TLC27L1 Datasheet, PDF (20/32 Pages) Texas Instruments – LinCMOSE LOW-POWER OPERATIONAL AMPLIFIERS

TLC27L1, TLC27L1A, TLC27L1B
LinCMOS™ LOW-POWER
OPERATIONAL AMPLIFIERS
SLOS154 – DECEMBER 1995
PARAMETER MEASUREMENT INFORMATION
single-supply versus split-supply test circuits (continued)
2 kΩ
2 kΩ
20 Ω
VDD
VDD ₊
1/2 VDD
20 Ω
VO
VO
20 Ω
20 Ω
(a) SINGLE SUPPLY
VDD _–
(b) SPLIT SUPPLY
Figure 34. Noise-Test Circuit
10 kΩ
10 kΩ
VI
1/2 VDD
100 Ω
VDD
VO
CL
100 Ω
VI
VDD ₊
VO
CL
(a) SINGLE SUPPLY
VDD _–
(b) SPLIT SUPPLY
Figure 35. Gain-of-100 Inverting Amplifier
input bias current
Due to the high input impedance of the TLC27L1 operational amplifiers, attempts to measure the input bias
current can result in erroneous readings. The bias current at normal room ambient temperature is typically less
than 1 pA, a value that is easily exceeded by leakages on the test socket. Two suggestions are offered to avoid
erroneous measurements:
1. Isolate the device from other potential leakage sources. Use a grounded shield around and between the
device inputs (see Figure 36). Leakages that would otherwise flow to the inputs are shunted away.
2. Compensate for the leakage of the test socket by actually performing an input bias-current test (using a
picoammeter) with no device in the test socket. The actual input bias current can then be calculated by
subtracting the open-socket leakage readings from the readings obtained with a device in the test socket.
One word of caution: many automatic testers as well as some bench-top operational amplifier testers use the
servo-loop technique with a resistor in series with the device input to measure the input bias current (the voltage
drop across the series resistor is measured and the bias current is calculated). This method requires that a
device be inserted into the test socket to obtain a correct reading; therefore, an open-socket reading is not
feasible using this method.
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