N
Comlinear CLC418
Dual High-Speed, Low-Power Line Driver
General Description
Features
The Comlinear CLC418 dual high-speed current-feedback
operational amplifier is designed to drive low-impedance and
high capacitance loads while maintaining high signal fidelity.
Operating on ±5V power supplies, each of the CLC418’s
amplifiers produces a continuous 96mA output current. Into a
back-terminated 50Ω load, the devices produce -85/-64dBc
second/third harmonic distortion (Av = +2, Vo = 2Vpp, f = 1MHz).
■
The CLC418’s current-feedback architecture maintains consistent
performance over a wide range of gain and signal levels. DC gain
and bandwidth can be set independently. With proper resistor
selection, either maximally flat gain response or linear phase
response can be selected.
Applications
■
■
■
■
■
■
■
■
■
■
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Requiring a mere 15mW quiescent power per amplifier, the
CLC418 offers superior performance-vs-power with a 130MHz
small-signal bandwidth, 350V/ms slew rate and quick 4.6ns
rise/fall times (2Vstep). The combination of low quiescent power,
high output current drive and high performance make the
CLC418 a great choice for many battery-powered personal
communication/computing systems.
■
■
■
130MHz bandwidth (Av = +2)
96mA output current
1.5mA supply current
-85/-75dBc HD2/HD3
15ns settling to 0.2%
-74dBc input-referred crosstalk (5MHz)
Single version available (CLC408)
ADSL/HDSL driver
Coaxial cable driver
UTP differential line driver
Transformer/coil driver
High capacitive-load driver
Video line driver
Portable/battery-powered line driver
Differential A/D driver
Comlinear CLC418
Dual High-Speed, Low-Power Line Driver
August 1996
Normalized Magnitude (1dB/div)
Non-Inverting Frequency Response
(Av = +2V/V, RL = 100Ω)
Combining the CLC418’s two amplifiers (shown below) results in
a powerful differential line driver for driving video signals over
unshielded twisted-pair (UTP). The CLC418 can also be used for
driving differential-input step-up transformers for applications
such as Asynchronous Digital Subscriber Lines (ADSL) or HighBit-Rate Digital Subscriber Lines (HDSL).
The CLC418’s amplifiers make excellent low-power highresolution A-to-D converter drivers with their very fast 15ns settling time (to 0.2%) and ultra-low -85/-75dBc harmonic distortion
(Av = +2, Vo = 2Vpp, f = 1MHz, RL = 1kΩ).
1M
100M
10M
Frequency (Hz)
418 Freq. Resp. Plot
Typical Application Diagram
Pinout
Differential Line Driver
with Load Impedance Conversion
DIP & SOIC
Rf2
Rg2
Vd/2
Vin
+
Rt1
1/2
CLC418
1/2
CLC418
Rf1
Rg1
-Vd/2
+
Rt2
Rm/2
Req
I:n
Io
Zo
RL
UTP
+
Vo
-
Rm/2
418 Typ App Diag
© 1996 National Semiconductor Corporation
Printed in the U.S.A.
Vo1
VCC
Vinv1
Vo2
Vnon-inv1
VEE
Vinv2
Vnon-inv2
418 Pinout
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CLC418 Electrical Characteristics (AV = +2, Rf = 1kΩ, Vcc = + 5V, RL = 100Ω, T = 25°C; unless specified)
PARAMETERS
Ambient Temperature
CONDITIONS
CLC418AJ
FREQUENCY DOMAIN RESPONSE
-3dB bandwidth
Vo < 1.0Vpp
Vo < 4.0Vpp
-0.1dB bandwidth
Vo < 1.0Vpp
gain flatness
Vo < 1.0Vpp
peaking
DC to 200MHz
rolloff
<30MHz
linear phase deviation
<30MHz
differential gain
NTSC, RL=150Ω
differential phase
NTSC, RL=150Ω
TIME DOMAIN RESPONSE
rise and fall time
settling time to 0.2%
overshoot
slew rate
AV = +2
2V step
