el2166 Intersil Corporation, el2166 Datasheet - Page 11

• Manufacturer Part Number: el2166
• Description: 110mhz Current Feedback Amplifier With Disable
• Manufacturer: Intersil Corporation

Applications Information
Product Description
The EL2166 is a current mode feedback amplifier that offers
wide bandwidth and good video specifications at a
moderately low supply current. It is built using Elantec's
proprietary complimentary bipolar process and is offered in
industry standard pin-outs. Due to the current feedback
architecture, the EL2166 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. The bandwidth reduces from
110MHz to 95MHz as supplies are varied from ±15V to ±5V.
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, below 1/4”. 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 EL2166 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
over 30MHz with some additional peaking with an additional
5pF of capacitance at the V
Higher values of capacitance will be required to 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
F
and R
G
F
G
. The 3dB bandwidth is only slightly dependent on
, and then the gain is set by picking the gain
. The curves at the beginning of the Typical
IN
11
- pin for the case of A
IN
- emphasizes this effect.
V
= +2.
EL2166
ground and stray capacitance is therefore not “seen” by the
amplifier.
Feedback Resistor Values
The EL2166 has been designed and specified with
R
relatively flat frequency response with < 1.5dB peaking out
to 110MHz. 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 120MHz with 4.5dB 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.
Bandwidth vs Temperature
Whereas many amplifier's supply current and consequently
3dB bandwidth drop off at high temperature, the EL2166 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
115MHz to 95MHz over the entire die junction temperature
range of 0°C < T < 15 0°C .
Supply Voltage Range
The EL2166 has been designed to operate with supply
voltages from ±5V to ±15V. AC performance, including -3dB
bandwidth and differential gain and phase, shows little
degradation as the supplies are lowered to ±5V. For
example, as supplies are lowered from ±15V to ±5V, -3dB
bandwidth reduces only 15MHz, and differential gain and
phase remain less than 0.05%/0.02° re spectively.
If a single supply is desired, values from +10V 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 EL2166.
Disable Function
The EL2166 has a superior disable function that has been
optimized for video performance. Time to disable/enable is
around 75ns.
During disable, the output of the EL2166 can withstand over
1500V/µs slew rate signals at its output and the output does
not draw excessive currents. The feed-through can be
modeled as a 1.5pF capacitor from V
the output impedance can be modeled as 4.4pF in parallel
with 180k: to ground when disabled. Consequently,
multiplexing with the EL2166 is very easy. Simply tie the
outputs of multiple EL2166s together and drive the
/DISABLE pins with standard TTL or CMOS signals. The
F
= 560: for A
S
= ±15V and A
V
= +2. This value of feedback resistor yields
V
= +2, the bandwidth only varies from
IN
+ to the output, and
F
to