NSC LM13600M, LM13600AN, LM13600N Datasheet
LM13600
Dual Operational Transconductance Amplifiers with
Linearizing Diodes and Buffers
General Description
The LM13600 series consists of two current controlled
transconductance amplifiers each with differential inputs and
a push-pull output. The two amplifiers share common supplies but otherwise operate independently. Linearizing diodes are providedattheinputs to reduce distortion and allow
higher input levels. The result is a 10 dB signal-to-noise improvement referenced to 0.5 percent THD. Controlled impedance buffers which are especially designed to complement the dynamic range of the amplifiers are provided.
Features
n gmadjustable over 6 decades
n Excellent g
linearity
m
Connection Diagram
Dual-In-Line and Small Outline Packages
n Excellent matching between amplifiers
n Linearizing diodes
n Controlled impedance buffers
n High output signal-to-noise ratio
Applications
n Current-controlled amplifiers
n Current-controlled impedances
n Current-controlled filters
n Current-controlled oscillators
n Multiplexers
n Timers
n Sample and hold circuits
LM13600 Dual Operational Transconductance Amplifiers with Linearizing Diodes and Buffers
May 1998
DS007980-2
Order Number LM13600M, LM13600N or LM13600AN
See NS Package Number M16A or N16A
© 1999 National Semiconductor Corporation DS007980 www.national.com
Top View
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (Note 2)
LM13600 36 V
LM13600A 44 V
=
Power Dissipation (Note 3) T
25˚C 570 mW
A
Differential Input Voltage
Diode Bias Current (I
Amplifier Bias Current (I
)2mA
D
)2mA
ABC
Output Short Circuit Duration Continuous
DC
DC
or±18V
or±22V
±
Operating Temperature Range 0˚C to +70˚C
DC Input Voltage +V
Storage Temperature Range −65˚C to +150˚C
Soldering Information
Dual-In-Line Package
Soldering (10 seconds) 260˚C
Small Outline Package
Vapor Phase (60 seconds) 215˚C
5V
Infrared (15 seconds) 220˚C
See AN-450 “Surface Mounting Methods and Their Effect
on Product Reliability” for other methods of soldering
surface mount devices.
S
to −V
Buffer Output Current (Note 4) 20 mA
Electrical Characteristics (Note 5)
Parameter Conditions LM13600 LM13600A Units
Min Typ Max Min Typ Max
Input Offset Voltage (V
V
Including Diodes Diode Bias Current (ID)=500 µA 0.5 5 0.5 2 mV
OS
Input Offset Change 5 µA ≤ I
Input Offset Current 0.1 0.6 0.1 0.6 µA
Input Bias Current 0.4 5 0.4 5 µA
Forward
Transconductance (g
g
Tracking 0.3 0.3 dB
m
Peak Output Current R
Peak Output Voltage
Positive R
Negative R
Supply Current I
V
Sensitivity
OS
Positive ∆ V
Negative ∆ V
CMRR 80 110 80 110 dB
Common Mode Range
Crosstalk Referred to Input (Note 6) 100 100 dB
Differential Input Current I
Leakage Current I
Input Resistance 10 26 10 26 kΩ
Open Loop Bandwidth 2 2 MHz
Slew Rate Unity Gain Compensated 50 50 V/µs
Buffer Input Current (Note 6), Except I
Peak Buffer Output Voltage (Note 6) 10 10 V
) 0.4 4 0.4 1 mV
OS
Over Specified Temperature Range 2 mV
=
I
5 µA 0.3 4 0.3 1 mV
ABC
≤ 500 µA 0.1 3 0.1 1 mV
ABC
Over Specified Temperature Range 1 8 1 7 µA
) 6700 9600 13000 7700 9600 12000 µmho
m
Over Specified Temperature Range 5400 4000 µmho
=
L
=
R
L
=
R
L
Range
=
L
=
L
ABC
OS
OS
20 Hz
ABC
ABC
=
0, I
0, I
0, Over Specified Temp
∞
∞
=
5µA 5 3 5 7 µA
ABC
=
500 µA 350 500 650 350 500 650 µA
ABC
300 300 µA
,5µA≤I
,5µA≤I
≤ 500 µA +12 +14.2 +12 +14.2 V
ABC
≤ 500 µA −12 −14.4 −12 −14.4 V
ABC
500 µA, Both Channels 2.6 2.6 mA
/∆V+ 20 150 20 150 µV/V
/∆V− 20 150 20 150 µV/V
±12±
13.5
<f<
20 kHz
=
=
=
±
0, Input
4V 0.02 100 0.02 10 nA
0 (Refer to Test Circuit) 0.2 100 0.2 5 nA
=
0 µA 0.2 0.4 0.2 0.4 µA
ABC
±12±
13.5 V
S
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Electrical Characteristics (Note 5) (Continued)
Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is
functional, but do not guarantee specific performance limits.
Note 2: For selections to a supply voltage above
Note 3: For operating at high temperatures, the device must be derated based on a 150˚C maximum junction temperature and a thermal resistance of 175˚C/W
which applies for the device soldered in a printed circuit board, operating in still air.
Note 4: Buffer output current should be limited so as to not exceed package dissipation.
Note 5: These specifications apply for V
the buffers are grounded and outputs are open.
Note 6: These specifications apply for V
to the transconductance amplifier output.
=
±
S
=
±
S
±
22V, contact factory.