2V step
2V step
2V step
DISTORTION AND NOISE RESPONSE
2Vpp, 1MHz
2nd harmonic distortion
2Vpp, 1MHz; RL = 1kΩ
2Vpp, 5MHz
3rd harmonic distortion
2Vpp, 1MHz
2Vpp, 1MHz; RL = 1kΩ
2Vpp, 5MHz
crosstalk (input-referred)
2Vpp, 5MHz
equivalent input noise
voltage (eni)
>1MHz
non-inverting current (ibn)
>1MHz
inverting current (ibi)
>1MHz
STATIC DC PERFORMANCE
input offset voltage
average drift
input bias current (non-inverting)
average drift
input bias current (inverting)
average drift
power supply rejection ratio
common-mode rejection ratio
supply current
DC
DC
RL= ∞, 2 channels
MISCELLANEOUS PERFORMANCE
input resistance (non-inverting)
input capacitance (non-inverting)
common mode input range
output voltage range
RL = 100Ω
output voltage range
RL = ∞
output current
output resistance, closed loop
DC
TYP
+25˚C
MIN/MAX RATINGS
+25˚C
0 to 70˚C -40 to 85˚C
UNITS
NOTES
130
45
30
80
33
25
80
29
20
75
28
20
MHz
MHz
MHz
B
0
0.2
0.2
0.1
0.4
0.5
0.45
0.4
–
–
0.9
0.6
0.5
–
–
1.0
0.6
0.5
–
–
dB
dB
deg
%
deg
B
B
4.6
15
5
350
7.0
30
12
260
7.5
38
12
225
8.0
40
12
215
ns
ns
%
V/µs
-85
-85
-65
-64
-75
-50
-74
–
–
-60
–
–
-45
-68
–
–
-58
–
–
-44
-68
–
–
-58
–
–
-44
-68
dBc
dBc
dBc
dBc
dBc
dBc
dBc
5
1.4
13
6.3
1.8
16
6.6
1.9
17
6.7
2.3
18
nV/√Hz
pA/√Hz
pA/√Hz
2
25
2
60
2
20
55
52
3.0
8
–
8
–
10
–
50
48
3.4
11
35
11
80
18
90
48
46
3.6
11
40
15
110
20
110
48
46
3.6
mV
µV/˚C
µA
nA/˚C
µA
nA/˚C
dB
dB
mA
5
1
±2.7
±3.3
±4.0
96
0.03
3
2
±2.3
±2.9
±3.8
96
0.15
2.5
2
±2.2
±2.8
±3.7
96
0.2
1
2
±2.0
±2.6
±3.5
60
0.3
MΩ
pF
V
V
V
mA
Ω
B
B
A
A
A
B
A
C
Min/max ratings are based on product characterization and simulation. Individual parameters are tested as noted. Outgoing quality levels are
determined from tested parameters.
Notes
Absolute Maximum Ratings
supply voltage
output current (see note C)
common-mode input voltage
maximum junction temperature
storage temperature range
lead temperature (soldering 10 sec)
ESD rating (human body model)
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A) J-level: spec is 100% tested at +25°C, sample tested at +85°C.
L-level: spec is 100% wafer probed at +25°C.
B) J-level: spec is sample tested at +25°C.
C) The output current sourced or sunk by the CLC418 can
exceed the maximum safe output current limit.
±7V
96mA
±VCC
+175°C
-65°C to +150°C
+300°C
4000V
2
Typical Performance Characteristics (A
v
Av+2
Gain
Av+1
Av+10
0
Av+10
Rf=200
-90
Av+5
Rf=402
-180
Av+2
Rf=953
Av+1
Rf=3k
-360
-450
100M
10M
Av-1
Gain
Av-10
Av-2
Phase
0
Av-5
Rf=301
1M
408 Plot1
Normalized Magnitude (1dB/div)
Magnitude (1dB/div)
1.0Vpp
2.0Vpp
4.0Vpp
+
Rs
-
CL
100M
10M
1k
CL=10pF
Rs =100
1M
-270
-360
-450
Channel A
Channel B
0
-135
-180
-225
20
180
Gain
140
Phase
10k
100
-
1k
Ii
10
CLC418
60
Vo
+
1M
10M
20
1k
100M
100k
10k
100
ibi
10
10
eni
Input-Referred Crosstalk
-40
1M
10M
1
100M
1k
100k
1M
10M
418 Plot8
2nd Harmonic Distortion, RL = 25Ω408 Plot9
-45
-20
Vo = 2Vpp
10MHz
-30
-60
-70
-50
-40
-50
2nd
RL = 100
3rd
RL = 100
-60
-70
3rd
RL = 1k
-80
-80
-90
Distortion (dBc)
Distortion (dBc)
-50
5MHz
-55
-60
2MHz
-65
1MHz
-70
2nd
RL = 1k
-75
-90
10M
100M
1M
Frequency (Hz)
10M
0
1
Frequency (Hz)
3rd Harmonic Distortion, RL = 25Ω418 Plot10
-50
1
100M
Frequency (Hz)
2nd & 3rd Harmonic Distortion
408 Plot7
Vo = 1Vpp
1M
10k
Frequency (Hz)
Frequency (Hz)
418 Plot6
ibn
100
0
100M
100
100Ω
100k
10M
Equivalent Input Noise
