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LM13700
Dual Operational Transconductance Amplifiers with
Linearizing Diodes and Buffers
LM13700 Dual Operational Transconductance Amplifiers with Linearizing Diodes and Buffers
August 2000
General Description
The LM13700 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.Linearizingdiodes are providedattheinputstoreduce distortion and allow
higher input levels. The result is a 10 dB signal-to-noise improvement referenced to 0.5 percent THD. High impedance
buffers are provided which are especially designed to
complement the dynamic range of the amplifiers. The output
buffers of the LM13700 differ from those of the LM13600 in
that their input bias currents (and hence their output DC levels) are independent of I
superior to that of the LM13600 in audio applications.
. This may result in performance
ABC
Features
n gmadjustable over 6 decades
Connection Diagram
Dual-In-Line and Small Outline Packages
n Excellent g
n Excellent matching between amplifiers
n Linearizing diodes
n High impedance buffers
n High output signal-to-noise ratio
linearity
m
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
DS007981-2
Top View
Order Number LM13700M, LM13700MX or LM13700N
See NS Package Number M16A or N16A
© 2000 National Semiconductor Corporation DS007981 www.national.com
Page 2
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
LM13700
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (Note 2)
LM13700 36 V
Power Dissipation (Note 3) T
LM13700N 570 mW
Differential Input Voltage
Diode Bias Current (I
)2mA
D
Amplifier Bias Current (I
Output Short Circuit Duration Continuous
= 25˚C
A
)2mA
ABC
DC
or±18V
±
5V
Operating Temperature Range
LM13700N 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 sec.) 260˚C
Small Outline Package
Vapor Phase (60 sec.) 215˚C
Infrared (15 sec.) 220˚C
See AN-450 “Surface Mounting Methods and Their Effect
on Product Reliability” for other methods of soldering
surface mount devices.
Buffer Output Current (Note 4) 20 mA
Electrical Characteristics (Note 5)
Parameter Conditions
Input Offset Voltage (V
) 0.4 4
OS
Min Typ Max
Over Specified Temperature Range mV
I
= 5 µA 0.3 4
ABC
V
Including Diodes Diode Bias Current (ID) = 500 µA 0.5 5 mV
OS
Input Offset Change 5 µA ≤ I
≤ 500 µA 0.1 3 mV
ABC
Input Offset Current 0.1 0.6 µA
Input Bias Current Over Specified Temperature Range 0.4 5 µA
Forward 6700 9600 13000 µmho
Transconductance (g
g
Tracking 0.3 dB
m
Peak Output Current R
) Over Specified Temperature Range 5400
m
=0,I
L
R
=0,I
L
R
= 0, Over Specified Temp Range 300
L
= 5 µA 5
ABC
= 500 µA 350 500 650 µA
ABC
Peak Output Voltage
Positive R
Negative R
Supply Current I
V
Sensitivity
OS
Positive ∆V
Negative ∆V
=∞,5µA≤I
L
=∞,5µA≤I
L
= 500 µA, Both Channels 2.6 mA
ABC
+
/∆V
OS
−
/∆V
OS
≤ 500 µA +12 +14.2 V
ABC
≤ 500 µA −12 −14.4 V
ABC
CMRR 80 110 dB
Common Mode Range
±
12
Crosstalk Referred to Input (Note 6) 100 dB
<f<
Differential Input Current I
Leakage Current I
20 Hz
= 0, Input =±4V 0.02 100 nA
ABC
= 0 (Refer to Test Circuit) 0.2 100 nA
ABC
20 kHz
Input Resistance 10 26 kΩ
Open Loop Bandwidth 2 MHz
Slew Rate Unity Gain Compensated 50 V/µs
Buffer Input Current (Note 6) 0.5 2 µA
Peak Buffer Output Voltage (Note 6) 10 V
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
±
22V, contact factory.
LM13700
18
20 150 µV/V
20 150 µV/V
±
13.5 V
S
to −V
Units
S
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Page 3
Electrical Characteristics (Note 5) (Continued)
Note 3: For operation at ambient temperatures above 25˚C, the device must be derated based on a 150˚C maximum junction temperature and a thermal resistance,
junction to ambient, as follows: LM13700N, 90˚C/W; LM13700M, 110˚C/W.
