Published:2009/6/24 3:18:00 Author:May
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Published:2009/6/24 3:14:00 Author:May
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Published:2009/6/24 3:13:00 Author:May
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Published:2009/6/24 3:13:00 Author:May
This circuit offers the best of both worlds, It can be combined with a low input offset voltage and drift without degrading the overall system's dynamic performance. Compared to a standalone FETinput operational amplifier, the composite amplifier circuit exhibits a 20-fold improvement in voltage offset and drift.
In this circuit arrangement, A1 is a highspeed FET input op amp with a closed-loop gain of 100 (the source impedance was arbitrarily chosen to be 100 kΩ). A2 is a SuperBeta bipolar input op amp. It has good dc characteristics, biFET-level input bias current, and low noise. A2 monitdrs the voltage at the input of Al and injects current to Al's null pins. This forces A1 to have the input properties of a bipolar amplifier while maintaining its bandwidth and low-inputbias-current noise. (View)
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Published:2009/6/24 3:12:00 Author:May
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Published:2009/6/24 3:10:00 Author:May
This circuit has less than 2% distortion and is flat within 3 dB from 15 Hz to 130 kHz. (View)
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Published:2009/6/24 3:18:00 Author:Jessie
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Published:2009/6/24 3:17:00 Author:Jessie
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Published:2009/6/24 3:15:00 Author:Jessie
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Published:2009/6/24 3:15:00 Author:Jessie
You can build a composite amplifier featuring high gain, wide bandwidth, and good dc accuracy by cascading the sections of a dual video amplifier and adding two appropriate phase-compensation components. The op amp drives a 150-Ω load and provides a closed-loop gain of 40 dB. (View)
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Published:2009/6/24 3:08:00 Author:May
This switch is in series with feedback resistor to compensate gain. (View)
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Published:2009/6/24 3:04:00 Author:May
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Published:2009/6/24 3:10:00 Author:Jessie
A JFET acts as a variable attenuator for this op amp. Maximum gain is: (View)
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Published:2009/6/24 3:04:00 Author:May
Using resistor and transistor feedback elements, this operational amplifier circuit can be used as a nonlinear amplifier. R4 and R6 can be varied to change breakpoints, as required. (View)
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Published:2009/6/24 3:03:00 Author:May
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Published:2009/6/24 3:02:00 Author:May
A clamp-on current probe, such as the Tektronix P6021, is a useful means of displaying current waveforms on an oscilloscope. A less-expensive and simple alternative is shown in the figure.The more sensitive range on the P6021 is 2 mA/mV, but it has a roll-off of 6-dB per octave below 450 Hz. The purpose of the compensator is to counteract the low-frequency attenuation, which is achieved by means of C3 and R4 + P1 in the feedback around op amp N1. It's important that the latter is a low-noise type, such as the LM725 shown in the figure. On top of that, it's necessary at some point to limit the increasing gain with decreasing frequency; otherwise, amplifier noise and drive will overcome the signal. The values shown for C3 and R3 give a lower limit of less than 1 Hz.A test square wave of ±1 mA is fed to the current probe so that P1 can be adjusted for minimum droop or overshoot in the output waveform. It's vital that the sliding core on the probe is fully closed. At high frequencies, the response begins to fall off at 100 kHz. Therefore, for most waveforms, switch S1 is moved to direct, above a fundamental frequency of, for example, 10 kHz.This circuit's current consumption is quite low, and it can be battery powered. If a mains power supply is built-in, it must be well screened to prevent hum problems. (View)
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Published:2009/6/24 3:08:00 Author:Jessie
This circuit from Apex Microtechnology can deliver 180 V p-p@90 kHz into a 4-Ωload.The PA04 can deliver 400-W RMS into an 8-Ω load with low THD at frequencies beyond 20 kHz. (View)
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Published:2009/6/24 3:08:00 Author:Jessie
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Published:2009/6/24 3:08:00 Author:Jessie
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Published:2009/6/24 3:07:00 Author:Jessie
The low-noise precision FET op-amp AD795 has around 1014-Ω common-mode impedance, lowoffset voltage (250 μVmax) and L13 μVC drift make this device ideal for low-voltage measurements from high-impedance sources. (View)
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