NSC LM13700AN Datasheet
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
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
www.national.com 2
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
www.national.com3
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
www.national.com 4
DS007981-48
DS007981-49
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)
www.national.com5
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
www.national.com 6
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
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-
www.national.com7
Stereo Volume Control (Continued)
LM13700
DS007981-11
FIGURE 4. Stereo Volume Control
FIGURE 5. Amplitude Modulator
www.national.com 8
DS007981-12
Loading...