TLC27L1 Datasheet, PDF (24/32 Pages) Texas Instruments – LinCMOSE LOW-POWER OPERATIONAL AMPLIFIERS

TLC27L1, TLC27L1A, TLC27L1B
LinCMOS™ LOW-POWER
OPERATIONAL AMPLIFIERS
SLOS154 – DECEMBER 1995
APPLICATION INFORMATION
input characteristics (continued)
The use of the polysilicon-gate process and the careful input circuit design gives the TLC27L1 very good input
offset-voltage drift characteristics relative to conventional metal-gate processes. Offset-voltage drift in CMOS
devices is highly influenced by threshold voltage shifts caused by polarization of the phosphorus dopant
implanted in the oxide. Placing the phosphorus dopant in a conductor (such as a polysilicon gate) alleviates the
polarization problem, thus reducing threshold voltage shifts by more than an order of magnitude. The
offset-voltage drift with time has been calculated to be typically 0.1 µV/month, including the first month of
operation.
Because of the extremely high input impedance and resulting low bias-current requirements, the TLC27L1 is
well suited for low-level signal processing; however, leakage currents on printed circuit boards and sockets can
easily exceed bias-current requirements and cause a degradation in device performance. It is good practice
to include guard rings around inputs (similar to those of Figure 36 in the Parameter Measurement Information
section). These guards should be driven from a low-impedance source at the same voltage level as the
common-mode input (see Figure 41).
noise performance
The noise specifications in operational amplifier circuits are greatly dependent on the current in the first-stage
differential amplifier. The low-input bias-current requirements of the TLC27L1 results in a very-low noise current,
which is insignificant in most applications. This feature makes the devices especially favorable over bipolar
devices when using values of circuit impedance greater than 50 kΩ, since bipolar devices exhibit greater noise
currents.
VI ^{ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ VO VI}
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ _{VO VI}
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ _VO
(a) NONINVERTING AMPLIFIER
(b) INVERTING AMPLIFIER
Figure 41. Guard-Ring Schemes
(c) UNITY-GAIN AMPLIFIER
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