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AD745JR-16 Arkusz danych(PDF) 10 Page - Analog Devices |
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AD745JR-16 Arkusz danych(HTML) 10 Page - Analog Devices |
10 / 12 page REV. D AD745 –10– TWO HIGH PERFORMANCE ACCELEROMETER AMPLIFIERS Two of the most popular charge-out transducers are hydrophones and accelerometers. Precision accelerometers are typically cali- brated for a charge output (pC/g).* Figures 14 and 15 show two ways in which to configure the AD745 as a low noise charge amplifier for use with a wide variety of piezoelectric accelerom- eters. The input sensitivity of these circuits will be determined by the value of capacitor C1 and is equal to: ∆V OUT = ∆Q OUT C1 The ratio of capacitor C1 to the internal capacitance (CT) of the transducer determines the noise gain of this circuit (1 + CT/C1). The amplifiers voltage noise will appear at its output amplified by this amount. The low frequency bandwidth of these circuits will be dependent on the value of resistor R1. If a “T” network is used, the effective value is: R1 (1 + R2/R3). * pC = Picocoulombs g = Earth’s Gravitational Constant R3 1k R2 9k R1 110M (5 22M ) C1 1250pF B AND K 4370 OR EQUIVALENT OUTPUT 0.8mV/pC AD745 Figure 14. A Basic Accelerometer Circuit R3 1k R2 9k R1 110M (5 22M ) C1 1250pF AD745 B AND K 4370 OR EQUIVALENT OUTPUT 0.8mV/pC AD711 C2 2.2 F R4 18M R5 18M C3 2.2 F Figure 15. An Accelerometer Circuit Employing a DC Servo Amplifier A dc servo loop (Figure 15) can be used to assure a dc output <10 mV, without the need for a large compensating resistor when dealing with bias currents as large as 100 nA. For optimal low frequency performance, the time constant of the servo loop (R4C2 = R5C3) should be: Time Constant ≥10 R11+ R2 R3 C1 A LOW NOISE HYDROPHONE AMPLIFIER Hydrophones are usually calibrated in the voltage-out mode. The circuit of Figures 16 can be used to amplify the output of a typical hydrophone. If the optional ac coupling capacitor CC is used, the circuit will have a low frequency cutoff determined by an RC time constant equal to: Time Constant ≥ ×× 10 1 1 2 100 R CC πΩ where the dc gain is 1 and the gain above the low frequency cutoff (1/(2 π CC(100 Ω))) is equal to (1 + R2/R3). The circuit of Figure 17 uses a dc servo loop to keep the dc output at 0 V and to maintain full dynamic range for IB’s up to 100 nA. The time constant of R7 and C1 should be larger than that of R1 and CT for a smooth low frequency response. C1* CC R3 100 R2 1900 R4* CT R1 108 B AND K TYPE 8100 HYDROPHONE AD745 OUTPUT INPUT SENSITIVITY = –179dB RE. 1V/mPa** *OPTIONAL DC BLOCKING CAPACITOR **OPTIONAL, SEE TEXT Figure 16. A Low Noise Hydrophone Amplifier The transducer shown has a source capacitance of 7500 pF. For smaller transducer capacitances ( ≤300 pF), lowest noise can be achieved by adding a parallel RC network (R4 = R1, C1 = CT) in series with the inverting input of the AD745. C1* R3 100 R2 1900 CT R4* 108 AD745 OUTPUT AD711K R1 108 16M C2 0.27 F R5 100k R4 16M R6 1M DC OUTPUT 1mV FOR IB (AD745) 100nA *OPTIONAL, SEE TEXT Figure 17. A Hydrophone Amplifier Incorporating a DC Servo Loop |
Podobny numer części - AD745JR-16 |
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Podobny opis - AD745JR-16 |
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