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AD8044ARZ-14-REEL датащи(PDF) 11 Page - Analog Devices |
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AD8044ARZ-14-REEL датащи(HTML) 11 Page - Analog Devices |
11 / 16 page AD8044 REV. B –11– Overdrive Recovery Overdrive of an amplifier occurs when the output and/or input range are exceeded. The amplifier must recover from this over- drive condition. As shown in Figure 33, the AD8044 recovers within 50 ns from negative overdrive and within 25 ns from positive overdrive. 50ns 1V VS = +5V AV = +2 RF = 2k RL = 2k VIN 2V/DIV VOUT 1V/DIV 2V Figure 33. Overdrive Recovery, VS + 5 V, VIN = 4 V Step Circuit Description The AD8044 is fabricated on Analog Devices’ proprietary eXtra-Fast Complementary Bipolar (XFCB) process which enables the construction of PNP and NPN transistors with similar fTs in the 2 GHz–4 GHz region. The process is dielectri- cally isolated to eliminate the parasitic and latch-up problems caused by junction isolation. These features allow the construc- tion of high frequency, low distortion amplifiers with low supply currents. This design uses a differential output input stage to maximize bandwidth and headroom (see Figure 34). The smaller signal swings required on the first stage outputs (nodes S1P, S1N) reduce the effect of nonlinear currents due to junction capacitances and improve the distortion performance. With this design harmonic distortion of better than –85 dB @ 1 MHz into 100 W with VOUT = 2 V p-p (Gain = +2) on a single 5 volt supply is achieved. The AD8044’s rail-to-rail output range is provided by a comple- mentary common-emitter output stage. High output drive capa- bility is provided by injecting all output stage predriver currents directly into the bases of the output devices Q8 and Q36. Bias- ing of Q8 and Q36 is accomplished by I8 and I5, along with a common-mode feedback loop (not shown). This circuit topol- ogy allows the AD8044 to drive 50 mA of output current with the outputs within 0.5 V of the supply rails. On the input side, the device can handle voltages from –0.2 V below the negative rail to within 1.2 V of the positive rail. Ex- ceeding these values will not cause phase reversal; however, the input ESD devices will begin to conduct if the input voltages exceed the rails by greater than 0.5 V. Driving Capacitance Loads The capacitive load drive of the AD8044 can be increased by adding a low valued resistor in series with the load. Figure 35 shows the effects of a series resistor on capacitive drive for vary- ing voltage gains. As the closed-loop gain is increased, the larger phase margin allows for larger capacitive loads with less over- shoot. Adding a series resistor with lower closed-loop gains accomplishes this same effect. For large capacitive loads, the frequency response of the amplifier will be dominated by the roll-off of the series resistor and capacitive load. SIN R21 R3 VEE Q11 Q3 I10 R26 R39 Q5 Q4 Q40 I7 R2 R15 Q13 Q17 R5 C7 Q2 SIP Q22 Q7 Q21 Q24 R23 R27 I2 I3 I1 Q51 Q25 Q50 Q39 Q47 Q27 Q31 Q23 I9 I5 VEE VCC I8 Q36 Q8 VOUT C3 C9 VCC VINP VINN VEE I11 Figure 34. AD8044 Simplified Schematic |
Аналогичный номер детали - AD8044ARZ-14-REEL |
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Аналогичное описание - AD8044ARZ-14-REEL |
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