Datasheet

LMH6628
www.ti.com SNOSA02D –MAY 2002–REVISED MARCH 2013
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 provide faster response.
ADJUSTABLE OR BANDPASS EQUALIZER
A "boost" equalizer can be made with the LMH6628 by summing a bandpass response with the input signal, as
shown in Figure 34.
Figure 34. "Boost" Equalizer Made With the LMH6628 by Summing a Bandpass Response With the Input
Signal
The overall transfer function is shown in Equation 4.
(4)
To build a boost circuit, use the design equations Equation 5 and Equation 6.
(5)
(6)
Select R
2
and C using Equation 5. Use reasonable values for high frequency circuits - R
2
between 10Ω and 5kΩ,
C between 10pF and 2000pF. Use Equation 6 to determine the parallel combination of R
a
and R
b
. Select R
a
and
R
b
by either the 10Ω to 5kΩ criteria or by other requirements based on the impedance V
in
is capable of driving.
Finish the design by determining the value of K from Equation 7.
(7)
Figure 35 shows an example of the response of the circuit of Figure 34, where f
o
is 2.3MHz. The component
values are as follows: R
a
=2.1kΩ, R
b
= 68.5Ω, R
2
= 4.22kΩ, R = 500Ω, KR = 50Ω, C = 120pF.
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