el2160 Intersil Corporation, el2160 Datasheet - Page 11

• Manufacturer Part Number: el2160
• Description: 180mhz Current Feedback Amplifier
• Manufacturer: Intersil Corporation

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, below ¼”. The power supply pins must
be well bypassed to reduce the risk of oscillation. A 1.0µF
tantalum capacitor in parallel with a 0.01µF ceramic
capacitor is adequate for each supply pin.
For good AC performance, parasitic capacitances should be
kept to a minimum, especially at the inverting input (see
Capacitance at the Inverting Input section). This implies
keeping the ground plane away from this pin. Carbon
resistors are acceptable, while use of wire-wound resistors
should not be used because of their parasitic inductance.
Similarly, capacitors should be low inductance for best
performance. Use of sockets, particularly for the SO
package, should be avoided. Sockets add parasitic
inductance and capacitance which will result in peaking and
overshoot.
Capacitance at the Inverting Input
Due to the topology of the current feedback amplifier, stray
capacitance at the inverting input will affect the AC and
transient performance of the EL2160 when operating in the
non-inverting configuration. The characteristic curve of gain
vs. frequency with variations of C
The curve illustrates how the bandwidth can be extended to
beyond 200MHz with some additional peaking with an
additional 2pF of capacitance at the V
A
obtain similar effects at higher gains.
In the inverting gain mode, added capacitance at the
inverting input has little effect since this point is at a virtual
ground and stray capacitance is therefore not “seen” by the
amplifier.
Feedback Resistor Values
The EL2160 has been designed and specified with
R
extremely flat frequency response with little to no peaking
out to 130MHz. As is the case with all current feedback
amplifiers, wider bandwidth, at the expense of slight peaking,
can be obtained by reducing the value of the feedback
resistor. Inversely, larger values of feedback resistor will
cause rolloff to occur at a lower frequency. By reducing R
430:, bandwidth can be extended to 170MHz with under
1dB of peaking. Further reduction of R
the bandwidth to 195MHz with about 2.5dB of peaking. See
the curves in the Typical Performance Curves section which
show 3dB bandwidth and peaking vs. frequency for various
feedback resistors and various supply voltages.
V
F
= +2. Higher values of capacitance will be required to
= 560: for A
V
= +2. This value of feedback resistor yields
11
IN
- emphasizes this effect.
IN
F
- pin for the case of
to 360: increases
F
to
EL2160
Bandwidth vs Temperature
Whereas many amplifier's supply current and consequently
3dB bandwidth drop off at high temperature, the EL2160 was
designed to have little supply current variations with
temperature. An immediate benefit from this is that the 3dB
bandwidth does not drop off drastically with temperature.
With V
150MHz to 110MHz over the entire die junction temperature
range of 0°C < T < 15 0°C .
Supply Voltage Range
The EL2160 has been designed to operate with supply
voltages from ±2V to ±15V. Optimum bandwidth, slew rate,
and video characteristics are obtained at higher supply
voltages. However, at ±2V supplies, the 3dB bandwidth at
A
oscilloscope plot of the EL2160 at ±2V supplies, A
R
±600mV signal at the output.
If a single supply is desired, values from +4V to +30V can be
used as long as the input common mode range is not
exceeded. When using a single supply, be sure to either 1)
DC bias the inputs at an appropriate common mode voltage
and AC couple the signal, or 2) ensure the driving signal is
within the common mode range of the EL2160.
Settling Characteristics
The EL2160 offers superb settling characteristics to 0.1%,
typically in the 35ns to 40ns range. There are no aberrations
created from the input stage which often cause longer
settling times in other current feedback amplifiers. The
EL2160 is not slew rate limited, therefore any size step up to
±10V gives approximately the same settling time.
As can be seen from the Long Term Settling Error curve, for
A
tails away to 0.01% in about 40µs. This is a thermal settling
error caused by a power dissipation differential (before and
after the voltage step). For A
mode configuration, this tail does not appear since the input
stage does not experience the large voltage change as in the
non-inverting mode. With A
slightly greater than 100ns.
V
V
F
= +2 is a respectable 70MHz. The following figure is an
= +1, there is approximately a 0.035% residual which
= R
S
G
= ±15V and A
= 560:, driving a load of 150:, showing a clean
V
= +2, the bandwidth only varies from
V
V
= -1, 0.01% settling time is
= -1, due to the inverting
V
= +2,