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.
=±15V,TA= 25˚C, amplifier bias current (I
S
=±15V, I
S
= 500 µA, R
ABC
=5kΩconnected from the buffer output to −VSand the input of the buffer is connected
OUT
) = 500 µA, pins 2 and 15 open unless otherwise specified. The inputs to
ABC
Schematic Diagram
One Operational Transconductance Amplifier
LM13700
Typical Application
DS007981-1
DS007981-18
Voltage Controlled Low-Pass Filter
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Page 4
Typical Performance Characteristics
Input Offset Voltage
LM13700
Peak Output Current
DS007981-38
Input Offset Current
Peak Output Voltage and
Common Mode Range
DS007981-39
Input Bias Current
DS007981-40
Leakage Current
Input Leakage
Amplifier Bias Voltage vs
Amplifier Bias Current
DS007981-41
DS007981-44
DS007981-42
Transconductance
DS007981-45
Input and Output Capacitance
DS007981-43
Input Resistance
DS007981-46
Output Resistance
DS007981-47
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DS007981-48
DS007981-49
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Typical Performance Characteristics (Continued)
LM13700
Distortion vs Differential
Input Voltage
DS007981-50
Voltage vs Amplifier
Bias Current
Unity Gain Follower
Output Noise vs Frequency
DS007981-52
DS007981-51
Leakage Current Test Circuit
DS007981-6
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:
Differential Input Current Test Circuit
where V
mately 26 mV at 25˚C and I
of transistors Q
is the differential input voltage, kT/q is approxi-
IN
and Q4respectively. With the exception of
5
and I4are the collector currents
5
DS007981-5
DS007981-7
(1)
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Page 6
Circuit Description (Continued)
Q
and Q13, all transistors and diodes are identical in size.
3
LM13700
Transistors Q
which forces the sum of currents I
where I
and Q2with Diode D1form a current mirror
1
I
4+I5=IABC
is the amplifier bias current applied to the gain
ABC
and I5to equal I
4
pin.
For small differential input voltages the ratio of I
proaches unity and the Taylorseries of the In function can be
approximated as:
Collector currents I
and I5are not very useful by themselves
4
and it is necessary to subtract one current from the other.
The remaining transistors and diodes form three current mirrors that produce an output current equal to I
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)
comes increasingly nonlinear.
the internal diodes can linearize the transfer function of the
becomes less valid and the transconductance be-
Figure 1
demonstrates how
:
ABC
(2)
and I5ap-
4
(3)
(4)
minus I4thus:
(5)
Equa-
amplifier. For convenience assume the diodes are biased
with current sources and the input signal is in the form of cur-
. Since the sum of I4and I5is I
rent 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:
(6)
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
D
and that the diodes be biased with currents. In practice, replacing the current sources with resistors will generate insignificant errors.
Applications:
Voltage Controlled Amplifiers
Figure 2
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
of the control signal at the output.
shows how the linearizing diodes can be used in a
Figure 3
Figure 1
Figure 2
and operates the same. The
is adjusted to minimize the effects
/2
.
FIGURE 1. Linearizing Diodes
For optimum signal-to-noise performance, I
should be as
ABC
large as possible as shown by the Output Voltage vs. Amplifier 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
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DS007981-8
the input signal via R
(
IN
Figure 2
) until the output distortion is
below some desired level. The output voltage swing can
then be set at any level by selecting R
.
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
should be as large as possible. This mini-
D
e
) and
Page 7
Applications:
Voltage Controlled Amplifiers
(Continued)
maximizes their linearizing action when balanced against
R
. A value of 1 mA is recommended for IDunless the spe-
IN
cific application demands otherwise.
LM13700
FIGURE 2. Voltage Controlled Amplifier
FIGURE 3. Equivalent VCA Input Circuit
Stereo Volume Control
The circuit of
LM13700 amplifiers to provide a Stereo Volume Control 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
DS007981-9
DS007981-10
If VCis derived from a second signal source then the circuit
becomes an amplitude modulator or two-quadrant multiplier
as shown in
Figure 5
, where:
is
The constant term in the above equation may be cancelled
by feeding I
ure 6
SxIDRC
adds RMto provide this current, resulting in a
four-quadrant multiplier where R
0V for V
=0V.RMalso serves as the load resistor for IO.