408 Plot5
1M
Magnitude (Ω)
PSRR
-90
Channel B
Noise Current (pA/√Hz)
30
-45
Channel A
Frequency (Hz)
Phase (deg)
CMRR
408 Plot3
Vo = 1Vpp
Frequency (Hz)
100k
100M
10M
1M
100M
10M
Open Loop Transimpedance Gain, Z(s)
408 Plot4
-90
-180
RL=25
Small Signal Channel Matching
CL= 1000pF
Rs =5.7
1k
10k
0
RL=1k
Frequency (Hz)
CL=100pF
Rs =24.9
1k
1k
RL=100
Phase
1M
CL=0pF
Rs =0
50
2
3
4
5
Output Amplitude (Vpp)
2nd Harmonic Distortion, RL = 100Ω
408 Plot10
-30
3rd Harmonic Distortion, RL = 100Ω
408 Plot11
-55
-40
Distortion (dBc)
-30
10MHz
-50
5MHz
-60
2MHz
-70
1MHz
-40
-60
Distortion (dBc)
PSRR/CMRR (dB)
-450
RL=100
Rf=1k
Phase (deg)
0.10Vpp
60
Distortion (dBc)
-360
Frequency Response vs. Capacitive Load
408 Plot2
Frequency (Hz)
-20
-270
100M
10M
Vo = 1Vpp
PSRR and CMRR
Crosstalk (dB)
Av-2
Rf=681
Av-1
Rf=806
RL=1k
Rf=1.21k
RL=25
Rf=0.95k
Gain
Frequency (Hz)
Frequency Response vs. Vout
40
-90
-180
Av-10
Rf=200
Frequency (Hz)
1M
Av-5
Vo = 1Vpp
Normalized Magnitude (1dB/div)
1M
-270
Vo = 1Vpp
Noise Voltage (nV/√Hz)
Phase
Phase (deg)
Av+5
Normalized Magnitude (1dB/div)
Vo = 1Vpp
Frequency Response vs. RL
Phase (deg)
Normalized Magnitude (1dB/div)
Inverting Frequency Response
Phase (deg)
Normalized Magnitude (1dB/div)
Non-Inverting Frequency Response
= +2, R f = 1kΩ, RL = 100Ω, VCC = + 5V, T = 25°C; CLC418AJ; unless specified)
10MHz
-65
-70
5MHz
-75
-80
2MHz
-85
1MHz
0
1
2
3
4
5
408 Plot12
2MHz
1MHz
-80
0
1
2
3
4
5
Output Amplitude (Vpp)
Output Amplitude (Vpp)
5MHz
-60
-70
-90
-80
10MHz
-50
3
0
1
2
3
4
5
Output Amplitude (Vpp)
408 Plot13
408 Plot14
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Typical Performance Characteristics (A
v
2nd Harmonic Distortion, RL = 1kΩ
3rd Harmonic Distortion, RL = 1kΩ
Closed Loop Output Resistance
-60
-55
100
10MHz
10MHz
-60
5MHz
-70
-75
2MHz
-80
1MHz
-85
Output Resistance (Ω)
-65
-65
-70
Distortion (dBc)
Distortion (dBc)
= +2, R f = 1kΩ, RL = 100Ω, VCC = + 5V, T = 25°C; CLC418AJ; unless specified)
5MHz
-75
-80
2MHz
-85
1MHz
-90
-90
-95
-95
0
1
2
3
4
2
1
3
4
5
10M
Output Amplitude (Vpp)
Output Amplitude (Vpp)
408 Plot16
Gain Flatness & Linear Phase Deviation
408 Plot15
Small Signal Pulse Response
Large Signal Pulse Response
Av+2
Av+2
0.10
0
Av-2
-0.10
2.0
0
-2.0
Av-2
-4.0
-0.20
1M
408 Plot17
4.0
Output Voltage
Output Voltage
Magnitude (0.1dB/div)
Phase Deviation (0.1°/div)
Gain
100M
Frequency (Hz)
0.20
Phase
1
0.1
0
5
10
Time (10ns/div)
Time (10ns/div)
10M
Frequency (Hz)
Short Term Settling Time
408 Plot18
Time (10ns/div)
0.4
0.1
0
-0.1
-0.2
0.2
0
-0.2
-0.4
0
40n
20n
60n
80n
1µ
100n
10µ
100µ
Time (s)
1m
IBI, 408
IBN, VPlot22
OS vs. Temperature
60
60
50
Offset Voltage VOS (mV)
Settling Time (ns)
30
Rs (Ω)
30
40
20
0.05%
20
10
3.0
6.0
5.0
IBI
2.5
4.0
2.0
3.0
1.5
2.0
IBN
IBI, IBN (µA)
40
1.0
0.1%
10
20p
100p
0
1000p
1.0
0
50
100
Temperature (°C)
408 Plot25
408 Plot24
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0.5
-50
CL (F)
4
100m
1
408 Plot23
3.5
7.0
VOS
Rs
10m
Time (s)
418
Settling Time
vs.Plot22
Capacitive Load
70
50
408 Plot21
Vout = 2Vstep
Vo (% Output Step)
Active Output Channel
Long Term Settling Time
408 Plot20
0.2
Vo (% Output Step)
Other Channel Output (20mV/div)
Active Channel Output (1V/div)
Pulse Crosstalk
CLC418 OPERATION
The CLC418 has a current-feedback (CFB) architecture
built in an advanced complementary bipolar process.
