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CLC451 Operation
The CLC451 is a current feedback buffer built in an
advanced complementary bipolar process. The CLC451
operates from a single 5V supply or dual ±5V supplies.
Operating from a single 5V supply, the CLC451 has the
following features:
I
Gains of +1, -1, and 2V/V are achievable without
external resistors
I
Provides 100mA of output current while
consuming only 7.5mW of power
I
Offers low -66/-75dBc 2nd and 3rd harmonic
distortion
I
Provides BW > 60MHz and 1MHz distortion
< -55dBc at V
o
= 2V
pp
The CLC451 performance is further enhanced in ±5V
supply applications as indicated in the
±5V Electrical
Characteristics
table and
±5V Typical Performance
plots.
If gains other than +1, -1, or +2V/V are required, then the
CLC450 can be used. The CLC450 is a current feedback
amplifier with near identical performance and allows for
external feedback and gain setting resistors.
Current Feedback Amplifiers
Some of the key features of current feedback technology are:
I
Independence of AC bandwidth and voltage gain
I
Inherently stable at unity gain
I
Adjustable frequency response with feedback resistor
I
High slew rate
I
Fast settling
Current feedback operation can be described using a simple
equation. The voltage gain for a non-inverting or inverting
current feedback amplifier is approximated by Equation 1.
Equation 1
where:
I
A
v
is the closed loop DC voltage gain
I
R
f
is the feedback resistor
I
Z(j
ω
) is the CLC451’s open loop transimpedance
gain
Z j
R
f
I
is the loop gain
The denominator of Equation 1 is approximately equal to
1 at low frequencies. Near the -3dB corner frequency, the
interaction between R
f
and Z(j
ω
) dominates the circuit
performance. The value of the feedback resistor has a
large affect on the circuits performance. Increasing R
f
has the following affects:
I
Decreases loop gain
I
Decreases bandwidth
I
Reduces gain peaking
I
Lowers pulse response overshoot
I
Affects frequency response phase linearity
V
V
A
1
R
Z(j )
o
in
v
f
=
+
ω
( )
CLC451 Design Information
Closed Loop Gain Selection
The CLC451 is a current feedback op amp with
R
f
= R
g
= 1k
on chip (in the package). Select from
three closed loop gains without using any external gain or
feedback resistors. Implement gains of +2, +1, and
-1V/V by connecting pins 2 and 3 as described in the
chart below.
The gain accuracy of the CLC451 is excellent and
stable over temperature change.
setting resistors, R
f
and R
g
are diffused silicon resistors
with a process variation of ± 20% and a temperature
coefficient of 2000ppm/°C.
values change with processing and temperature, their
ratio (R
f
/R
g
) remains constant. If an external resistor is
used in series with R
g
, gain accuracy over temperature
will suffer.
The internal gain
Although their absolute
Single Supply Operation (V
CC
= +5V,V
EE
= GND)
The specifications given in the
+5V Electrical Character-
istics
table for single supply operation are measured with
a common mode voltage (V
cm
) of 2.5V. V
cm
is the volt-
age around which the inputs are applied and the
output voltages are specified.
Operating from a single +5V supply, the Common Mode
Input Range (CMIR) of the CLC451 is typically +0.8V to
+4.2V. The typical output range with R
L
=100
is +1.0V
to +4.0V.
For single supply DC coupled operation, keep input
signal levels above 0.8V DC. For input signals that drop
below 0.8V DC, AC coupling and level shifting the signal
are recommended. The non-inverting and inverting
configurations for both input conditions are illustrated in
the following 2 sections.
DC Coupled Single Supply Operation
Figures 1, 2, and 3 on the following page, show the
recommended configurations for input signals that
remain above 0.8V DC.
Gain
A
v
-1V/V
+1V/V
+2V/V
Input Connections
Non-Inverting (pin3)
Inverting (pin2)
ground
input signal
input signal
input signal
NC (open)
ground