el2360 Intersil Corporation, el2360 Datasheet - Page 10

• Manufacturer Part Number: el2360
• Description: Triple 130mhz Current Feedback Amplifier
• Manufacturer: Intersil Corporation

Simplified Schematic (One Amplifier)
Applications Information
Product Description
The EL2360 is a triple current feedback amplifier that offers
wide bandwidth and good video specifications at moderately
low supply currents. It is built using Elantec’s proprietary
complimentary bipolar process and is offered in both a 16-
pin PDIP and SOIC packages. Due to the current feedback
architecture, the EL2360 closed-loop -3dB bandwidth is
dependent on the value of the feedback resistor. First the
desired bandwidth is selected by choosing the feedback
resistor, R
resistor, R
Performance Curves section show the effect of varying both
R
the power supply voltage. As the supply voltage is
decreased, internal junction capacitances increase, causing
a reduction in the closed loop bandwidth. To compensate for
this, smaller values of feedback resistor can be used at lower
supply voltages.
Power Supply Bypassing and Printed Circuit
Board Layout
As with any high-frequency device, good printed circuit
board layout is necessary for optimum performance. Ground
plane construction is highly recommended. Lead lengths
should be as short as possible, preferably below 1/4”. The
power supply pins must be well bypassed to reduce the risk
of oscillation. The combination of a 1.0µF tantalum capacitor
in parallel with a 0.01µF ceramic 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). This implies
F
and R
G.
F
G
, and then the gain is set by picking a gain
. The curves at the beginning of the Typical
The -3dB bandwidth is somewhat dependent on
10
EL2360
keeping the ground plane away from this pin. Carbon or
Metal-Film resistors are acceptable with the Metal-Film
resistors giving slightly less peaking and bandwidth because
of their additional series inductance. Use of sockets,
particularly for the SO package should be avoided if
possible. Sockets add parasitic inductance and capacitance
which will result in some 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. The characteristic curve of gain vs. frequency
with variations in C
illustrates how the bandwidth can be extended to beyond
200MHz with some additional peaking with an additional 2pF
of capacitance at the V
parasitic capacitance has little effect because the inverting
input is a virtual ground, but for non-inverting gains, this
capacitance (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 further exacerbates the problem by further lowering
the pole frequency.
Feedback Resistor Values
The EL2360 has been designed and specified at a gain of +2
with R
relatively flat frequency response with little to no peaking out
to 130MHz. Since the EL2360 is a current-feedback
amplifier, it is also possible to change the value of R
more bandwidth. As seen in the curve of Frequency
Response For Various R
F
= 560:. This value of feedback resistor yields
IN
- emphasizes this effect. The curve
IN
F
- pin. For inverting gains, this
and R
G
, bandwidth and peaking
F
to get