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AD8001 Scheda tecnica(PDF) 11 Page - Analog Devices |
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AD8001 Scheda tecnica(HTML) 11 Page - Analog Devices |
11 / 16 page REV. D AD8001 –11– Printed Circuit Board Layout Considerations As to be expected for a wideband amplifier, PC board parasitics can affect the overall closed-loop performance. Of concern are stray capacitances at the output and the inverting input nodes. If a ground plane is to be used on the same side of the board as the signal traces, a space (5 mm min) should be left around the signal lines to minimize coupling. Additionally, signal lines connecting the feedback and gain resistors should be short enough so that their associated inductance does not cause high frequency gain errors. Line lengths on the order of less than 5 mm are recommended. If long runs of coaxial cable are being driven, dispersion and loss must be considered. Power Supply Bypassing Adequate power supply bypassing can be critical when optimiz- ing the performance of a high frequency circuit. Inductance in the power supply leads can form resonant circuits that produce peaking in the amplifier’s response. In addition, if large current transients must be delivered to the load, then bypass capacitors (typically greater than 1 µF) will be required to provide the best settling time and lowest distortion. A parallel combination of 4.7 µF and 0.1 µF is recommended. Some brands of electrolytic capacitors will require a small series damping resistor ≈4.7 Ω for optimum results. DC Errors and Noise There are three major noise and offset terms to consider in a current feedback amplifier. For offset errors, refer to the equation below. For noise error the terms are root-sum-squared to give a net output error. In the circuit in Figure 7 they are input offset (VIO), which appears at the output multiplied by the noise gain of the circuit (1 + RF/RI), noninverting input current (IBN × R N) also multiplied by the noise gain, and the inverting input current, which when divided between RF and RI and subsequently multiplied by the noise gain always appears at the output as IBN ×RF. The input voltage noise of the AD8001 is a low 2 nV/ √Hz. At low gains though the inverting input current noise times RF is the dominant noise source. Careful layout and device matching contribute to better offset and drift specifications for the AD8001 compared to many other current feedback ampli- fiers. The typical performance curves in conjunction with the following equations can be used to predict the performance of the AD8001 in any application. VV R R IR R R IR OUT IO F I BN N F I BI F =× + ±× × + ±× 11 RF RI RN IBN VOUT IBI Figure 7. Output Offset Voltage Driving Capacitive Loads The AD8001 was designed primarily to drive nonreactive loads. If driving loads with a capacitive component is desired, best frequency response is obtained by the addition of a small series resistance, as shown in Figure 8. The accompanying graph shows the optimum value for RSERIES versus capacitive load. It is worth noting that the frequency response of the circuit when driving large capacitive loads will be dominated by the passive roll-off of RSERIES and CL. 909 RSERIES RL 500 IN CL Figure 8. Driving Capacitive Loads 40 0 0 25 30 10 5 20 15 20 10 CL – pF G = +1 Figure 9. Recommended RSERIES vs. Capacitive Load |
Codice articolo simile - AD8001_03 |
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Descrizione simile - AD8001_03 |
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