The key features of current-feedback are:
■
■
■
■
■
■
where:
■
■
■
AC bandwidth is independent of voltage gain
Inherently unity-gain stability
Frequency response may be adjusted with
feedback resistor (Rf in Figures 1-3)
High slew rate
Low variation in performance for a wide range
of gains, signal levels and loads
Fast settling
■
The denominator of the equation above is approximately
1 at low frequencies. Near the -3dB corner
frequency, the interaction between Rf and Z(jω)
dominates the circuit performance. Increasing Rf does
the following:
Current-feedback operation can be explained with a
simple model. The voltage gain for the circuits in Figures 1
and 2 is approximately:
Vo
=
Vin
Av is the DC voltage gain
Rf is the feedback resistor
Z(jω) is the CLC418’s open-loop
transimpedance gain
Z( jω )
is the loop gain
Rf
■
■
Av
Rf
1+
Z( jω )
■
■
■
Decreases loop gain
Decreases bandwidth
Reduces gain peaking
Lowers pulse response overshoot
Affects frequency response phase linearity
CLC418 DESIGN INFORMATION
The normalized gain plots in the Typical Performance
Characteristics section show different feedback
resistors (Rf) for different gains. These values of Rf are
recommended for obtaining the highest bandwidth with
minimal peaking. The resistor Rt provides DC bias for
the non-inverting input.
Standard op amp circuits work with CFB op amps. There
are 3 unique design considerations for CFB:
■
■
■
The feedback resistor (Rf in Figures 1-3) sets
AC performance
Rf cannot be replaced with a short or a capacitor
The output offset voltage is not reduced by
balancing input resistances
For Av < 6, use linear interpolation on the nearest Av
values to calculate the recommended value of Rf. For Av
≥ 6, the minimum recommended Rf is 200Ω.
The following sub-sections cover:
■
■
■
■
■
Design parameters, formulas and techniques
Interfaces
Application circuits
Layout techniques
SPICE model information
Select Rg to set the DC gain: R g =
Rf
Av − 1
DC gain accuracy is usually limited by the tolerance of Rf
and Rg.
DC Gain (non-inverting)
The non-inverting DC voltage gain for the configuration
R
A v = 1+ f
shown in Figure 1 is:
Rg
DC Gain (unity gain buffer)
The recommended Rf for unity gain buffers is 3kΩ. R g is
left open. Parasitic capacitance at the inverting node
may require a slight increase of Rf to maintain a flat
frequency response.
VCC
DC Gain (inverting)
The inverting DC voltage gain for the configuration
R
shown in Figure 2 is: A v = − f
Rg
6.8µF
+
Vin
3(5)
Rt
2(6)
+
8
1/2
CLC418
-
4
0.1µF
1(7)
Vo
The normalized gain plots in the Typical Performance
Characteristics section show different feedback
resistors (Rf) for different gains. These values of Rf are
recommended for obtaining the highest bandwidth with
minimal peaking. The resistor Rt provides DC bias for
the non-inverting input.
Rf
0.1µF
Rg
+
6.8µF
VEE
For |Av| < 6, use linear interpolation on the nearest Av
values to calculate the recommended value of Rf. For
|Av| ≥ 6, the minimum recommended Rf is 200Ω.
418 Fig1
Figure 1: Non-Inverting Gain
5
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VCC
Rt
6.8µF
+
+
Rt
3(5)
2(6)
Vin
0.1µF
8
+
Rg
-
Vo
1(7)
1/2
CLC418
Rg
Vref
Rref
Rf
4
Vo
1/2
CLC418
Vin
Rf
Figure 4: Level Shifting Circuit
418 Fig4
0.1µF
DC Design (DC offsets)
The DC offset model shown in Fig. 5 is used to calculate
the output offset voltage. The equation for output offset
voltage is:
Rf
Vo = − Vos + IBN ⋅ Req1 ⋅ 1 +
+ (IBI ⋅ R f )
Req2
+
6.8µF
VEE
(
418 Fig2
Figure 2: Inverting Gain
Rf
. At large gains,
Av
Rg becomes small and will load the previous stage. This
can be solved by driving Rg with a low impedance buffer
like the CLC111, or increasing Rf and Rg. See the
AC Design (small signal bandwidth) sub-section for
the tradeoffs.
