EL5191CS-T13 ELANTEC [Elantec Semiconductor], EL5191CS-T13 Datasheet - Page 12
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EL5191CS-T13
Manufacturer Part Number
EL5191CS-T13
Description
1GHz Current Feedback Amplifier
Manufacturer
ELANTEC [Elantec Semiconductor]
Datasheet
1.EL5191CS-T13.pdf
(17 pages)
EL5191C
1GHz Current Feedback Amplifier
Applications Information
Product Description
The EL5191C is a current-feedback operational ampli-
fier that offers a wide -3dB bandwidth of 1GHz and a
low supply current of 9mA per amplifier. The EL5191C
works with supply voltages ranging from a single 5V to
10V and they are also capable of swinging to within 1V
of either supply on the output. Because of their current-
feedback topology, the EL5191C does not have the nor-
mal gain-bandwidth product associated with voltage-
feedback operational amplifiers. Instead, its -3dB band-
width to remain relatively constant as closed-loop gain is
increased. This combination of high bandwidth and low
power, together with aggressive pricing make the
EL5191C the ideal choice for many low-power/high-
bandwidth applications such as portable, handheld, or
battery-powered equipment.
For varying bandwidth needs, consider the EL5192C
with 600MHz on a 6mA supply current or the EL5193C
with 300MHz on a 4mA supply current. Versions
include single, dual, and triple amp packages with 5-pin
SOT23, 16-pin QSOP, and 8-pin or 16-pin SO outlines.
Power Supply Bypassing and Printed Circuit
Board Layout
As with any high frequency device, good printed circuit
board layout is necessary for optimum performance.
Low impedance ground plane construction is essential.
Surface mount components are recommended, but if
leaded components are used, lead lengths should be as
short as possible. The power supply pins must be well
bypassed to reduce the risk of oscillation. The combina-
tion of a 4.7µF tantalum capacitor in parallel with a
0.01µF capacitor has been shown to work well when
placed at each supply pin.
For good AC performance, parasitic capacitance should
be kept to a minimum, especially at the inverting input.
(See the Capacitance at the Inverting Input section) Even
when ground plane construction is used, it should be
removed from the area near the inverting input to mini-
mize any stray capacitance at that node. Carbon or
Metal-Film resistors are acceptable with the Metal-Film
resistors giving slightly less peaking and bandwidth
because of additional series inductance. Use of sockets,
12
particularly for the SO package, should be avoided if
possible. Sockets add parasitic inductance and capaci-
tance which will result in additional peaking and
overshoot.
Capacitance at the Inverting Input
Any manufacturer’s high-speed voltage- or current-
feedback amplifier can be affected by stray capacitance
at the inverting input. For inverting gains, this parasitic
capacitance has little effect because the inverting input is
a virtual ground. But for non-inverting gains, this capac-
itance (in conjunction with the feedback and gain
resistors) creates a pole in the feedback path of the
amplifier. This pole, if low enough in frequency, has the
same destabilizing effect as a zero in the forward open-
loop response. The use of large value feedback and gain
resistors exacerbates the problem by further lowering
the pole frequency (increasing the possibility of
oscillation.)
The EL5191C has been optimized with a 250 feedback
resistor. With the high bandwidth of these amplifiers,
these resistor values might cause stability problems
when combined with parasitic capacitance, thus ground
plane is not recommended around the inverting input pin
of the amplifier.
Feedback Resistor Values
The EL5191C has been designed and specified at a gain
of +2 with R
back resistor gives 600MHz of -3dB bandwidth at A
with about 2dB of peaking. With A
gives 450MHz of bandwidth with 0.6dB of peaking.
Since the EL5191C is a current-feedback amplifier, it is
also possible to change the value of R
width. As seen in the curve of Frequency Response for
Various R
ily modified by varying the value of the feedback
resistor.
Because the EL5191C is a current-feedback amplifier,
its gain-bandwidth product is not a constant for different
closed-loop gains. This feature actually allows the
EL5191C to maintain about the same -3dB bandwidth.
As gain is increased, bandwidth decreases slightly while
F
and R
F
approximately 250 . This value of feed-
G
, bandwidth and peaking can be eas-
V
F
=-2, that same R
to get more band-
V
=2
F