=
15V,T
25˚C, amplifier bias current (I
A
=
15V, I
ABC
500 µA, R
)=500 µA, pins 2 and 15 open unless otherwise specified. The inputs to
ABC
=
5kΩconnected from the buffer output to −V
OUT
and the input of the buffer is connected
S
Schematic Diagram
One Operational Transconductance Amplifier
Typical Performance Characteristics
Input Offset Voltage
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Input Offset Current
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Input Bias Current
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Typical Performance Characteristics (Continued)
Peak Output Current
Input Leakage
Amplifier Bias Voltage vs
Amplifier Bias Current
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Peak Output Voltage and
Common Mode Range
Transconductance
Input and Output Capacitance
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Leakage Current
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Input Resistance
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Output Resistance
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Typical Performance Characteristics (Continued)
Distortion vs Differential
Input Voltage
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Voltage vs Amplifier Bias Current
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Unity Gain Follower
Output Noise vs Frequency
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Leakage Current Test Circuit
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Differential Input Current Test Circuit
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Circuit Description
The differential transistor pair Q4and Q5form a transconductance stage in that the ratio of their collector currents is
defined by the differential input voltage according to the
transfer function:
(1)
where V
mately 26 mV at 25˚C and I
of transistors Q
Q
Transistors Q
which forces the sum of currents I
where I
pin.
For small differential input voltages the ratio of I
proaches unity and the Taylorseries of the In function can be
approximated as:
is the differential input voltage, kT/q is approxi-
IN
and Q4respectively. With the exception of
and Q13, all transistors and diodes are identical in size.
3
5
and Q2with Diode D1form a current mirror
1
is the amplifier bias current applied to the gain
ABC
and I4are the collector currents
5
and I5to equal I
4
=
I
I
4+I5
ABC
ABC
and I5ap-
4
;
(2)
(3)
(5)
The term in brackets is then the transconductance of the amplifier and is proportional to I
ABC
.
Linearizing Diodes
For differential voltages greater than a few millivolts,
tion (3)
becomes less valid and the transconductance be-
comes increasingly nonlinear.
Figure 1
demonstrates how
the internal diodes can linearize the transfer function of the
amplifier. For convenience assume the diodes are biased
with current sources and the input signal is in the form of current I
. Since the sum of I4and I5is I
S
is I
, currents I4and I5can be written as follows:
OUT
and the difference
ABC
Since the diodes and the input transistors have identical geometries and are subject to similar voltages and temperatures, the following is true:
Equa-
(4)
Collector currents I
and it is necessary to subtract one current from the other.
and I5are not very useful by themselves
4
The remaining transistors and diodes form three current mirrors that produce an output current equal to I
minus I4thus:
5
FIGURE 1. Linearizing Diodes
(6)
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Linearizing Diodes (Continued)
Notice that in deriving Equation 6 no approximations have
been made and there are no temperature-dependent terms.
The limitations are that the signal current not exceed I
and that the diodes be biased with currents. In practice, re-
D
placing the current sources with resistors will generate insignificant errors.
Controlled Impedance Buffers
The upper limit of transconductance is defined by the maximum value of I
the amplifier will function therefore determines the overall
dynamic range. At very low values of I
very low input bias current is desirable. An FET follower satisfies the low input current requirement, but is somewhat
non-linear for large voltage swing. The controlled impedance
buffer is a Darlington which modifies its input bias current to
suit the need. For low values of I
rent is minimal. At higher levels of I
up Q
with a current proportional to I
12
When I
ABC
buffer will shift. In audio applications where I
suddenly, this shift may produce an audible “pop”. For these
applications the LM13700 may produce superior results.
(2 mA). The lowest value of I
ABC
, a buffer which has
ABC
, the buffer’s input cur-
ABC
, transistor Q3biases
ABC
is changed, the DC level of the Darlington output
ABC
for which
ABC
for fast slew rate.
is changed
ABC
Applications-Voltage Controlled
Amplifiers
Figure 2
/2
shows how the linearizing diodes can be used in a
voltage-controlled amplifier. To understand the input biasing,
it is best to consider the 13 kΩ resistor as a current source
and use a Thevenin equivalent circuit as shown in
This circuit is similar to
potentiometer in
Figure 1
Figure 2
and operates the same. The
is adjusted to minimize the effects
Figure 3
of the control signal at the output.
For optimum signal-to-noise performance, I
large as possible as shown by the Output Voltage vs. Ampli-
should be as
ABC
fier Bias Current graph. Larger amplitudes of input signal
also improve the S/N ratio. The linearizing diodes help here
by allowing larger input signals for the same output distortion
as shown by the Distortion vs. Differential Input Voltage
graph. S/N may be optimized by adjusting the magnitude of
the input signal via R
below some desired level. The output voltage swing can
then be set at any level by selecting R
(
IN
Figure 2
) until the output distortion is
.
L
Although the noise contribution of the linearizing diodes is
negligible relative to the contribution of the amplifier’s internal transistors, I
mizes the dynamic junction resistance of the diodes (r
maximizes their linearizing action when balanced against
R
. A value of 1 mA is recommended for IDunless the spe-
IN
cific application demands otherwise.
should be as large as possible. This mini-
D
) and
e
.
FIGURE 2. Voltage Controlled Amplifier
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Applications-Voltage Controlled Amplifiers (Continued)
FIGURE 3. Equivalent VCA Input Circuit
Stereo Volume Control
The circuit of
LM13600 amplifiers to provide a Stereo VolumeControl with
a typical channel-to-channel gain tracking of 0.3 dB. R
provided to minimize the output offset voltage and may be
replaced with two 510Ω resistors in AC-coupled applications.
For the component values given, amplifier gain is derived for
Figure 2
Figure 4
as being:
uses the excellent matching of the two
P
If VCis derived from a second signal source then the circuit
becomes an amplitude modulator or two-quadrant multiplier
as shown in
Figure 5
is
DS007980-10
, where:
FIGURE 4. Stereo Volume Control
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DS007980-11
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