Select Rg to set the DC gain: R g =
)
The current offset terms, IBN and IBI, do not track
each other. The specifications are stated in terms of
magnitude 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.
IBN
DC gain accuracy is usually limited by the tolerance of Rf
and Rg.
+
Vos
-
Req1
DC Gain (transimpedance)
Figure 3 shows a transimpedance circuit where the
current Iin is injected at the inverting node. The current
source’s output resistance is much greater than Rf.
RL(eq) =
6.8µF
+
2(6)
+
-
4
Vo
f
eq2
f
AC Design (small signal bandwidth)
The CLC418 current-feedback amplifier bandwidth is a
function of the feedback resistor (Rf), not of the DC voltage
gain (AV). The bandwidth is approximately proportional
Rf
+
6.8µF
to
VEE
418 Fig3
1
. As a rule, if Rf doubles, the bandwidth is cut in half.
Rf
Other AC specifications will also be degraded.
Decreasing Rf from the recommended value increases
peaking, and for very small values of Rf oscillation
will occur.
Figure 3: Transimpedance Gain
DC Design (level shifting)
Figure 4 shows a DC level shifting circuit for inverting
gain configurations. Vref produces a DC output level shift
R
of − Vref ⋅ f , which is independent of the DC output
Rref
produced by Vin.
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L
The equivalent output load (RL(eq)) needs to be large
enough so that the output current can produce the
required output voltage swing.
0.1µF
0.1µF
Iin
+ R ), non-inverting gain
{ RR |||| R(R, inverting
and transimpedance gain
L
1(7)
RL
DC Design (output loading)
RL, Rf, and Rg load the op amp output. The equivalent
load seen by the output in Figure 5 is:
VCC
1/2
CLC418
Rf
Figure 5: DC Offset Model
418 Fig5
DC gain accuracy is usually limited by the tolerance of Rf.
8
-
Req2
Vo
= −R f
Iin
The recommended Rf is 3kΩ. Parasitic capacitance at
the inverting node may require a slight increase of Rf to
maintain a flat frequency response.
3(5)
Vo
1/2
CLC418
IBI
The DC transimpedance gain is: AR =
Rt
+
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
6
following equation:
AC Design (crosstalk)
Crosstalk performance depends on the layout. Three
layout techniques that can reduce crosstalk are:
SR > 5 • f • Vpeak
where Vpeak is the peak output sinusoidal voltage.
■
Provide short symmetrical ground return paths for:
■ the inputs
■ the supply bypass capacitors
■ the load
■
Provide a short, grounded guard trace that:
■ goes underneath the package
■ is 0.1” (3mm) from the package pins
■ is on top and bottom of the printed circuit
board with connecting vias
■
Try different bypass capacitors to reduce high
frequency crosstalk
The slew rate of the CLC418 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| < 6, increase Rf approximately
50% over its recommended value. Some adjustment of
Rf may be needed to achieve phase linearity for your
application. See the AC Design (small signal bandwidth) sub-section for other effects of changing Rf.
The CLC418’s evaluation board was used to produce the
Input-Referred Crosstalk plot.
Propagation delay is approximately equal to group delay.
Group delay is related to phase by this equation:
τ gd (f) = −
Capacitive Loads
Capacitive loads, such as found in A/D converters,
require a series resistor (Rs) in the output to improve
settling performance. The Settling Time vs. Capacitive
Load plot in the Typical Performance Characteristics
section provides the information for selecting this resistor.
1 d φ(f)
1 ∆ φ( f )
⋅
≈−
⋅
360° d f
360° ∆ 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.
Using a resistor in series with a reactive load will also
reduce the load’s effect on amplifier loop dynamics. For
instance, driving coaxial cables without an output series
resistor may cause peaking or oscillation.
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:
■
■
■
Transmission Line Matching
One method for matching the characteristic impedance
of a transmission line is to place the appropriate
resistor at the input or output of the amplifier. Figure 6
shows the typical circuit configurations for matching
transmission lines.
Capacitance across Rf
■ Do not place a capacitor across Rf
■ Use a resistor with low parasitic
capacitance for Rf
A capacitive load
■ Use a series resistor between the output
and a capacitive load (see the Settling
Time versus CL plot)
Long traces and/or lead lengths between Rf
and the CLC418
■ Keep these traces as short as possible
R1
V1 +-
V2 +-
Z0
Rg
C6
+
1/2
CLC418
-
Z0
R6
Vo
R7
Rf
R5
Figure 6: Transmission Line Matching
418 Fig6
In non-inverting gain applications, Rg is connected
directly to ground. The resistors R1, R2, R6, and R7 are
equal to the characteristic impedance, Z o, of the
transmission line or cable. Use R3 to isolate the
amplifier from reactive loading caused by the transmission line, or by parasitics.