IN2
/2(V− + 1.4V) into IO. The circuit of
is trimmed such that VO=
C
Fig-
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Page 8
Stereo Volume Control (Continued)
LM13700
DS007981-11
FIGURE 4. Stereo Volume Control
FIGURE 5. Amplitude Modulator
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DS007981-12
Page 9
Stereo Volume Control (Continued)
FIGURE 6. Four-Quadrant Multiplier
Noting that the gain of the LM13700 amplifier of
Figure 3
may be controlled by varying the linearizing diode current I
as well as by varying I
using this approach. As V
(3V
) to turn on the Darlington transistors and the lineariz-
BE
ing diodes, the increase in I
as to hold V
at that level.
O
,
Figure 7
ABC
reaches a high enough amplitude
O
shows an AGC Amplifier
reduces the amplifier gain so
D
Voltage Controlled Resistors
An Operational Transconductance Amplifier (OTA) may be
used to implement a Voltage Controlled Resistor as shown in
Figure 8
the LM13700 which is then multiplied by the g
fier to produce an output current, thus:
. A signal voltage applied at RXgenerates a VINto
of the ampli-
m
LM13700
DS007981-13
D
where gm≈ 19.2I
by R and RAis necessary to maintain VINwithin the linear
range of the LM13700 input.
Figure 9
shows a similar VCR where the linearizing diodes
are added, essentially improving the noise performance of
the resistor. A floating VCR is shown in
each “end” of the “resistor” may be at any voltage within the
output voltage range of the LM13700.
at 25˚C. Note that the attenuation of V
ABC
Figure 10
O
, where
FIGURE 7. AGC Amplifier
DS007981-14
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Page 10
Voltage Controlled Resistors (Continued)
LM13700
FIGURE 8. Voltage Controlled Resistor, Single-Ended
DS007981-15
FIGURE 9. Voltage Controlled Resistor with Linearizing Diodes
Voltage Controlled Filters
OTA’s are extremely useful for implementing voltage controlled filters, with the LM13700 having the advantage that
the required buffers are included on the I.C. The VC Lo-Pass
Filter of
Figure 11
frequencies below cut-off, with the cut-off frequency being
the point at which X
R
).At frequencies above cut-off the circuit provides a single
A
RC roll-off (6 dB per octave) of the input signal amplitude
with a −3 dB point defined by the given equation, where g
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performs as a unity-gain buffer amplifier at
equals the closed-loop gain of (R/
C/gm
m
DS007981-16
is again 19.2 x I
at room temperature.
ABC
Figure 12
shows a
VC High-Pass Filter which operates in much the same manner, providing a single RC roll-off below the defined cut-off
frequency.
Additional amplifiers may be used to implement higher order
filters as demonstrated by the two-pole Butterworth Lo-Pass
Filter of
Due to the excellent g
Figure 13
and the state variable filter of
tracking of the two amplifiers, these
m
Figure 14
filters perform well over several decades of frequency.
.
Page 11
Voltage Controlled Filters (Continued)
FIGURE 10. Floating Voltage Controlled Resistor
LM13700
DS007981-17
FIGURE 11. Voltage Controlled Low-Pass Filter
DS007981-18
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Page 12
Voltage Controlled Filters (Continued)
LM13700
FIGURE 12. Voltage Controlled Hi-Pass Filter
DS007981-19
FIGURE 13. Voltage Controlled 2-Pole Butterworth Lo-Pass Filter
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DS007981-20
Page 13
Voltage Controlled Filters (Continued)
FIGURE 14. Voltage Controlled State Variable Filter
Voltage Controlled Oscillators
The classic Triangular/Square Wave VCO of
one of a variety of Voltage Controlled Oscillators which may
be built utilizing the LM13700. With the component values
shown, this oscillator provides signals from 200 kHz to below
2HzasI
tudes are set by I
is varied from 1 mA to 10 nA. The output ampli-
C
. Note that the peak differential input
AxRA
voltage must be less than 5V to prevent zenering the inputs.
