. Designing R1, R2, R3, and R4 as RN allows the output equation to be further simplified: V R R V where R R R R R O N O dN =+ Ê Ë Á ˆ ¯ ˜ = === 21 12 3 4 , |
Numéro de pièce similaire - OP227GY |
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Description similaire - OP227GY |
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