Extra capacitance between the inverting
pin and ground (Cg)
■ See the Printed Circuit Board Layout
sub-section below for suggestions on
reducing Cg
■ Increase R f if peaking is still observed
after reducing Cg
In inverting gain applications, R3 is connected directly to
ground. The resistors R4, R6, and R7 are equal to Zo. The
parallel combination of R5 and Rg is also equal to Zo.
For inverting gain configurations:
■
R3
R2
R4
For non-inverting and transimpedance gain configurations:
■
Z0
Inadequate ground plane at the non-inverting
pin and/or long traces between non-inverting
pin and ground
■ Place a 50 to 200Ω resistor between the
non-inverting pin and ground (see Rt in
Figure 2)
The input and output matching resistors attenuate the
signal by a factor of 2, therefore additional gain is needed.
Use C6 to match the output transmission line over a greater
frequency range. It compensates for the increase of
the op amps output impedance with frequency.
7
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Thermal Design
To calculate the power dissipation for the CLC418, follow
these steps for each individual amplifier:
Dynamic Range (noise)
The output noise defines the lower end of the CLC418’s
useful dynamic range. Reduce the value of resistors in
the circuit to reduce noise.
1) Calculate the no-load op amp power:
Pamp = ICC • (VCC – VEE)
2) Calculate the output stage’s RMS power:
Po = (VCC – Vload) • Iload , where Vload and Iload
are the RMS voltage and current across the
external load
3) Calculate the total op amp RMS power:
Pt = Pamp + Po
See the App Note Noise Design of CFB Op Amp
Circuits for more details. Our SPICE models support noise
simulations.
Dynamic Range (distortion)
The distortion plots in the Typical Performance
Characteristics section show distortion as a function
of load resistance, frequency, and output amplitude.
Distortion places an upper limit on the CLC418’s
dynamic range.
Now calculate the total power dissipated in the package:
4) Sum Pt for both op amps to obtain Ptot
To calculate the maximum allowable ambient temperature, solve the following equation: Tamb = 175 – Ptot • θJA,
where θJA is the thermal resistance from junction
to ambient in °C/W, and Tamb is in °C. The Package
Thermal Resistance section contains the thermal
resistance for various packages.
The CLC418’s output stage combines a voltage buffer
with a complementary common emitter current source.
The interaction between the buffer and the current
source produces a small amount of crossover distortion.
This distortion mechanism dominates at low output swing
and low resistance loads. To avoid this type of distortion,
use the CLC418 at high output swing.
Dynamic Range (input /output protection)
ESD diodes are present on all connected pins for protection from static voltage damage. For a signal that may
exceed the supply voltages, we recommend using diode
clamps at the amplifier’s input to limit the signals to less
than the supply voltages.
Realized output distortion is highly dependent upon the
external circuit. Some of the common external circuit
choices that can improve distortion are:
■
The CLC418’s output current can exceed the maximum
safe output current. To limit the output current to < 96mA:
■
■
■
Limit the output voltage swing with diode
clamps at the input
Vo(max)
Make sure that RL ≥
Io(max)
■
Short and equal return paths from the load to
the supplies
De-coupling capacitors of the correct value
Higher load resistance
Printed Circuit Board Layout
High frequency op amp performance is strongly dependent
on proper layout, proper resistive termination and
adequate power supply decoupling. The most important
layout points to follow are:
Vo(max) is the output voltage swing limit, and Io(max) is the
maximum safe output current.
Dynamic Range (input /output levels)
The Electrical Characteristics section specifies the
Common-Mode Input Range and Output Voltage
Range; these voltage ranges scale with the supplies.
Output Current is also specified in the Electrical
Characteristics section.
■
■
Use a ground plane
Bypass power supply pins with:
■
■
Unity gain applications are limited by the Common-Mode
Input Range. At greater non-inverting gains, the Output
Voltage Range becomes the limiting factor. Inverting
gain applications are limited by the Output Voltage
Range (and by the previous amplifier’s ability to drive
Rg). For transimpedance gain applications, the sum of
the input currents injected at the inverting input pin of
■
Vmax
, where Vmax is the
Rf
■
Output Voltage Range (see the DC Gain (transimpedance)
sub-section for details).
■
the op amp needs to be: Iin ≤
Minimize trace and lead lengths for components
between the inverting and output pins
Remove ground plane 0.1” (3mm) from all
input/output pads
For prototyping, use flush-mount printed circuit
board pins; never use high profile DIP sockets.
Evaluation Board
Separate evaluation boards are available for proto-typing
and measurements. Additional information is available in
the evaluation board literature.
