EL2090 查看數據表（PDF） - Intersil
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EL2090 Datasheet PDF : 11 Pages
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EL2090
large a capacitor which slows the charge and discharge rate
of the stored voltage at Chold and too small a sampling
interval in which the entire feedback loop is closed.
The circuit shown above prevents the fault condition from
occurring by preventing the node from ever saturating. By
clamping the value of Chold to some value lower than the
supply voltage less a saturation voltage, we prevent this
node from approaching the positive rail. The maximum
voltage is set by the resistive voltage divider (between V+
and GND) R1 and R2 plus a diode. This value can be
adjusted if the maximum size of the input signal is known.
The diode used is an off-the-shelf 1N914 or 1N916.
As is true of all 100MHz amplifiers, good bypassing of the
supplies to ground is mandatory. 1µF tantalums are
sufficient, and 0.01µF leaded chip capacitors in parallel with
medium value electrolytics are also good. Pins longer than
1/2 can induce a characteristic 150MHz resonance and
ringing.
The VIN- of the video amplifier should have the absolute
minimum of parasitic capacitance. Stray capacitance of more
than 3pF will cause peaking and compromise the gain
flatness. The bandwidth of the amplifier is fundamentally set
by the value of Rf. As demonstrated by the frequency
response versus gain graph, the peaking and bandwidth is a
weak function of gain. The EL2090 was designed for
Rf = 300Ω giving optimum gain flatness at Av = +2. Unity-
gain response is flattest for Rf = 360Ω; gains of +5 can use
Rf = 270Ω. In situations where the peaking is accentuated by
load capacitance or -input capacitance the value of Rf will
have to be increased, and some bandwidth will be sacrificed.
The VIN+ of the video amplifier should not look into an
inductive source impedance. If the source is physically
remote and a terminated input line is not provided, it may be
necessary to connect an input “snubber” to ground. A
snubber is a resistor in series with a capacitor which de-Q's
the input resonance. Typical values are 100Ω and 30pF.
The output of the video amplifier is sensitive to capacitive
loads greater than 25pF, and a snubber to ground or a
resistor in series with the output is useful to isolate reactive
loads.
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