CLC1603IST6X CADEKA [Cadeka Microcircuits LLC.], CLC1603IST6X Datasheet - Page 14

• Manufacturer Part Number: CLC1603IST6X
• Description: Single and Triple, 1.1mA, 200MHz Amplifiers
• Manufacturer: CADEKA [Cadeka Microcircuits LLC.]

Data Sheet
General Information - Current Feedback
Technology
Advantages of CFB Technology
The CLCx603 Family of amplifiers utilize current feedback
(CFB) technology to achieve superior performance. The
primary advantage of CFB technology is higher slew rate
performance when compared to voltage feedback (VFB)
architecture. High slew rate contributes directly to better
large signal pulse response, full power bandwidth, and
distortion.
CFB also alleviates the traditional trade-off between
closed loop gain and usable bandwidth that is seen with
a VFB amplifier. With CFB, the bandwidth is primarily de-
termined by the value of the feedback resistor, R
ing optimum feedback resistor values, the bandwidth of a
CFB amplifier remains nearly constant with different gain
configurations.
When designing with CFB amplifiers always abide by these
basic rules:
• Use the recommended feedback resistor value
• Do not use reactive (capacitors, diodes, inductors, etc.)
elements in the direct feedback path
• Avoid stray or parasitic capacitance across feedback re-
sistors
• Follow general high-speed amplifier layout guidelines
• Ensure proper precautions have been made for driving
capacitive loads
©2007-2008 CADEKA Microcircuits LLC
Figure 1. Non-Inverting Gain Configuration with First
V
IN
R g
V
V
I err
OUT
IN
Order Transfer Function
= 1 +
x1
R
R
g
f
Z
o *I err
+
R
1 +
f
Z
1
o(jω)
R
V
f
OUT
Eq. 1
R
L
f
. By us-
CFB Technology - Theory of Operation
Figure 1 shows a simple representation of a current feed-
back amplifier that is configured in the traditional non-
inverting gain configuration.
Instead of having two high-impedance inputs similar to a
VFB amplifier, the inputs of a CFB amplifier are connected
across a unity gain buffer. This buffer has a high imped-
ance input and a low impedance output. It can source or
sink current (I
input to track the value of Vin. The CFB architecture em-
ploys a high gain trans-impedance stage that senses Ierr
and drives the output to a value of (Z
With the application of negative feedback, the amplifier
will drive the output to a voltage in a manner which tries
to drive Ierr to zero. In practice, primarily due to limita-
tions on the value of Z
finite value.
A closer look at the closed loop transfer function (Eq.1)
shows the effect of the trans-impedance, Z
gain of the circuit. At low frequencies where Z
large with respect to R
approaches unity, allowing R
higher frequencies, the value of Z
the effect of the secondary term will begin to dominate.
The -3dB small signal parameter specifies the frequency
where the value Z
gain to drop by 0.707 of the value at DC.
For more information regarding current feedback ampli-
fiers, visit www.cadeka.com for detailed application notes,
such as AN-3: The Ins and Outs of Current Feedback Am-
plifiers .
Figure 2. Inverting Gain Configuration with First Order
V
IN
V
R
V
OUT
IN
g
err
= −
) as needed to force the non-inverting
I err
o
(jω) equals the value of R
R
R
Transfer Function
g
f
f
, the second term of the equation
+
o
x1
(jω), Ierr remains a small but
1 +
Z
f
Z
o *I err
1
and R
o(jω)
R
f
R
f
o
(jω) will roll off, and
g
V
Eq. 2
to set the gain. At
o
www.cadeka.com
OUT
(jω) * I
o
f
o
(jω) on the
(jω) is very
causing the
err
R
) volts.
L
14