The equivalent output load needs to be large enough
so that the minimum output current can produce the
required output voltage swing. See the DC Design
(output loading) sub-section for details.
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monolithic capacitors of about 0.1µF place
less than 0.1” (3mm) from the pin
tantalum capacitors of about 6.8µF for
large signal current swings or improved
power supply noise rejection;
we recommend a minimum of 2.2µF
for any circuit
8
SPICE Models
SPICE models provide a means to evaluate op amp
designs. Free SPICE models are available that:
■
■
■
Return Loss ≈ -20 ⋅ log10
n2 ⋅ Z o(418) (jω )
, dB
Zo
where Zo(418)(jω) is the output impedance of the CLC418,
and |Zo(418)(jω)| << Rm.
Support Berkeley SPICE 2G and its many
derivatives
Reproduce typical DC, AC, Transient, and
Noise performance
Support room temperature simulations
The load voltage and current will fall in the ranges:
Vo ≤ n ⋅ Vmax
The readme file that accompanies the models lists the
released models, and provides a list of modeled
parameters. The application note Simulation
SPICE Models for Comlinear’s Op Amps contains
schematics and detailed information.
Io ≤
Imax
n
The CLC418’s high output drive current and low
distortion make it a good choice for this application.
Lowpass Anti-aliasing Filter
with Delay Equalization
The circuit shown in Figure 7 is a 5th-order Butterworth
lowpass filter with group delay equalization. Vin needs to
be a voltage source with low output impedance. Section
A is a simple single-pole filter. Section B
provides a single-pole allpass function for group delay
equalization. Sections C and D are Sallen-Key lowpass
biquad sections.
CLC418 Applications
Differential Line Driver With Load
Impedance Conversion
The circuit shown in the Typical Application schematic
on the front page operates as a differential line driver.
The transformer converts the load impedance to
a value that best matches the CLC418’s output
capabilities. The single-ended input signal is
converted to a differential signal by the CLC418. The
line’s characteristic impedance is matched at both the
input and the output. The schematic shows Unshielded
Twisted Pair for the transmission line; other types of lines
can also be driven.
Vin
R1A
C2A
+
-
R1B
VoA
1/2
CLC418
U1A
+
RfA
VoB
1/2
CLC418
C2B
-
U1B
RfB
R3B
Set up the CLC418 as a difference amplifier:
R
Vd
R
= 2 ⋅ 1+ f1 = 2 ⋅ f2
Vin
R g2
R g1
C5C
R1C
Make the best use of the CLC418’s output drive
capability as follows:
Rm + Req
R3C
C4C
2 ⋅ Vmax
=
Imax
+
1/2
CLC418
-
C5D
R1D
αD
VoC
U2C
RfC
R1D
1- αD
R3D
C4D
+
1/2
CLC418
-
Vo
U2D
RfD
RgD
where Req is the transformed value of the load
impedance, Vmax is the Output Voltage Range, and Imax
is the maximum Output Current.
418 Fig7
Figure 7: Lowpass Anti-aliasing Filter
Match the line’s characteristic impedance:
The filter specifications we built to are:
RL = Z o
fc = 10MHz
(passband corner frequency)
Rm = Req
fs = 20MHz
(stopband corner frequency)
n=
Ap = 3.01dB (maximum passband attenuation)
RL
Req
Select the transformer so that it loads the line with a
value very near Zo over your frequency range. The output impedance of the CLC418 also affects the match.
With an ideal transformer we obtain:
As = 30dB
(minimum stopband attenuation)
Ho = 0dB
(DC gain)
The designed component values are in the table below.
The pre-distorted values compensate for the finite bandwidth of the CLC418.
9
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Component
R1A
C2A
RfA
R1B
C2B
R3B
RfB
R1C
R3C
C4C
C5C
RfC
R1D/αD
R1D/(1-αD)
R3D
C4D
C5D
RfD
RgD
Ideal
Value
Pre-distorted
For more information on the design of Sallen-Key filters and
filter pre-distortion, see Comlinear’s App Notes on filters.
211Ω
Precision Full-Wave Rectifier
Figure 9 shows a precision full-wave rectifier using the
CLC418. When Vin > 0, D1 is on, D2 is off, V2 = 0 and an
overall non-inverting gain is achieved. When Vin < 0, D1
is off, D2 is on, both V1 and V2 are positive, and an overall inverting gain is achieved. The output voltage of the
rectifier is:
238Ω
67pF
3.01kΩ
314Ω
67pF
953Ω
953Ω
108Ω
1.06kΩ
22pF
100pF
3.01kΩ
256Ω
256Ω
900Ω
22pF
100pF
953Ω
953Ω
300Ω
R 2 + R 5 + R7
R1
⋅ Vin ,Vin < 0
R2 + R5 R4
Vo = 1 +
⋅ 1+
R 3 R6
R R
2 ⋅ 7 ⋅ Vin ,Vin > 0
R1 R 5
100Ω
1.07kΩ
227Ω
227Ω
850Ω
R2
Vin
R1
+
The nearest standard values for capacitors and resistors
were used to build this filter. The resistors were 1%
tolerance, and the capacitors 5% tolerance. The ideal
and measured gains are shown in Figure 8.