A few modifications to this circuit produce the ramp/pulse
VCO of
Figure 16
. When VO2is high, IFis added to ICto increase amplifier A1’s bias current and thus to increase the
charging rate of capacitor C. When V
O2
zero and the capacitor discharge current is set by I
Figure 15
is low, IFgoes to
.
C
LM13700
DS007981-21
The VC Lo-Pass Filter of
is
a high-quality sinusoidal VCO. The circuit of
ploys two LM13700 packages, with three of the amplifiers
Figure 11
configured as lo-pass filters and the fourth as a limiter/
inverter. The circuit oscillates at the frequency at which the
loop phase-shift is 360˚ or 180˚ for the inverter and 60˚ per
filter stage. This VCO operates from 5 Hz to 50 kHz with less
than 1% THD.
may be used to produce
Figure 16
em-
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Page 14
Voltage Controlled Oscillators (Continued)
LM13700
DS007981-22
FIGURE 15. Triangular/Square-Wave VCO
DS007981-23
FIGURE 16. Ramp/Pulse VCO
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Page 15
Voltage Controlled Oscillators (Continued)
LM13700
Figure 18
amplifier is needed for another function.
shows how to build a VCO using one amplifier when the other
FIGURE 18. Single Amplifier VCO
FIGURE 17. Sinusoidal VCO
Additional Applications
Figure 19
power supply current until it is triggered.A positive-going trigger pulse of at least 2V amplitude turns on the amplifier
through R
fier regenerates and latches its output high until capacitor C
charges to the voltage level on the non-inverting input. The
output then switches low, turning off the amplifier and discharging the capacitor. The capacitor discharge rate is
speeded up by shorting the diode bias pin to the inverting input so that an additional discharge current flows through D
DS007981-25
when the amplifier output switches low. A special feature of
this timer is that the other amplifier, when biased from V
can perform another function and draw zero stand-by power
as well.
DS007981-24
presents an interesting one-shot which draws no
and pulls the non-inverting input high. The ampli-
B
I
,
O
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Page 16
Additional Applications (Continued)
LM13700
FIGURE 19. Zero Stand-By Power Timer
The operation of the multiplexer of
forward. When A1 is turned on it holds V
when A2 is supplied with bias current then it controls V
and RCserve to stabilize the unity-gain configuration of amplifiers A1 and A2. The maximum clock rate is limited to
about 200 kHz by the LM13700 slew rate into 150 pF when
the (V
IN1–VIN2
) differential is at its maximum allowable value
of 5V.
Figure 20
O
is very straight-
equal to V
IN1
O.CC
and
The Phase-Locked Loop of
multiplier of
PLL with a
Figure 6
±
and the VCO of
5% hold-in range and an input sensitivity of
about 300 mV.
DS007981-26
Figure 21
uses the four-quadrant
Figure 18
to produce a
FIGURE 20. Multiplexer
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DS007981-27
Page 17
Additional Applications (Continued)
FIGURE 21. Phase Lock Loop
The Schmitt Trigger of
current into R to set the hysteresis of the comparator; thus
V
=2xRxIB. VaryingIBwill produce a Schmitt Trigger with
H
variable hysteresis.
Figure 22
uses the amplifier output
LM13700
DS007981-28
FIGURE 22. Schmitt Trigger
DS007981-29
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Page 18
Additional Applications (Continued)
Figure 23
LM13700
verter. Whenever A1 is toggled by a positive-going input, an
amount of charge equal to (V
R
t
rent of V
time required to charge C
where V
high output voltage swing of the LM13700. D1 is added to
provide a discharge path for C
shows a Tachometeror Frequency-to-Voltage con-
H–VL)Ct
is sourced into Cfand
. This once per cycle charge is then balanced by the cur-
. The maximum FINis limited by the amount of
O/Rt
and VHrepresent the maximum low and maximum
L
from VLto VHwith a current of IB,
t
when A1 switches low.
t
The Peak Detector of
ever V
IN
storage capacitor C to hold V
output of A2 low through D1 serves to turn off A1 so that V
remains constant.
