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TL032CD  ENHANCEDJFET LOWPOWER LOWOFFSET OPERATIONAL AMPLIFIERS  Texas Instruments 
TL032CD Datasheet PDF : 68 Pages

TL03x, TL03xA
ENHANCEDJFET LOWPOWER LOWOFFSET
OPERATIONAL AMPLIFIERS
SLOS180C – FEBRUARY 1997 – REVISED DECEMBER 2001
APPLICATION INFORMATION
transimpedance amplifier
The lowpower precision TL03x allows accurate measurement of low currents. The high input impedance and
low offset voltage of the TL03xA greatly simplify the design of a transimpedance amplifier. At room temperature,
this design achieves 10bit accuracy with an error of less than 1/2 LSB.
+ ǒ ) Ǔ Assuming that R2 is much less than R1 and ignoring error terms, the output voltage can be expressed as:
VO
– IIN
RF
R1 R2
R2
Using the resistor values shown in the schematic for a 1nA input current, the output voltage equals –0.1 V. If
the VO limit for the TL03xA is measured at ±12 V, the maximum input current for these resistor values is ±120 nA.
Similarly, one LSB on a 10bit scale corresponds to 12 mV of output voltage, or 120 pA of input current.
+ ƪ ) ǒ ) Ǔƫǒ ) Ǔ The following equation shows the effect of input offset voltage and input bias current on the output voltage:
VO
– VIO
RF IIO
IIB
R1 R2
R2
If the application requires input protection for the transimpedance amplifier, do not use standard PN diodes.
Instead, use lowleakage Siliconix SN4117 JFETs (or equivalent) connected as diodes across the TL03xA
inputs (see Figure 65).
As with all precision applications, special care must be taken to eliminate external sources of leakage and
interference. Other precautions include using highquality insulation, cleaning insulating surfaces to remove
fluxes and other residue, and enclosing the application within a protective box.
RF
10 MΩ
15 V
Input Current
+ TL03xA
VO
–
–15 V R1 90 kΩ
SN4117
R2 10 kΩ
Figure 65. Transimpedance Amplifier
44
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265

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