Gain (dB)
U1b
R6
C1
Diodes D1 and D2 need to be Schottky or PIN diodes to
minimize delay.
-20
Select the voltage gain for U1a (G1 < 0) and U1b (G2).
G2 needs to be ≤ 1, approximately, to ensure realizable
values of R4. The overall gain is:
-30
Measured
-40
Vo
Ideal
-60
1
Vin
10
Frequency (MHz)
To change the cutoff frequency of this filter, do the following:
Set R7 to the recommended feedback resistor value for
the gain Av = (1 + G2).
Determine the new cutoff frequency:
f3dB(418)
, where f3dB(418) is the
fc(new) ≤
10
bandwidth of the CLC418
Calculate the ratio:
Scale (multiply) all frequency specifications and
plot axes by fc(new)/fc
Make sure that your system requirements are met
Scale (multiply) all capacitor values by fc/fc(new)
Set the resistors to the Ideal Values in the table
above (the pre-distorted values do not linearly
scale with frequency)
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= G1G2 , Vin > 0
Set R2 = R3 to the recommended feedback resistor
value for the gain Av = R2. You may need to increase R2
and R3 slightly to compensate for the delays through D1
and D2.
Fig8
Figure 8: Lowpass Anti-aliasing Filter418
Response
■
+
Vo
Figure 9: Precision Full-Wave Rectifier418 Fig9
-50
■
1/2
CLC418
R4
V2
-10
■
-
D2
U1a
R3
R7
20Ω
0
■
R5
D1
1/2
CLC418
Table 1: Filter Component Values
■
V1
1+
R4
=
R6
R7
R2
R7
1 R2
1 + G − 1 + R G2 − R
2
3
3
R7 R 2
⋅ G2
+
R3 R3
If this ratio is negative, reduce G2 and recalculate the
values up to this point.
10
Calculate all other resistor values:
R1 =
R2
G1
R5 =
R7
G2
R6 =
We built and tested a full-wave rectifier with the
following values:
■
■
■
R5
■
R4
1+ R
6
■
■
R 4 = R 5 − R6
D1 = D2 = Schottky Diodes,
Digi-Key # SD101ACT-ND
R2 = R3 = R7 = 1.00kΩ
R1 = 1.00kΩ
R5 = 1.50kΩ
R6 = 882Ω
R4 = 618Ω
The rectifier had equal inverting and non-inverting gains
for frequencies less than 10MHz. The -3dB bandwidth
was about 25MHz.
Notice that R4 and R6 are selected so that U1a and the
diodes see a balanced load for both polarities of Vin.
The capacitor C 1 is optional. It helps compensate for the
difference between the gains Vo/V1 and Vo/V2 at high
frequencies. Both R4 and R6 must be > 0.
Package Thermal Resistance
Ordering Information
Model
CLC418AJP
CLC418AJE
CLC418AJE-TR
CLC418AJE-TR13
CLC418ALC
Temperature Range
Description
-40˚C to +85 ˚C
-40˚C to +85 ˚C
-40˚C to +85 ˚C
-40˚C to +85 ˚C
-40˚C to +85 ˚C
8-pin PDIP
8-pin SOIC
8-pin SOIC, 750pc reel
8-pin SOIC, 2500pc reel
dice (commercial)
qJC
qJA
80˚C/W
95˚C/W
95˚C/W
115˚C/W
Package
Plastic (AJP)
Surface Mount (AJE)
Reliability Information
Transistor Count
MTBF (based on limited test data)
11
76
34Mhr
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Comlinear CLC418
Dual High-Speed, Low-Power Line Driver
Customer Design Applications Support
National Semiconductor is committed to design excellence. For sales, literature and technical support, call the
National Semiconductor Customer Response Group at 1-800-272-9959 or fax 1-800-737-7018.
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National’s products are not authorized for use as critical components in life support devices or systems without the express written approval
of the president of National Semiconductor Corporation. As used herein:
1. Life support devices or systems are devices or systems which, a) are intended for surgical implant into the body, or b) support or
sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can
be reasonably expected to result in a significant injury to the user.
2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to
cause the failure of the life support device or system, or to affect its safety or effectiveness.
N
National Semiconductor
Corporation
National Semiconductor
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National Semiconductor
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circuitry and specifications.
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12
Lit #150418-003