LMH6628EP Datasheet, PDF (12/16 Pages) National Semiconductor (TI) – Enhanced Plastic Dual Wideband, Low Noise, Voltage Feedback Op Amp

FIGURE 4.
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POSITIVE PEAK DETECTOR
The LMH6628EP's dual amplifiers can be used to implement
a unity-gain peak detector circuit as shown in Figure 5.
FIGURE 6.
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A current source, built around Q1, provides the necessary
bias current for the second amplifier and prevents saturation
when power is applied. The resistor, R, closes the loop while
diode D2 prevents negative saturation when V_IN is less than
V_C. A MOS-type switch (not shown) can be used to reset the
capacitor's voltage.
The maximum speed of detection is limited by the delay of the
op amps and the diodes. The use of Schottky diodes will pro-
vide faster response.
ADJUSTABLE OR BANDPASS EQUALIZER
A "boost" equalizer can be made with the LMH6628EP by
summing a bandpass response with the input signal, as
shown in Figure 7.
FIGURE 5.
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The acquisition speed of this circuit is limited by the dynamic
resistance of the diode when charging C_hold. A plot of the
circuit's performance is shown in Figure 6 with a 1MHz sinu-
soidal input.
FIGURE 7.
The overall transfer function is shown in Eq. 5.
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(4)
To build a boost circuit, use the design equations Eq. 6 and
Eq. 7.
(5)
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200886 Version 4 Revision 2 Print Date/Time: 2010/10/15 15:22:20