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AD8013ACHIPS 数据表(PDF) 9 Page - Analog Devices |
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AD8013ACHIPS 数据表(HTML) 9 Page - Analog Devices |
9 / 12 page –9– REV. A AD8013 FREQUENCY – Hz 1M 1G 10M 100M –6 +1 0 –1 –2 –3 –4 –5 180 90 0 –90 G = –10 RL = 150Ω VS = ±5V VS = +5V VS = +5V VS = ±5V GAIN PHASE Figure 27. Closed-Loop Gain and Phase vs. Frequency, G = –10, RL = 150 Ω To estimate the –3 dB bandwidth for closed-loop gains of 2 or greater, for feedback resistors not listed in the following table, the following single pole model for the AD8013 may be used: ACL G 1 + SC T ( RF + Gn rin ) where: CT = transcapacitance 1 pF RF = feedback resistor G = ideal closed loop gain Gn = 1 + R F R G = noise gain rin = inverting input resistance 150 Ω ACL = closed loop gain The –3 dB bandwidth is determined from this model as: f3 1 2 π C T ( RF + Gn rin ) This model will predict –3 dB bandwidth to within about 10% to 15% of the correct value when the load is 150 Ω and V S = ±5 V. For lower supply voltages there will be a slight decrease in bandwidth. The model is not accurate enough to predict either the phase behavior or the frequency response peaking of the AD8013. It should be noted that the bandwidth is affected by attenuation due to the finite input resistance. Also, the open-loop output resistance of about 12 Ω reduces the bandwidth somewhat when driving load resistors less than about 250 Ω. (Bandwidths will be about 10% greater for load resistances above a few hundred ohms.) Table I. –3 dB Bandwidth vs. Closed-Loop Gain and Feedback Resistor, RL = 150 Ω (SOIC) VS – Volts Gain RF – Ohms BW – MHz ±5 +1 2000 230 +2 845 (931) 150 (135) +10 301 80 –1 698 (825) 140 (130) –10 499 85 +5 +1 2000 180 +2 887 (931) 120 (130) +10 301 75 –1 698 (825) 130 (120) –10 499 80 Driving Capacitive Loads When used in combination with the appropriate feedback resistor, the AD8013 will drive any load capacitance without oscillation. The general rule for current feedback amplifiers is that the higher the load capacitance, the higher the feedback resistor required for stable operation. Due to the high open-loop transresistance and low inverting input current of the AD8013, the use of a large feedback resistor does not result in large closed- loop gain errors. Additionally, its high output short circuit current makes possible rapid voltage slewing on large load capacitors. For the best combination of wide bandwidth and clean pulse response, a small output series resistor is also recommended. Table II contains values of feedback and series resistors which result in the best pulse responses. Figure 29 shows the AD8013 driving a 300 pF capacitor through a large voltage step with virtually no overshoot. (In this case, the large and small signal pulse responses are quite similar in appearance.) General The AD8013 is a wide bandwidth, triple video amplifier that offers a high level of performance on less than 4.0 mA per amplifier of quiescent supply current. The AD8013 uses a proprietary enhancement of a conventional current feedback architecture, and achieves bandwidth in excess of 200 MHz with low differential gain and phase errors, making it an extremely efficient video amplifier. The AD8013’s wide phase margin coupled with a high output short circuit current make it an excellent choice when driving any capacitive load. High open-loop gain and low inverting input bias current enable it to be used with large values of feedback resistor with very low closed-loop gain errors. It is designed to offer outstanding functionality and performance at closed-loop inverting or noninverting gains of one or greater. Choice of Feedback & Gain Resistors Because it is a current feedback amplifier, the closed-loop band- width of the AD8013 may be customized using different values of the feedback resistor. Table I shows typical bandwidths at different supply voltages for some useful closed-loop gains when driving a load of 150 Ω. The choice of feedback resistor is not critical unless it is important to maintain the widest, flattest frequency response. The resistors recommended in the table are those (chip resistors) that will result in the widest 0.1 dB bandwidth without peaking. In applications requiring the best control of bandwidth, 1% resistors are adequate. Package parasitics vary between the 14-pin plastic DIP and the 14-pin plastic SOIC, and may result in a slight difference in the value of the feedback resistor used to achieve the optimum dynamic performance. Resistor values and widest bandwidth figures are shown in parenthesis for the SOIC where they differ from those of the DIP. Wider bandwidths than those in the table can be attained by reducing the magnitude of the feedback resistor (at the expense of increased peaking), while peaking can be reduced by increasing the magnitude of the feedback resistor. Increasing the feedback resistor is especially useful when driving large capacitive loads as it will increase the phase margin of the closed-loop circuit. (Refer to the section on driving capacitive loads for more information.) |
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类似说明 - AD8013ACHIPS |
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