TL054MFKB View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
TL054MFKB Datasheet PDF : 67 Pages
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TL05x, TL05xA
ENHANCED-JFET LOW-OFFSET
OPERATIONAL AMPLIFIERS
SLOS178A – FEBRUARY 1997 - REVISED FEBRUARY 2003
APPLICATION INFORMATION
high input impedance log amplifier
The low input offset voltage and high input impedance of the TL05xA creates a precision log amplifier (see
Figure 87). IC1 is a 2.5-V, low-current precision, shunt regulator. Transistors Q1 and Q2 must be a closely
matched npn pair. For best performance over temperature, R4 should be a metal-film resistor with a low
temperature coefficient.
In this circuit, U1A serves as a high-impedance unity-gain buffer. Amplifier U1B converts the input voltage to
a current through R1 and Q1. Amplifier U1C, IC1, and R4 form a 1-µA temperature-stable current source that
sets the base-emitter voltage of Q2. U1D amplifies the difference between the base-emitter voltage of Q1 and
Q2 (see Figure 88). The output voltage is given by the following equation:
+ ƪ ) ƫ ȧȱȲ ǒ Ǔȳȴȧ + + VO
–1
R6 kT
R5 q
In
R1
VI
where k 1.38 10–23, q
1 10–6 and T is Kelvin temperature
1.602
10–19,
Q1
Q2
R4
+
R1
VI
_U1A
10 kΩ
15 V
+
U_ 1B
–15V
2N2484
R2
10 kΩ
R3
270 kΩ
2.5 MΩ
+
_U1C
C1
150 pF
IC1
R5
10 kΩ
+
_U1D
R6
10 kΩ
VO
(see equation above)
NOTE A: U1A through U1D = TL05xA. IC1 = LM385, LT1004, or LT1009 voltage reference
Figure 87. Log Amplifier
–0.1
–0.15
–0.2
–0.25
–0.3
–0.35
ÁÁÁÁ–0.4
ÁÁ 0
1
2
3
4
5
6
7
8
9
10
f – Frequency – Hz
Figure 88. Output Voltage vs Input Voltage for Log Amplifier
44
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