el8302 Intersil Corporation, el8302 Datasheet - Page 9

• Manufacturer Part Number: el8302
• Description: 500mhz Rail-to-rail Amplifier
• Manufacturer: Intersil Corporation

Simplified Schematic Diagram
Description of Operation and Application
Information
Product Description
The EL8302 is wide bandwidth, single supply, low power and
rail-to-rail output voltage feedback operational amplifiers.
The amplifiers are internally compensated for closed loop
gain of +1 of greater. Connected in voltage follower mode
and driving a 1kΩ load, the EL8302 has a -3dB bandwidth of
500MHz. Driving a 150Ω load, the bandwidth is about
350MHz while maintaining a 600V/us slew rate. The EL8302
is available with a power down pin for each channel to
reduce power to 30µA typically while the amplifier is
disabled.
Input, Output and Supply Voltage Range
The EL8302 has been designed to operate with a single
supply voltage from 3V to 5.0V. Split supplies can also be
used as long as their total voltage is within 3V to 5.0V. The
amplifiers have an input common mode voltage range from
0.15V below the negative supply (V
the positive supply (V
above specified range, it will cause the output signal to be
distorted.
The output of the EL8302 can swing rail to rail. As the load
resistance becomes lower, the ability to drive close to each
rail is reduced. For the load resistor 1kΩ, the output swing is
about 4.9V at a 5V supply. For the load resistor 150Ω, the
output swing is about 4.6V.
Choice of Feedback Resistor and Gain Bandwidth
Product
For applications that require a gain of +1, no feedback
resistor is required. Just short the output pin to the inverting
input pin. For gains greater than +1, the feedback resistor
forms a pole with the parasitic capacitance at the inverting
S
+ pin). If the input signal is outside the
IN+
I
1
9
Q
1
R
1
S
R
- pin) to within 1.5V of
3
Q
2
R
I
V
2
2
BIAS2
IN-
Q
5
Q
R
R
3
6
4
EL8302
Q
6
Q
V
V
R
R
4
S+
input. As this pole becomes smaller, the amplifier’s phase
margin is reduced. This causes ringing in the time domain
and peaking in the frequency domain. Therefore, R
some maximum value that should not be exceeded for
optimum performance. If a large value of R
small capacitor in the few pF range in parallel with R
help to reduce the ringing and peaking at the expense of
reducing the bandwidth.
As far as the output stage of the amplifier is concerned, the
output stage is also a gain stage with the load. R
appear in parallel with R
combination gets smaller, the bandwidth falls off.
Consequently, R
be exceeded for optimum performance. For gain of +1, R
is optimum. For the gains other than +1, optimum response
is obtained with R
The EL8302 has a gain bandwidth product of 200MHz. For
gains ≥5, its bandwidth can be predicted by the following
equation:
Video Performance
For good video performance, an amplifier is required to
maintain the same output impedance and the same
frequency response as DC levels are changed at the output.
This is especially difficult when driving a standard video load
of 150Ω, because the change in output current with DC level.
Special circuitry has been incorporated in the EL8302 to
reduce the variation of the output impedance with the current
output. This results in dG and dP specifications of 0.01%
and 0.01°, while driving 150Ω at a gain of 2. Driving high
impedance loads would give a similar or better dG and dP
performance.
Gain
S-
7
5
V
BIAS1
×
BW
DIFFERENTIAL TO
SINGLE ENDED
GENERATOR
=
DRIVE
200MHz
F
F
also has a minimum value that should not
between 300Ω to 1kΩ.
L
for gains other than +1. As this
Q
Q
7
8
R
R
8
9
OUT
F
must be used, a
F
and R
F
F
has
can
F
G
=0