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NE5517N View Datasheet(PDF) - ON Semiconductor

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NE5517N Datasheet PDF : 14 Pages
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NE5517, NE5517A, AU5517
Linearizing Diodes
For VIN greater than a few millivolts, Equation 3 becomes
invalid and the transconductance increases non-linearly.
Figure 22 shows how the internal diodes can linearize the
transfer function of the operational amplifier. Assume D2
and D3 are biased with current sources and the input signal
current is IS. Since I4 + I5 = IB and I5 − I4 = I0,
that is: I4 = (IB − I0), I5 = (IB + I0)
Impedance Buffer
The upper limit of transconductance is defined by the
maximum value of IB (2.0 mA). The lowest value of IB for
which the amplifier will function therefore determines the
overall dynamic range. At low values of IB, a buffer with
very low input bias current is desired. A Darlington
amplifier with constant-current source (Q14, Q15, Q16, D7,
D8, and R1) suits the need.
+VS
APPLICATIONS
ID
ID
ID
2 * IS 2 ) IS
ǒ ǓIB
I0 + 2 IS ID
I0 + I5 * I4
D3
1/2ID
IS IS
1/2ID
I4
D2
Q4
I5
I5
IB
−VS
Figure 22. Linearizing Diode
For the diodes and the input transistors that have identical
geometries and are subject to similar voltages and
temperatures, the following equation is true:
T
q
In
ID
2
)
IS
ID
2
*
IS
+
KT
q
In
1ń2(IB ) IO)
1ń2(IB * IO)
(eq. 6)
IO +
IS
2IB
ID
for
|IS| t
ID
2
The only limitation is that the signal current should not
exceed ID.
Voltage-Controlled Amplifier
In Figure 23, the voltage divider R2, R3 divides the
input-voltage into small values (mV range) so the amplifier
operates in a linear manner.
It is:
IOUT
+
*VIN
@
R2
R3
)
R3
@
gM;
VOUT + IOUT @ RL;
A
+
VOUT
VIN
+
R2
R3
)
R3
@
gM
@
RL
(3) gM = 19.2 IABC
(gM in mmhos for IABC in mA)
Since gM is directly proportional to IABC, the amplification
is controlled by the voltage VC in a simple way.
When VC is taken relative to −VCC the following formula
is valid:
IABC
+
(VC
* 1.2V)
R1
The 1.2 V is the voltage across two base-emitter baths in
the current mirrors. This circuit is the base for many
applications of the AU5517/NE5517.
VC
+VCC
R4 = R2/ /R3 3 +
R1
11 1
IABC
NE5517
5
7
VIN
R2
6
4
IOUT
RL
R3
TYPICAL VALUES: R1 = 47kW
R2 = 10kW
R3 = 200W
R4 = 200W
RL = 100kW
RS = 47kW
Figure 23.
INT
+VCC
8
VOUT
RS
INT
−VCC
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