FIGURE 23. Tachometer
Figure 24
usesA2 to turn on A1 when-
becomes more positive than VO. A1 then charges
equal to VINPK. Pulling the
O
DS007981-30
O
FIGURE 24. Peak Detector and Hold Circuit
The Ramp-and-Hold of
Figure 26
sources IBinto capacitor C
whenever the input to A1 is brought high, giving a ramp-rate
of about 1V/ms for the component values shown.
The true-RMS converter of
Figure 27
is essentially an automatic gain control amplifier which adjusts its gain such that
the AC power at the output of amplifier A1 is constant. The
output power of amplifier A1 is monitored by squaring amplifier A2 and the average compared to a reference voltage
with amplifier A3. The output of A3 provides bias current to
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DS007981-31
the diodes of A1 to attenuate the input signal. Because the
output power of A1 is held constant, the RMS value is constant and the attenuation is directly proportional to the RMS
value of the input voltage. The attenuation is also proportional to the diode bias current. Amplifier A4 adjusts the ratio
of currents through the diodes to be equal and therefore the
voltage at the output of A4 is proportional to the RMS value
of the input voltage. The calibration potentiometer is set such
that V
reads directly in RMS volts.
O
Page 19
Additional Applications (Continued)
FIGURE 25. Sample-Hold Circuit
LM13700
DS007981-32
FIGURE 26. Ramp and Hold
DS007981-33
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Page 20
Additional Applications (Continued)
LM13700
FIGURE 27. True RMS Converter
The circuit of
Figure 28
is a voltage reference of variable
Temperature Coefficient. The 100 kΩ potentiometer adjusts
the output voltage which has a positive TC above 1.2V, zero
TC at about 1.2V, and negative TC below 1.2V. This is accomplished by balancing the TC of the A2 transfer function
against the complementary TC of D1.
The wide dynamic range of the LM13700 allows easy control
of the output pulse width in the Pulse Width Modulator of
ure 29
.
For generating I
rent, the system of
over a range of 4 to 6 decades of cur-
ABC
Figure 30
provides a logarithmic current
Fig-
out for a linear voltage in.
Since the closed-loop configuration ensures that the input to
A2 is held equal to 0V, the output current of A1 is equal to
I
=−VC/RC.
3
The differential voltage between Q1 and Q2 is attenuated by
the R1,R2 network so that A1 may be assumed to be operating within its linear range. From
Equation (5)
, the input volt-
age to A1 is:
DS007981-34
The voltage on the base of Q1 is then
The ratio of the Q1 and Q2 collector currents is defined by:
Combining and solving for I
This logarithmic current can be used to bias the circuit of
ure 4
to provide temperature independent stereo attenuation
ABC
yields:
Fig-
characteristic.
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Page 21
Additional Applications (Continued)
LM13700
FIGURE 28. Delta VBE Reference
DS007981-35
FIGURE 29. Pulse Width Modulator
DS007981-36
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Page 22
Additional Applications (Continued)
LM13700
DS007981-37
FIGURE 30. Logarithmic Current Source
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Page 23
Physical Dimensions inches (millimeters) unless otherwise noted
S.O. Package (M)
Order Number LM13700M or LM13700MX
NS Package Number M16A
LM13700
Molded Dual-In-Line Package (N)
Order Number LM13700N
NS Package Number N16A
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Page 24
Notes
LIFE SUPPORT POLICY
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 AND GENERAL
COUNSEL 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
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.
labeling, can be reasonably expected to result in a
significant injury to the user.
National Semiconductor
Corporation
Americas
LM13700 Dual Operational Transconductance Amplifiers with Linearizing Diodes and Buffers
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.
Tel: 1-800-272-9959
Fax: 1-800-737-7018
Email: support@nsc.com
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Europe
Fax: +49 (0) 180-530 85 86
Email: europe.support@nsc.com
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Response Group
Tel: 65-2544466
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Email: ap.support@nsc.com
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Tel: 81-3-5639-7560
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