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CLC446AJ Schematic ( PDF Datasheet ) - National Semiconductor

Teilenummer CLC446AJ
Beschreibung 400MHz/ 50mW Current-Feedback Op Amp
Hersteller National Semiconductor
Logo National Semiconductor Logo 




Gesamt 12 Seiten
CLC446AJ Datasheet, Funktion
N
CLC446
400MHz, 50mW Current-Feedback Op Amp
November 1998
General Description
The National CLC446 is a very high-speed unity-gain-stable cur-
rent-feedback op amp that is designed to deliver the highest lev-
els of performance from a mere 50mW quiescent power. It pro-
vides a very wide 400MHz bandwidth, a 2000V/µs slew rate and
900ps rise/fall times. The CLC446 achieves its superior speed-
vs-power using an advanced complementary bipolar IC process
and National’s current-feedback architecture.
The CLC446 is designed to drive video loads with very low
differential gain and phase errors (0.02%, 0.03°). Combined with
its very low power (50mW), the CLC446 makes an excellent
choice for NTSC/PAL video switchers and routers. With its very
quick edge rates (900ps) and high slew rate (2000V/µs), the
CLC446 also makes an excellent choice for high-speed, high-
resolution component RGB video systems.
The CLC446 makes an excellent low-power high-resolution A/D
converter driver with its very fast 9ns settling time (to 0.1%) and
low harmonic distortion.
The combination of high performance and low power make
the CLC446 useful in many high-speed general purpose
applications. Its current-feedback architecture maintains consistent
performance over a wide gain range and signal levels. DC gain
and bandwidth can be set independently. Also, either maximally
flat AC response or linear phase response can be emphasized.
Features
s 400MHz bandwidth (Av = +2)
s 5mA supply current
s 0.02%, 0.03° differential gain, phase
s 2000V/µs slew rate
s 9ns settling to 0.1%
s 0.05dB gain flatness to 100MHz
s -65/-78dBc HD2/HD3
Applications
s High resolution video
s A/D driver
s Medical imaging
s Video switchers & routers
s RF/IF amplifier
s Communications
s Instrumentation
Non-Inverting
Frequency Response (Av = +2)
8
Vo = 0.5Vpp
6
4
2
0
-2
1M
10M 100M
Frequency (Hz)
1G
Typical Application
Elliptic-Function Low Pass Filter
R1 R2
C1
Vin +
C3 C4 C2 R4
CLC446
-
R3
Rg Rf
© 1998 National Semiconductor Corporation
Printed in the U.S.A.
Vo
R5
C5
Pinout
DIP & SOIC
VEE
VCC
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CLC446AJ Datasheet, Funktion
where
s = jω
( )τ1 = R1 R2 C1
τ2 = Rg C2
DC Design (DC offsets)
The DC offset model shown in Figure 6 is used to
calculate the output offset voltage. The equation for out-
put offset voltage is:
( ) ( )Vo = −
Vos + IBN Req1
1+
Rf
Req2
+
IBI Rf
The current offset terms, IBN and IBI , do not track each
other. The specifications are stated in terms of magni-
tude only. Therefore, the terms Vos, IBN, and IBI can have
either polarity. Matching the equivalent resistance seen
at both input pins does not reduce the output
offset voltage.
Req1
IBN
+
Vos
-
IBI
+
CLC446
-
Rf
Vo
RL
Req2
Figure 6: DC Offset Model
DC Design (output loading)
RL, Rf, and Rg load the op amp output. The equivalent
load seen by the output in Figure 6 is:
RL(eq) = RL || (Rf + Req2), non-inverting gain
RL(eq) = RL || Rf, inverting gain
RL(eq) needs to be large enough so that the minimum out-
put current can produce the required output voltage
swing.
AC Design (small signal bandwidth)
The CLC446 current-feedback amplifier bandwidth is
a function of the feedback resistor (Rf), not of the DC
voltage gain (AV). The bandwidth is approximately
1
proportional to Rf . As a rule, if Rf doubles, the band-
width is cut in half. Other AC specifications will also be
degraded. Decreasing Rf from the recommended value
increases peaking, and for very small values of Rf oscil-
lation will occur.
AC Design (minimum slew rate)
Slew rate influences the bandwidth of large signal
sinusoids. To determine an approximate value of slew
rate necessary to support a large sinusoid, use the
following equation:
SR 5 f Vpeak
where Vpeak is the peak output sinusoidal voltage.
The slew rate of the CLC446 in inverting gains is always
higher than in non-inverting gains.
AC Design (linear phase/constant group delay)
The recommended value of Rf produces minimal
peaking and a reasonably linear phase response.
To improve phase linearity when |Av| < 5, increase Rf
approximately 50% over its recommended value. Some
adjustment of Rf may be needed to achieve phase lin-
earity for your application. See the AC Design (small
signal bandwidth) sub-section for other effects of
changing Rf.
Propagation delay is approximately equal to group delay.
Group delay is related to phase by this equation:
τgd
=
(f)
=
1
360°
dφ(f)
df
∆φ(f)
f
where φ(f) is the phase in degrees. Linear phase implies
constant group delay. The technique for achieving linear
phase also produces a constant group delay.
AC Design (peaking)
Peaking is sometimes observed with the recommended
Rf. If a small increase in Rf does not solve the problem,
then investigate the possible causes and remedies
listed below.
s Capacitance across Rf
s Do not place a capacitor across Rf
s Use a resistor with low parasitic
capacitance for Rf
s A capacitive load
s Use a series resistor between the output and
a capacitive load (see the Recommended
Rs vs. CL plot)
s Long traces and/or lead lengths between Rf and
the CLC446
s Keep these traces as short as possible
For non-inverting and transimpedance gain configurations:
s Extra capacitance between the inverting pin
and ground (Cg)
s See the Printed Circuit Board Layout sub-
section below for suggestions on reducing Cg
s Increase Rf if peaking is still observed after
reducing Cg
For inverting gain configurations:
s Inadequate ground plane at the non-inverting pin
and/or long traces between non-inverting pin
and ground
s Place a 50 to 200resistor between the non-
inverting pin and ground (see Rt in Figure 2)
Capacitive Loads
Capacitive loads, such as found in A/D converters,
require a series resistor (Rs) in the output to
improve settling performance. The Recommended
Rs vs. CL plot in the Typical Performance
Characteristics section provides the information for
selecting this resistor.
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CLC446AJ pdf, datenblatt
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circuitry and specifications.
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